50-70 sistema de negociação de alta probabilidade

Sistema inteligente de negociação de ações, confirmando o ponto de viragem e raciocínio probabilístico.
A engenharia financeira, como a decisão de negociação, é uma área de pesquisa emergente e também possui grandes potenciais comerciais. Uma compra / venda de ações bem sucedida geralmente ocorre perto do ponto de virada da tendência de preço. A análise técnica tradicional baseia-se em algumas estatísticas (por exemplo, indicadores técnicos) para prever o ponto de viragem da tendência. No entanto, esses indicadores não podem garantir a precisão da previsão no domínio caótico. Neste artigo, propomos um sistema inteligente de negociação financeira através de uma nova abordagem: aprender a estratégia de negociação por modelo probabilístico a partir da representação de alto nível de séries temporais - pontos de virada e indicadores técnicos. As principais contribuições deste artigo são duas. Primeiro, utilizamos a representação de alto nível (ponto de viragem e indicadores técnicos). A representação de alto nível tem várias vantagens, como insensibilidade ao ruído e intuitivo ao ser humano. No entanto, raramente é usado em pesquisas anteriores. Indicador técnico é o conhecimento de investidores profissionais, que geralmente podem caracterizar o mercado. Segundo, combinando a representação de alto nível com o modelo probabilístico, a aleatoriedade e a incerteza do sistema caótico são ainda mais reduzidas. Desta forma, alcançamos grandes resultados (experimentos abrangentes sobre os componentes S & amp; P500) em um domínio caótico em que a previsão é considerada impossível no passado.
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50-70 sistema de negociação de alta probabilidade
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Aquisições parciais, a hipótese de probabilidade de aquisição e os retornos anormais para metas parciais.
A aquisição de uma participação parcial em uma empresa alvo tem sido positivamente vinculada à probabilidade de que a meta estará envolvida em uma aquisição integral subsequente envolvendo o licitante original ou um licitante de terceiros. Os estudos existentes fornecem apenas evidências sugestivas dessa ligação comparando os retornos anormais aos alvos parciais que são finalmente adquiridos àqueles que não são. Usando uma amostra de aquisições parciais, identificamos características que impactam a probabilidade de uma aquisição completa e fornecem uma ligação tangível entre os ganhos de meta parciais e a probabilidade ex ante de aquisição. Alvos parciais experimentam efeitos de anúncio positivos, e os ganhos são maiores para alvos adquiridos posteriormente. Licitações parciais iniciadas por licitantes corporativos têm maior probabilidade de resultar em uma aquisição completa, e o tamanho da participação adquirida e o nível de propriedade institucional estão positivamente ligados à probabilidade de aquisição. Além disso, os ganhos de meta parciais estão positivamente ligados à probabilidade ex ante de aquisição, mesmo após o controle de qualquer monitoramento e disciplina que o licitante parcial deva impor. As descobertas são robustas em vários horizontes temporais e especificações de modelos.
Classificação JEL.
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Resumo das Cotações.
Principais dados de ganhos.
* BMO = Antes do Mercado Aberto * AMC = Após o Mercado Fechar.
Zacks Earnings ESP (Previsão de Surpresa Esperada) procura encontrar surpresas de lucros, concentrando-se nas revisões de analistas mais recentes. Isso é feito porque, em geral, se um analista reavaliar sua estimativa de ganhos logo antes de uma liberação de resultados, isso significa que eles têm novas informações que poderiam ser mais precisas do que o que os analistas pensavam sobre uma empresa há dois ou três meses.
O ponto crucial dessa abordagem é comparar a Estimativa mais precisa para a estimativa de consenso de Zacks, embora o Rank Zacks também seja uma característica importante da métrica ESP. Combinar esses dois pode ajudar os investidores a encontrar ações que estão prontas para superar o consenso em seu próximo relatório, e espero que eleve mais alto no preço também.
Na verdade, ao combinar um Zacks Rank # 3 ou melhor e um Earnings ESP positivo, os estoques produziram uma surpresa positiva de 70% do tempo. E o melhor de tudo, ao usar esses parâmetros, os investidores viram em média 28,3% de retornos anuais, de acordo com nosso backtest de 10 anos.
Relatório de pesquisa para AL.
Pesquisa Premium para AL.
Um valor | F Crescimento | F Momentum | D VGM.
Este é o nosso sistema de classificação de curto prazo que serve como um indicador de oportunidade para os estoques nos próximos 1 a 3 meses. Quão bom é isso? Veja as classificações e o desempenho relacionado abaixo.
Zacks Rank Education - Saiba mais sobre o Rank Zacks.
Zacks Rank Home - Todos os recursos Zacks Rank em um só lugar.
Zacks Premium - A única maneira de obter acesso ao Zacks Rank.
As pontuações de estilo são um conjunto complementar de indicadores para usar junto com a classificação de Zacks. Ele permite que o usuário se concentre melhor nas ações que melhor atendem ao seu estilo de negociação pessoal.
As pontuações são baseadas nos estilos de negociação de Valor, Crescimento e Momento. Há também uma pontuação VGM ('V' para Value, 'G' para Growth e 'M' para Momentum), que combina a média ponderada das pontuações de estilo individuais em uma pontuação.
Dentro de cada pontuação, as ações são classificadas em cinco grupos: A, B, C, D e F. Como você deve se lembrar de seus dias de escola, um A é melhor que um B; um B é melhor do que um C; um C é melhor do que um D; e um D é melhor que um F.
Como investidor, você quer comprar ações com a maior probabilidade de sucesso. Isso significa que você quer comprar ações com um Zacks Rank # 1 ou # 2, Strong Buy ou Buy, que também tem uma pontuação de um A ou B no seu estilo de negociação pessoal.
Zacks Style Scores Education - Saiba mais sobre as classificações de estilo Zacks.
O Rank da Indústria de Zacks atribui uma classificação a cada uma das 265 X (Expandidas) Indústrias com base na classificação média de Zacks.
Uma indústria com uma percentagem maior de Zacks Rank # 1 e apostas e # 2 terá uma classificação média melhor de Zacks do que uma com uma porcentagem maior de Zacks Rank # 4 & apos; s e # 5 & apos; s.
A indústria com a melhor classificação média de Zacks seria considerada a principal indústria (1 em 265), o que colocaria no topo 1% das indústrias classificadas de Zacks. A indústria com a pior classificação média de Zacks (265 de 265) colocaria no fundo 1%.
Zacks Rank Education - Saiba mais sobre o Rank Zacks.
Zacks Industry Rank Educação - Saiba mais sobre o Zacks Industry Rank.
O Zacks Sector Rank atribui uma classificação a cada um dos 16 setores com base na classificação média de Zacks.
Um setor com uma porcentagem maior de Zacks Rank # 1 & apos; s e # 2 terá um Rank Zacks médio melhor do que um com uma porcentagem maior de Zacks Rank # 4 & apos; s e # 5 & apos; s.
Educação de Rank de Setor de Zacks - Saiba mais sobre a Classificação do Setor de Zacks.
O setor com a melhor classificação média de Zacks seria considerado o setor superior (1 em 16), o que o colocaria no topo 1% dos setores classificados de Zacks. O setor com a pior classificação média de Zacks (16 de 16) colocaria na parte inferior 1%.
Zacks Rank Education - Saiba mais sobre o Rank Zacks.
Educação de Rank de Setor de Zacks - Saiba mais sobre a Classificação do Setor de Zacks.
Os relatórios da Zacks Equity Research, ou ZER para breve, são nossos relatórios de pesquisa internos, produzidos independentemente.
Os sempre populares relatórios de instantâneo de uma página são gerados para praticamente todos os estoques de Zacks Classificados. Está cheio de todas as estatísticas-chave da empresa e informações importantes para a tomada de decisões. Incluindo o Zacks Rank, o Zacks Industry Rank, o Style Scores, o Price, Consensus & Surprise, análise de estimativa gráfica e como as ações se acumulam aos seus pares.
O relatório detalhado de análise de várias páginas faz um mergulho ainda mais profundo nas estatísticas vitais da empresa. Além de toda a análise proprietária no Snapshot, o relatório também exibe visualmente os quatro componentes do Rank do Zacks (Acordo, Magnitude, Upside e Surprise); fornece uma visão abrangente dos drivers de negócios da empresa, completa com gráficos de ganhos e vendas; um recapitulação de seu último relatório de ganhos; e uma lista com balas para comprar ou vender o estoque. Também inclui uma tabela de comparação da indústria para ver como seu estoque se compara ao seu setor expandido e ao S & amp; P 500.
Investigar ações nunca foi tão fácil ou perspicaz quanto com os relatórios do ZER Analyst e Snapshot.
Zacks Earnings ESP (Previsão de Surpresa Esperada) procura encontrar empresas que tenham visto recentemente uma atividade positiva de revisão de estimativas positivas. A idéia é que a informação mais recente é, em geral, mais precisa e pode ser um melhor preditor do futuro, o que pode dar aos investidores uma vantagem na temporada de lucros.
A técnica provou ser muito útil para encontrar surpresas positivas. Na verdade, ao combinar um Zacks Rank # 3 ou melhor e um Earnings ESP positivo, os estoques produziram uma surpresa positiva de 70% do tempo, enquanto também viram retornos anuais de 28,3% em média, de acordo com nosso backtest de 10 anos.
Este é o nosso sistema de classificação de curto prazo que serve como um indicador de oportunidade para os estoques nos próximos 1 a 3 meses. Quão bom é isso? Veja as classificações e o desempenho relacionado abaixo.
Zacks Rank Education - Saiba mais sobre o Rank Zacks.
Zacks Rank Home - Todos os recursos Zacks Rank em um só lugar.
Zacks Premium - A única maneira de acessar completamente o Rank Zacks.
O Rank da Indústria de Zacks atribui uma classificação a cada uma das 265 X (Expandidas) Indústrias com base na classificação média de Zacks.
Uma indústria com uma percentagem maior de Zacks Rank # 1 e apostas e # 2 terá uma classificação média melhor de Zacks do que uma com uma porcentagem maior de Zacks Rank # 4 & apos; s e # 5 & apos; s.
A indústria com a melhor classificação média de Zacks seria considerada a principal indústria (1 em 265), o que colocaria no topo 1% das indústrias classificadas de Zacks. A indústria com a pior classificação média de Zacks (265 de 265) colocaria no fundo 1%.
Zacks Rank Education - Saiba mais sobre o Rank Zacks.
Zacks Industry Rank Educação - Saiba mais sobre o Zacks Industry Rank.
O Zacks Sector Rank atribui uma classificação a cada um dos 16 setores com base na classificação média de Zacks.
Um setor com uma porcentagem maior de Zacks Rank # 1 & apos; s e # 2 terá um Rank Zacks médio melhor do que um com uma porcentagem maior de Zacks Rank # 4 & apos; s e # 5 & apos; s.
Educação de Rank de Setor de Zacks - Saiba mais sobre a Classificação do Setor de Zacks.
O setor com a melhor classificação média de Zacks seria considerado o setor superior (1 em 16), o que o colocaria no topo 1% dos setores classificados de Zacks. O setor com a pior classificação média de Zacks (16 de 16) colocaria na parte inferior 1%.
Zacks Rank Education - Saiba mais sobre o Rank Zacks.
Educação de Rank de Setor de Zacks - Saiba mais sobre a Classificação do Setor de Zacks.
As pontuações de estilo são um conjunto complementar de indicadores para usar junto com a classificação de Zacks. Ele permite que o usuário se concentre melhor nas ações que melhor atendem ao seu estilo de negociação pessoal.
Os três resultados são baseados nos estilos de negociação de Crescimento, Valor e Momentum.
Dentro de cada pontuação, as ações são classificadas em cinco grupos: A, B, C, D e F. Como você pode se lembrar dos dias escolares, um A é melhor do que um B; um B é melhor do que um C; um C é melhor do que um D; e um D é melhor que um F.
Como investidor, você quer comprar ações com a maior probabilidade de sucesso. Isso significa que você quer comprar ações com um Zacks Rank # 1 ou # 2, Strong Buy ou Buy, que também tem uma pontuação de um A ou um B.
Zacks Style Scores Education - Saiba mais sobre as classificações de estilo Zacks.
As pontuações de estilo são um conjunto complementar de indicadores para usar junto com a classificação de Zacks. Ele permite que o usuário se concentre melhor nas ações que melhor atendem ao seu estilo de negociação pessoal.
As pontuações são baseadas nos estilos de negociação de Valor, Crescimento e Momento. Há também uma pontuação VGM ('V' para Value, 'G' para Growth e 'M' para Momentum), que combina a média ponderada das pontuações de estilo individuais em uma pontuação.
Dentro de cada pontuação, as ações são classificadas em cinco grupos: A, B, C, D e F. Como você deve se lembrar de seus dias de escola, um A é melhor que um B; um B é melhor do que um C; um C é melhor do que um D; e um D é melhor que um F.
Como investidor, você quer comprar ações com a maior probabilidade de sucesso. Isso significa que você quer comprar ações com um Zacks Rank # 1 ou # 2, Strong Buy ou Buy, que também tem uma pontuação de um A ou B no seu estilo de negociação pessoal.
Zacks Style Scores Education - Saiba mais sobre as classificações de estilo Zacks.
Os relatórios da Zacks Equity Research, ou ZER para breve, são nossos relatórios de pesquisa internos, produzidos independentemente.
Os sempre populares relatórios de instantâneo de uma página são gerados para praticamente todos os estoques de Zacks Classificados. Está cheio de todas as estatísticas-chave da empresa e informações importantes para a tomada de decisões. Incluindo o Zacks Rank, o Zacks Industry Rank, o Style Scores, o Price, Consensus & Surprise, análise de estimativa gráfica e como as ações se acumulam aos seus pares.
O relatório detalhado de análise de várias páginas faz um mergulho ainda mais profundo nas estatísticas vitais da empresa. Além de toda a análise proprietária no Snapshot, o relatório também exibe visualmente os quatro componentes do Rank do Zacks (Acordo, Magnitude, Upside e Surprise); fornece uma visão abrangente dos drivers de negócios da empresa, completa com gráficos de ganhos e vendas; um recapitulação de seu último relatório de ganhos; e uma lista com balas para comprar ou vender o estoque. Também inclui uma tabela de comparação da indústria para ver como seu estoque se compara ao seu setor expandido e ao S & amp; P 500.
Investigar ações nunca foi tão fácil ou perspicaz quanto com os relatórios do ZER Analyst e Snapshot.
(= Mudança nos últimos 30 dias)
Pesquisa Premium: Análise da Indústria.
Zacks News para o AL.
Esqueça a Miss do Walmart, compre esses estoques que provavelmente renderão ganhos.
É uma batida na loja para Allegiant (ALGT) no 4º trimestre?
AL: O que os especialistas Zacks estão dizendo agora?
Zacks Private Portfolio Services.
Novas ações da Strong Buy para 19 de janeiro.
Novas ações de compra forte para 17 de janeiro.
A Air Lease Corporation (AL) é uma grande empresa para investidores em valor?
Resumo da empresa.
A Air Lease Corporation é uma empresa de leasing de aeronaves que se dedica principalmente à compra de aeronaves comerciais e leasing para companhias aéreas em todo o mundo. A Companhia presta serviços de leasing na Ásia, no Pacífico, na América Latina, no Oriente Médio e no Leste Europeu. A Air Lease Corporation está sediada em Los Angeles, Califórnia.
Copyright 2018 Zacks Investment Research.
No centro de tudo o que fazemos é um forte compromisso com pesquisas independentes e compartilhando suas descobertas lucrativas com os investidores. Essa dedicação para dar aos investidores uma vantagem comercial levou à criação do nosso comprovado sistema de classificação de estoque Zacks Rank. Desde 1988, mais que dobrou o S & P 500, com um ganho médio de + 25% ao ano. Estes retornos cobrem um período de 1988-2017. Os retornos do sistema de classificação de estoque do Rank de Zacks Rank são calculados mensalmente com base no início do mês e no final do mês, os preços das ações da Zacks Rank mais os dividendos recebidos durante esse mês em particular. Um retorno médio simples e igualmente ponderado de todas as ações do Rank Zacks é calculado para determinar o retorno mensal. Os retornos mensais são então combinados para chegar ao retorno anual. Apenas os estoques de Zacks Rank incluídos nas carteiras hipotéticas de Zacks no início de cada mês estão incluídos nos cálculos de devolução. As ações da Zack Ranks podem, e muitas vezes mudam ao longo do mês. Certas ações do Zacks Rank para as quais nenhum preço de fim de mês estava disponível, as informações de preços não foram coletadas, ou por outros motivos foram excluídos desses cálculos de retorno.
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Os dados da NYSE e AMEX estão com pelo menos 20 minutos de atraso. Os dados do NASDAQ são pelo menos 15 minutos atrasados.

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POPENOE, P. B. (1973): A tamareira. Henry Field, ed., Projetos de Pesquisa de Campo, Coco, Miami, Flórida. 247 pp.
POULAIN, C; A. RHISS, & amp; G. BEAUCHÈSNE. (1979): Multiplicação vegetativa en cultura in vitro de palmier dattier (P. dactylifera L.). C. R. Acad. Agric. 11: 1151-1154.
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REAM, C. L. & amp; J. R. FURR. (1970): Conjunto de datas de frutas afetadas pela viabilidade do pólen e poeira ou água em estigmas. Date Growers & # 8217; Inst Report 47:11.
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REUVENI, O. (1979): Embriogênese e crescimento de plântulas de tamareiras (P. dactylifera L.) derivadas de tecidos de calo. Plant Physio. 63: 138 (Resumo).
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VAN ZYL, H. J. (1983): Date Cultivation in South Africa. Information Bulletin No. 504; Compiled by the Fruit and Fruit Technology Research Institute, Department of Agriculture, Stellenbosch, RSA. 26pp.
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YOST, L. (1968): Correction of Barhee bending by bunch handling practices. Ann. Date Growers’ Instit. 45:2.
ZAID, A. (1981): Rapid propagation of the date palm through tissue culture. Master of Sciences thesis prepared at the U. S. Date and Citrus Station, Indio, California (U. S.A.) 178 pp.
ZAID, A. (1984): In vitro Browning of Tissues and Media with special emphasis to date palm cultures. Date Palm Journal 3(I): 269-275.
ZAID, A. (1985): Multiplication Rapide du Palmier dattier par culture de tissus, Seminaire Agronomie Saharienne. Marrakech, Maroc, du 6 au 8 Mai.
ZAID, A. (1986a): Review of Date Palm Tissue Culture. Second Symposium of Date Palm held in Saudi Arabia. 3-6 March: 67-75.
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ZAID, A. (1987c): Refl exions sur la conformité génétique des Vitro-Plants: Cas du Palmier Dattier. Bulletin du Réseau Maghrebin de Recherche sur la phoeniciculture et la production du palmier dattier. Vol. 1. No. 4.: 12-28.
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ZAID, A. (1999): African Palm Weevil Rhynchophorus phoenicis F. Attack on Date Palm in the Republic of South Africa and Zimbabwe. Middle East Red Palm Weevil Workshop, 26-29 January, 1999; Cairo-Egypt.
ZAID, A., & B. H. TISSERAT. (1983a): In vitro shoot tip differentiation in Phoenix dactylifera L. Date Palm Journal 2 (2): 163-182.
ZAID, A., & B. H. TISSERAT. (1983b): Morphogenetic responses obtained from a variety of somatic explant tissues. Robô. Mag. Tokyo 96: 67-73.
ZAID, A., & B. H. TISSERAT. (1984): Survey of morphogenetic potential of excised palm embryos in vitro. Crop Research (Hort. Res.) 24: 1-9.
ZAID, A., & M. DJERBI. (1984): An up to date bibliography on tissue culture and vascular wilt diseases of date palm and some other palm species. National Institute of Agronomic Research, Morocco and Regional Project for Palm and Dates Research in the Near East and North Africa, FAO: 51 pp.
ZAID, A., & H. HUGHES. (1989a): In vitro acclimatization of date palm (Phoenix dactylifera L.) plantlets: I. effect of poleythylene glycol on water stress. Third Intern. Conf. of IPBNET. p 43 (Abstract).
ZAID, A., & H. HUGHES. (1989b): II. A quantitative comparaison of epicuticular leaf wax as a function of po-leythylene glycol treatment. Hortscience 24: 122 (Abstract).
ZAID, A., & H. HUGHES. (1989c): In vitro acclimatization of date palm (Phoenix dactylifera L.) plantlets. Compte Rendu du Deuxieme Seminaire Maghrebin sur la multiplication du palmier par les techniques in vitro. PNUD/INRA, pp: 115-124 Marrakech 9-12 Oct. Projet FAD/RAB/88/024.
ZAID, A. & HUGHES. (1995a): In vitro acclimatization of date palm (Phoenix dactylifera L.) plantlets: a quantitative comparison of epicuticular leaf wax as a function of poleythylene glycol treatment. Plant cell reports 15: 111-114.
ZAID, A. & HUGHES. (1995b): A comparison of stomatal function and frequency of in vitro, in vitro polythylene glycol treated, and greenhouse-grown plants of date palm, Phoenix dactylifera L. Trop. Agric. (Trinidad) Vol. 72: N 2: 130-134.
CHAPTER XI: DATE PALM TECHNICAL CALENDAR.
CHAPTER XI: DATE PALM TECHNICAL CALENDAR.
by A. Zaid and P. Klein.
Date Production Support Programme.
This chapter highlights, in detail, the various technical steps needed to ensure the proper establishment of a date palm plantation and its management.
It is worth mentioning that since accurate information was available to the authors from their own experience in Namibia (Southern Hemisphere), it seemed appropriate to base the technical calendar on this region (Figure 89). Nnorthern Hemisphere readers could keep the difference in seasonal times in mind (i. e. fl owering is during July/August in the Southern Hemisphere and February/March in the northern hemisphere; fruit maturation and harvesting are during September/October in the Nnorthern Hemisphere and during February/March in the southern hemisphere).
2. Technical calendar for planting tissue culture plants – follow up during the first year.
& # 8211; Acquire the required amount of microsprayer supports (at a rate of 3 per plant);
& # 8211; Prepare the required amount of protection units made of wire mesh and a shade net (1 per plant). No plant should be planted if no protection unit is available;
& # 8211; Plant wind breaks (at least one year in advance); use Beef wood (Casaurina cunninghummiana or Casuarina glauca) which is characterised by rapid growth, high level of drought, and salt tolerance.
& # 8211; Debusing and levelling;
& # 8211; Layout of lines and rows;
& # 8211; Ripping (± 1.2 m) in both directions on the rows;
& # 8211; Install the irrigation system (secondary and tertiary pipelines only);
& # 8211; Mark the exact position of plants;
& # 8211; Dig holes (0.6 m³), if soil has been cross ripped or 1 m³ if soil was not ripped, and leave open till end of December;
& # 8211; Try to localise old, well matured manure or any other organic material (i. e. maize hay, wheat straw, etc.) that will be used the next month.
& # 8211; Place the irrigation supports (3 per plant) and connect the micro-jets (or drippers). The irrigation schedule is presented in chapter VII;
& # 8211; Mix the well matured manure (3 kg per plant), gypsum (if needed) and NPK fertilisers with the soil removed from the hole;
& # 8211; Put the mixed soil back in the hole;
& # 8211; Start the irrigation cycle 2 to 3 times to allow soil to settle. The decomposition of manure will be initiated. When gypsum is applied, a short term leaching programme should be followed before planting;
& # 8211; Enough time (4 to 6 weeks) should be allowed before planting to avoid the nitrogen negative effect period.
Fertilisation at planting:
The following amounts are to be used per planting hole:
& # 8211; 3 kg of old kraal manure (± 3 spades full);
& # 8211; 2 kg of gypsum (if necessary);
& # 8211; 700 g double superphosphate;
& # 8211; 500 g potassium chloride (or 625 g potassium sulphate); e.
& # 8211; 0.25 kg ammonium sulphate (and another 0.25 kg six weeks later).
& # 8211; Tissue culture plants have been in the nursery for the past 8 to 12 months (depending on variety, their original size at reception from the laboratory, and on the care provided by the farmer). The plants should have been well irrigated (twice per week during winter and 3 times per week during summer; a close monitoring is to be ensured in case the substrate is made of bark), and fertilised according to the following programme: Mix 5 litre of SeaGro (5.5 %, 0.75 %, and 1.6 % of N, P,K, respectively) with 1,000 litres of water and apply at 140 ml per plant. Repeat once every two weeks until transplanting into the fi eld. For practical purposes, the plants could be irrigated with the solution by replacing a normal irrigation schedule;
& # 8211; Select your planting material at the nursery; only plants with at least 4 pinnae leaves are to be transplanted in the fi eld;
& # 8211; Inspect your plants and make sure they are free of diseases and pests. In the future plantation, use the Integrated Pest Management Approach (manual or mechanical weeding, light traps, etc.);
& # 8211; Review and ensure the identifi cation of each plant; where different varieties are being planted, use different colour labelling for each variety;
& # 8211; Each block, row and line is to be labelled. A map of the plantation (variety composition) is to be kept in the offi ce (and/or at home).
February and March are the best months for planting (no wind, no extreme temperatures and the average humidity is about 40 %). Let us suppose that our planting date is March15:
& # 8211; Another irrigation before planting is advised. Irrigate to fi eld water capacity;
& # 8211; Recommended spacing is 10 × 8 (10 m between rows and 8 between palms in a row); 125 palms per one hectare will be the planting density;
& # 8211; Planting should be done early in the morning to avoid transplanting stress, and irrigation should be done immediately after transplanting;
& # 8211; Bags should be cut from the bottom and progressively removed upwards, while the soil is put around the palm’s substrate (to avoid roots damage); all distorted or damaged roots are to be pruned;
& # 8211; The leaf base of the palm should be clearly out of the surface of the soil; planting must be to the depth of the plant’s greatest diameter;
& # 8211; A basin of 1.5 to 1.8 m in diameter and 20 to 30 cm deep is to be built for each palm. Hay or wheat straw is to be used for mulching;
& # 8211; Irrigation cycle depends on the location. However, we recommend (from planting till end of August) 2 hours per cycle and twice a week. From September till March the next year it should be increased to 3 cycles per week and 2 hours each cycle. This irrigation calendar supposes the use of three drippers or microjets per palm at a rate of 32 litre/hour each. The palm will hence receive 96 litres per hour.
& # 8211; At all times, the soil near the newly planted palm should be kept moist through light and frequent irrigation;
& # 8211; The irrigation cycle is to be monitored (use tensiometers if possible), and frequent check-ups are essential to ensure the proper functioning of microjets or drippers;
& # 8211; No leaf pruning is to be practised during the first two years (only leaves that touch the ground could be removed);
& # 8211; The required number of male palms (5 for each ha) are to be planted separately in one block, preferably not in a windy spot and close to the pollen workshop;
& # 8211; Weeding is to be properly implemented;
& # 8211; Next year March: if needed apply 5 kg of gypsum per palm.
& # 8211; April 15 (4 weeks after the planting date): apply 250 g potassium chloride per palm;
& # 8211; April 25: apply if needed 2 kg of gypsum per palm;
& # 8211; Apri 30 (six weeks after the planting date): apply 250 g ammonium sulphate per palm.
& # 8211; May 15: apply the second 250 g potassium chloride per palm;
& # 8211; End of May: assess your survival rate (should be at least 95%).
& # 8211; June 15 (six weeks interval): apply the second 250 g ammonium sulphate per palm;
& # 8211; Once the first year after planting is over, a fertilisation programme is to be applied till the first fl owering year (year 4 or 5 depending on variety, location and provided care). Full detail about the fertilisation programme can be found in Chapter VI.
& # 8211; No offshoots should be left on a palm; they must be removed at an early stage to ensure vigorous growth and early fruit production. Removal of offshoots should be done twice per year (July and December). Make sure that the attachment point between the offshoot and the plant mother is treated with copper oxychlorid (use DEMIL DEX at 500 g in 25 l of PVA paint).
& # 8211; After 4 years, the farmer must implement the following technical calendar.
3. Technical calendar for a date palm plantation older than 4/5 years.
& # 8211; Immediately after harvest, but no later than early May, the cleaning of the palms must be initiated. Old fruitstalks, leaves touching the ground and young offshoots are to be removed since they stress the mother palm, cause its decline and decrease fruit yield. No direct planting of these offshoots should be practised; they must be rooted in the nursery for at least one year;
& # 8211; Removal of spines from about 20 to 25 outside leaves and cleaning of the palms to prepare for pollination;
& # 8211; Leaves with symptoms of diseases need to be removed and burned;
& # 8211; Apply fertilisation on the 1st of April;
& # 8211; Apply potassium chloride fertilisation on the 15th of April;
& # 8211; Apply the ammonium sulphate fertilisation (in April and in May);
& # 8211; If leaching is required, it must be practised before the start of the monthly fertilisation;
& # 8211; The palm’s basin is to be weeded and mulched; e.
& # 8211; Attend to the general maintenance practices such as inspection of all water points (drippers, microjets, etc.), mulching, weeding, repair of basins, etc.
& # 8211; Apply the ammonium sulphate fertilisation;
& # 8211; If male flowers start production, harvest the pollen and dry it;
& # 8211; Monitor a control programme against pests and diseases (avoid the extensive use of chemicals and base your approach on Integrated Pest Management; manual or mechanical weeding, light traps, phenomone traps, removal of diseased leaves, etc.).
& # 8211; Pollination season starts and will continue until the end of August, sometimes until the end of September;
& # 8211; An adult male palm produces between 500 to 1,000 g of pollen (an average of 700 g), which is enough for pollinating 47 female palms; It is clear that 15 to 20 g of pollen is the required amount of pollen to be used per female palm; approximately 2 kg of pollen are needed per hectare.
& # 8211; Germination and humidity tests of stored pollen could be initiated at any convenient located scientific facility; if this is not possible try to use only fresh pollen;
& # 8211; Use mixed pollen (old and fresh); on daily basis, the pollen (just the quantity to be used) is to be mixed with non - perfumed industrial talc (or wheat fl ower) at a rate of 30 to 50 percent depending on varieties.
& # 8211; Medjool only requires a low quantity of pollen (10 % pollen/talc ratio = 1:g);
& # 8211; Only skilled labourers should be used for pollination;
& # 8211; Pollination should only be practised between 10:00 in the morning and 15:00 in the afternoon (not before, nor after). A minimum temperature of 18°C is to be respected;
& # 8211; If it rains within 2 to 3 days after pollination, repeat the pollination;
& # 8211; To pollinate, the female spathes are to be gently opened after they start cracking; cover-sheaths will be removed with no damage to the inside fl owers;
& # 8211; The top 1/3 of the female inflorescence should be removed (1st thinning); do not squeeze the inflorescences while doing this.
& # 8211; Pollination should be applied at least twice with 2 to 3- day intervals (to ensure a good fruit set);
& # 8211; In places where low temperatures are expected during the pollination season, craft paper bags are to be used to cover the pollinated infl orescence. Several days later (8 to 10), the bags must be removed.
& # 8211; A slight leaf pruning could also be practised depending on variety and on the palm’s canopy;
& # 8211; Make sure that the future enlarged inflorescence is not disturbed by surrounding leaves;
& # 8211; Apply the Maxi-Fos fertilisation on the 1st of July;
& # 8211; Apply the ammonium sulphate fertilisation on the 7th of July.
& # 8211; Apply the potassium chloride on the 15th of July.
& # 8211; Two weeks after the last pollination, ensure a passage in each palm and below each infl ores-cence in order to assess the fruit set and to position (if a leaf or two needs to be cut, it must be done at this time); this is to prevent wind/leaf damage on the fruits;
& # 8211; Start marketing contact with potential date traders;
& # 8211; Ensure the availability of packing material;
& # 8211; Initiate logistical planning (storage, transport, etc.);
& # 8211; Apply the ammonium sulphate fertilisation.
Six to eight weeks after the first pollination, start the following:
& # 8211; Bunch removal: Limit the number of fruit bunches per palm to the accepted norms depending on the palm’s age and vigour. Use the formula: an average of 10 leaves per bunch. The bunches kept are the ones with the nice fruit set and well equilibrated around the palm (equally distributed around the crown). One fruit bunch during first year of production, 2 bunches the second year, and so on.
& # 8211; Bunch thinning: Thin from the inside (± 1/3) but do not cut too close to the remaining inside spikelets; leave 5 to 6 cm to avoid drying and fungal attack. Thinning is variety dependent and should be done only after precise evaluation of the fruit set;
& # 8211; The above thinning techniques should always lead to the following fruit distribution:
* Barhee: 45 to 50 spikelets per bunch and 20 to 25 fruits per spikelet. The number of fruits per bunch will vary from 900 to 1,250; with an average of 15 g per fruit, the bunch weight will vary from 13.50 kg to 18.75 kg.
* Medjool: 30 spikelets per bunch and 10 fruits per spikelet. The number of fruits per bunch should be about 300; with an average fruit weight of 20 g (as a semi-dry fruit from 18 to 28 g), the bunch weight will approximately be 6 kg.
& # 8211; Positioning and supporting the bunches: Immediately, after bunch thinning is fi nished at the whole plantation, the operation of positioning and tying is to be practised. Be careful to gently position the bunch in order not to break the fruitstalk (use both hands). Each fruit bunch should be supported (to avoid its future breakage) by the use of two ropes attached to the upper and the lower leaf.
Note that all the above practises (pollination, thinning, etc.) are labour intensive (170 working days/year/hectare), and must only be handled by skilled labour. It is necessary to treat the fl ower/inflorescence with care from pollination till Hababouk stage.
& # 8211; Apply ammonium sulphate fertilisation.
& # 8211; Apply the Maxi-Fos fertilisation on the 1st of October;
& # 8211; Apply the ammonium sulphate fertilisation for October and November;
& # 8211; All bunches are to be covered with net bags (80 %) to protect the fruits from birds, wasps and insects. This period should correspond to the passage of fruits from Kimri to Khalal. Fruits at this stage are starting to turn yellow in colour (case of Barhee variety) and the nets are to be left on the bunches till fruit ripening and harvesting. This protection operation must be completed throughout the whole plantation before the Rutab stage is reached.
& # 8211; Observe irrigation programme;
& # 8211; Apply the Maxi-Fos fertilisation on the 1st of January;
& # 8211; Apply the potassium chloride fertilisation on the 15th of January.
& # 8211; If necessary, all dried and half dried leaves could be pruned during February to avoid the Rutab fruits from damage caused by these leaves during windy situations. It also helps the harvesting operation.
& # 8211; Before harvesting (February preferably), leaves that touch the ground can be removed along with small offshoots.
& # 8211; Harvesting season depends on variety, location and care; it could start early February;
& # 8211; Make sure that fruits are matured and correspond to market needs (maturation test); bunches are tested for export standards;
& # 8211; Good management of harvest, transport to the packing house and packaging process.
& # 8211; Leaf pruning can be summarised as follows:
* Immediately after harvest for the ones touching the ground;
* During the second thinning operation and while positioning the bunch, 1 to 2 leaves per bunch are to be removed if required, to leave free space for the fruit bunch; e.
& # 8211; Weeding around the palm needs to be practised on monthly basis;
& # 8211; Microsprinklers or drippers and palms’s basin need to be maintained on regular basis;
& # 8211; Maintain mulching practices;
& # 8211; Regular fi eld inspections for diseases and pests; e.
& # 8211; Plan in advence the labour requirements;
Table 45 listed in Chapter VI gives details about the fertilisation programme.
Figure 89. Date palm annual technical calendar: Model of Naute (Keetmanshoop), Namibia.
1) Minimum temperature statistics from 1948 till 1985 at Keetmanshoop Airport.
2) August wind direction: N-East and Sept/Oct/Nov: West (severe)
3) 15 February till 15 March is the best planting time(no wind, no extreme temperatures and humidity is relatively high – about 40%
4) Fertilisation and irrigation details are provided in chapter VI and VII, respectively.
CHAPTER X: ESTABLISHMENT OF A MODERN DATE PLANTATION.
CHAPTER X: ESTABLISHMENT OF A MODERN DATE PLANTATION.
by A. Zaid and A. Botes.
Date Production Support Programme.
During the last ten years, reports have indicated the potential and viability for a date production industry. Most of these reports focused on economics and marketing of the date palm at national or regional level. This chapter will concentrate on useful information in both technical and fi nancial aspects for individual farmers. Technical establishment of a date plantation will cover the following components: f easibility study, suitability of the site, selection of varieties to be planted, site preparation, irrigation system and technical practices, while fi nancial establishment will highlight the establishment and operational costs and the cash fl ow statement.
2. Technical establishment of a date plantation.
2.1 Feasibility study.
After being convinced about the marketing potential of dates, and before purchasing land or developing his/her own farm, a potential date grower must seriously look at several factors and consequently conduct a feasibility study before any physical date establishment. The feasibility study should focus on the following:
& # 8211; Survey of the area: with maximum information on its location (latitude, longitude and altitude), vegetation, communications and infrastructure;
& # 8211; Meteorological data: The date grower must contact the nearest weather station to his plantation (within a circle of 30 to 50 km if possible) and request the following data for at least 10 – 15 years:
* Daily values of maximum temperatures (°C);
* Daily values of average temperature (°C);
* Daily values of minimum temperatures (°C);
* Daily values of rain (mm);
* Daily values of evapotranspiration (mm);
* Daily values of sunshine (Hr.);
* Daily values of wind (km);
* Daily values of maximum humidity (%); e.
* Daily values of minimum humidity (%).
& # 8211; Soil analysis: This is a primary factor since it will indicate the success potential of the culture, and will also be used as a guideline for future fertilisation programmes, and irrigation requirements.
& # 8211; Water analysis: The most important factor to look at is the salinity level along with the depth of the underground water table, if any.
& # 8211; Mode of irrigation: Depending on water availability, its quality and also taking into consideration all the above factors, a mode of irrigation system will be selected. Flood irrigation is discouraged for a commercial plantation. In order to ensure high water use-effi ciency the date grower should select either drip or microsprayer systems.
& # 8211; Economical analysis: A local and national market survey is to be implemented to see how promising the market is.
& # 8211; Climatic requirements: The two main climatic requirements for successful cultivation of dates is a long, hot growing season and an absence of heavy rain or high humidity during the ripening period. Frost incidence, is another environmental factor to take into consideration. Details on climatic requirements can be found in Chapter IV.
& # 8211; Water availability: To maximise the probability of a successful date plantation, long term water availability must be ensured. Salinity level must not be too high (5 – 6 % at most) even though adult date palms can survive higher levels (9 – 10 %).
& # 8211; Soil type: Date palms are grown in a wide variety of soils. The optimum soil should have a maximum water-holding capacity and good drainage. Sandy soils require excessive fertilisation and irrigation and permit rapid leaching of mineral nutrients. However, sandy soil that is underlined by more retentive soil of fi ner texture in the first two metres is appreciated. Growth development and fruit quality of dates are reduced under very saline soil conditions.
& # 8211; Labour requirements: Date palm culture is labour intensive during pollination and harvesting/packing periods. Labour requirements for other operations during the year (bunch thinning, pulling down and tying, covering bunches, irrigation, pruning, fertilisa-tion, etc.) are lower.
2.2 Selection of varieties to plant.
Local clones, which are exclusively of seed-origin, must be assessed for their suitability for commercial production. Even though some of these seedlings show signs of measuring up to the best internationally renown varieties, such as Medjool, Bou Fegouss, Barhee, etc, these seedlings must be thoroughly evaluated before large scale multiplication and planting can be initiated. The large scale multiplication and plantation of international renown varieties is essential for reaching the international market and getting high value from the plantation.
2.3 Site preparation.
Once all the above factors and conditions have been assembled, the date grower must concentrate on the preparation of his/her site for the initiation and establishment of the date plantation. To avoid repetition, the reader is invited to refer to Chapter VI.
3. Financial establishment of a date palm plantation.
3.1 Establishment cost.
The introduction of a new enterprise to the farm business can be expensive. However, diversifi cation into date production is seen as part of the bigger existing farming business which will make use of existing infrastructure and mechanisation. Careful planning is thus needed to allocate scarce resources amongst the different farming activities, in a way that the best alternative satisfi es the respective requirements. Detailed calculations are necessary for the farmer to determine the capital needed to implement his/her plan and to forecast its fi nancial result.
It should be kept in mind that costs will vary from one farm to another, depending on the current setup in terms of existing infrastructure and machinery, source of water supply, irrigation system to be used, etc. Costs given are based on a Namibian Date Palm Project (80 ha at Naute/Keetmanshoop), quotations and some estimates of the authors.
In light of possible existing scenarios, the following costs are not included: acquisition of land; source of water supply; mechanisation; and marketing cost. Additional costs needed for date production will be highlighted.
The breakdown of cost items in this paper should be used as a guideline and need to be adapted for each specifi c situation. Table 61 gives an outline of the establishment costs involved per hectare, for a modern plantation of at least 20 ha. The spacing is 10 × 8 m and 125 palms are planted per hectare, of which 5 are males.
Establishment costs per ha for a modern date plantation (US$)
The irrigation system to be installed in a modern plantation should be such that effi ciency is at maximum (at least 85 %) and that volume of water per palm can be controlled. A well planned and effective irrigation system, based on the use of microsprayers or drippers, together with proper management and production practises will result in optimum yields.
The smaller producer establishing only 1 to 5 ha will not install such an expensive irrigation system and it is estimated that the establishment cost might be in the order of US$ 3,200 per ha. This amount includes US$ 2,640 for plant material, US$ 80 for labour, fertiliser and pesticides, and US$ 520 for water supply.
Table 62 gives an outline of additional capital expenses needed to build and equip a modern packing house, for a larger commercial plantation of at least 40 ha. The international food market is very competitive and quality control and hygiene criteria are strict. Thus, to enter the export market successfully and to sustain the supply of quality fruit, the facilities mentioned are essential.
Realising the magnitude of the total costs involved, the immediate question is whether the project will survive. This question will be answered in the sections to follow. It should be kept in mind that date production is a long term project and generates only income from year four or fi ve from establishment. Measures should thus be taken to maintain a cashfl ow during that period.
Various options exist, and the farmer, as a manager, should decide what option best fi ts his skills and business. The following can be successfully implemented as an intercrop: vegetable production; lucerne and citrus. An intercrop will however increase capital investment.
Additional capital expenses (US$): buildings and equipment of a packing house.
One of the advantages of a date plantation is that it creates a special micro climate favourable for other crops. Some plantations in the northern hemisphere, for instance, successfully produce citrus as an intercrop. Because of the high costs of needed facilities, i. e. packing house, cold rooms, labour houses, etc., it seems almost essential to have other crops also utilising these facilities. Other crops sharing these capital expenses have not been considered in the sections to follow.
3.2 Operational cost.
Operational expenses represent those expenditures that occur only if production is undertaken. Capitalisation of the investment cost is dependent upon the production process. Each activity to improve yield and quality costs money and the manager should decide how much, of which activity and at what cost to apply.
A carefully worked out balance of inputs in relation to outputs is needed since maximum production does not necessarily result in maximum profi t.
Tables 63 and 64 represent the activities involved in date production, packaging and marketing with their respective costs over a 10- year period, for large and small commercial date plantations, respectively. Cost indications in Table 63 is per hectare and refl ects the Naute Date project (Namibia), while Table 64 represents activities and respective cost estimates to be encountered by the small date producer (5 ha plantation).
Analysing Table 63, it is clear that the expensive activities are packaging and export marketing. In year 10, full production, pre-harvest costs are about 6 cent (US) per kg and harvest costs are US$ 0.524 of which packaging material is US$ 0.496. At this point of the production cycle, one should decide whether to export in bulk, thus achieving lower prices, or whether to target the retail stores and pre-pack the date fruit in attractive “glove boxes”, achieving higher prices.
Operational cost per ha for a large commercial date plantation (US$)
(*) Labour includes weeding, pruning, pollination, thinning and orchard maintenance.
(**) Labour includes sorting, cleaning, de-stoning, packing and packing house maintenance.
The calculations in Table 63 for marketing costs are based on the assumption that 30 % of the harvest will be marketed locally and 70 % will be for the export market. Estimated marketing costs are in the order of US$ 0.86 per kg. In the calculations for transport to Europe, air transport is used only during the first two years of production. Air transport is quite expensive, but since volumes to be exported are low in the initial stages of production, sea transport cannot be considered. Total operational cost as outlined in Table 63 amounts to US$ 1.446 per kg (Naute Project during 1997).
Operational cost for a small date plantation (1 ha); (US$)
(*) Labour includes weeding, pruning, pollination, thinning and orchard maintenance.
(**) Labour includes sorting, cleaning, de-stoning, packing and packing house maintenance.
(***) Higher water cost for small date plantation due to the fact that water is usually supplied from a borehole and pumped with a diesel engine at high cost.
In this scenario the small scale producer will sort and grade the fruit, but sell in bulk to a packing house. As a result, the expensive activities, i. e. pre-packing and export, are covered by someone else. This strategy will reduce production cost from US$ 1.446 per kg to US$ 0.236 per kg. Obviously the price to be received will also be much lower, as will be the risks involved in exporting.
3.3 Cash flow statement.
The function of cash fl ow is to provide information on the timing and magnitude of cash (infl ows and outfl ows). Both cash fl ow statements here below summarise the cash fl ows for large (40 ha) and small scale (5 ha) date plantations, over a period of 10 years. For the calculations in Tables 65 and 66, the following average production potential per palm in kg is considered.
* For a well maintained large scale modern date plantation, production could start one year earlier than the small scale one and be over 100 kg/palm/year.
An estimated cashfl ow statement for the large scale modern date plantation is given in Table 65. The costs indicated are calculated as follows:
Cash flow statement for 40 ha date plantation (US$)
The Table 65 cash fl ow statement suggests that net income is positive only as of year six, while the accumulating balance is negative up to year nine. Total costs in year 10 totals to US$ 1.95 per kg. Although costs can be recovered over the 15- year period with proper production techniques, planning and management, attention should be focused to improve the cashfl ow situation in years 1 to 5.
Cash flow statement for 5 ha date plantation (US$)
10 30,000 30,000 3,480 26,520 82,783.
Analysing costs at a smaller scale (Table 66), it can be seen that operational costs can already be covered in the first year of production (year 5 after establishment). The accumulated balance, however, is only positive in year 6. In calculating the cashflow, an income of US$ 1 per kg is assumed, considering that financing management and administration costs are taken into account. Investment in a 5 ha date plantation might thus result in a net income of US$ 26,520 in year 10 with a yield of 50 kg per palm at US$ 1 per kg.
When comparing the cost of production of 1 kg of dates for a large scale modern plantation and that for a small producer, one would like to suggest that a nucleus-regional packing.
CHAPTER IX: DATE HARVESTING, PACKINGHOUSE MANAGEMENT AND MARKETING ASPECTS.
CHAPTER IX: DATE HARVESTING, PACKINGHOUSE MANAGEMENT AND MARKETING ASPECTS.
By Baruch “Buki” Glasner, A. Botes,
A. Zaid and J. Emmens.
Date Production is a world agricultural industry producing about 4,7 million tonnes of fruit in 1997 (FAO, 1998).The date fruit, which is produced largely in the hot arid regions of Southern Asia and North Africa, is marketed all over the world as a high value confectionery or fruit, and remains an extremely important subsistence crop in most of the desert regions.
In this chapter the main focus is on date harvesting, packinghouse management and marketing aspects for the purpose of selling the produce as whole dates. Other date palm products, mostly prepared from dates of lower quality than those sold as whole dates, are also described.
In their analysis of the essence of quality, all modern approaches focus on the client (the consumer), his perception of the product, and the behaviour of the product according to defi nite specifi cations. There is progressive improvement in the quality of the product in line with the rising expectations of clients. This process must be stable, repeatable and capable of producing identical qualities for any length of time.
People very often think of marketing as the activities which take place after the product leaves the production point. Marketing, however, involves more than just that and might be defi ned as the set of economic and behavioural activities that are involved in co-ordinating the various stages of economic activity from production to consumption (Purcell, 1979). It is important to note that the benefi ts of a year - long and outstanding job of production can be wiped out with a single bad marketing decision.
A farmer’s job does not begin and end with producing something. The first agricultural marketing job is thus to determine accurately and in quantitative and qualitative terms just what consumer demands are in time, place and form, and what changes are taking place in those demands over time. The more time, effort and money a fi rm spends in carefully and completely planning the product which it wants to produce, the less time it is likely to need to spend in selling.
Large amounts of money are being spent to produce the fruit. One should thus put in as much effort as possible to capitalise on the investment through marketing. Marketing is expensive, but to be successful one needs to invest and to be creative. Fresh dates are not something new on the European market. Therefore, to be able to sell the date fruit, the packaging should be more attractive, and the contents should be of a higher quality than the competitors’. Low input gives low output.
Profitability is also an important measure, making additional investments possible for improvement and growth. The approach is one of delegation of authority to the people who are at the heart of the production process; who may work according to well defi ned procedures and at the same time use their common sense and act judiciously. Emphasis is placed on cooperation between suppliers and clients in order to make it possible to work with precision, to receive feedback detecting mishaps, and to develop new products.
Emphasis has traditionally been placed on the commodity involved, or the economic functions performed, or the institutions that are involved in performing the various functions. Focusing on these issues separately is important, but the marketing strategy should be to adopt a marketing approach where emphasis is placed on the total system. With this, the entire continuum, from producer to consumer, becomes the focal point.
While describing the process which the fruit undergoes in the packinghouse, from the moment of entry until the product is ready for marketing, emphasis is given to the various aspects of quality control, mandatory in high quality products.
2. Harvesting considerations.
There are specifi c harvesting and packing considerations for each date variety and the form in which they will be consumed.
Harvesting means physically detaching the fruit from the palm. Differences in the state of the fruit, from the point of view of harvesting, are great at the level of spikelets, bunches and palms. These differences are both visible, such as the fruit colour and the degree of ripeness; and invisible, such as the percentage of water and of sugar and the activity of various enzymes.
Whole dates are harvested and marketed at three stages of their development. The choice for harvesting at one or another stage depends on varietal characteristics, climatological conditions and market demand.
The three stages are as follows:
Khalal: Physiological mature, hard and crisp, moisture content: 50 – 85 %, bright yellow or red in colour, perishable;
Rutab: Partially browned, reduced moisture content (30 – 45 %), fibres softened, perishable;
Tamar: Colour from amber to dark brown, moisture content further reduced (below 25 % down to 10% and less), texture from soft pliable to fi rm to hard, protected from insects it can be kept without special precautions over longer periods.
In general, when dates reach the Khalal stage, they are regarded to be ready for trading as “fresh” fruit. Dates in Khalal stage are the first in the harvesting season and therefore have aready market. Only date varieties with a low amount of tannin at Khalal stage are suitable for consumption. The low amount of tannin results in low astringency. Furthermore, it is important that the fruit is sweet and not bitter. Date varieties suitable for marketing at Khalal stage are Barhee, Zaghlool, Hayany and Khalas. Of these varieties, only Barhee is sold in England, France and Australia, while the other two are mostly consumed locally.
Experience in most date producing countries showed that a well matured Rutab, handled with care, is one, if not the most, appreciated form in which the dates is consumed and which gives the grower the highest rate of return. However, Rutab has three serious setbacks: it is produced in comparatively short periods with the tendency of production peaks; it is highly perishable; and it is delicate, which makes handling and transport diffi cult and expensive.
Major commercial date varieties harvested at Rutab stage are Deglet Nour and Medjool. Deglet Nour is harvested yearly in tens of thousands of tons in Algeria, Israel, Tunisia and the USA. The production of Medjool is more limited (less than 5,000 tons per year) and mostly produced in Coachella Valley and Bard in California, USA, Morocco and Israel. Small amounts are produced in Mexico, Namibia and South Africa.
Fruit harvested at Tamar stage is non-perishable, i. e. micro-organisms cannot grow on it, moisture uptake and its consequences, and changes in colour and taste occur during storage. Most of the dates of Dayri, Halawy, Khadrawy, Thoori, Zahidi, Sayer and Aliig varieties are harvested after the fruit has undergone the process of ripening and drying on the palms.
Fruit at the Tamar stage is ideal for marketing as “dried” datas. This fruit is used for preservation and year-round consumption and also for the production of various types of products, e. g. cakes, sauces and components of granules or date honey.
The main outlets for dates at the Tamar stage are the following:
• home consumption, local markets.
• wider regional distribution.
• collecting/bulk packing centres.
• small, medium, and large-scale packing plants for bulk shipments and retail packs.
The softening of the fruit is mainly infl uenced by polygalacturonase and cellulase enzymes. The activity of these enzymes depends on the slow drying of the fruit.
The invertase enzyme determines the speed and level of transition from disaccharid to two monosaccharids, fructose and glucose. These changes determine the speed of evaporation of water from the fruit. The level of fructose and glucose infl uences both the speed of drying and the activity of the polygalacturonase and cellulase, and also the relationship between the water activity Aw and the water content, and so the extent of shelf life. Water activity can be expressed by Equilibrium Moisture Content (EMC) expressed in percentages; the EMC expresses the sensitivity of the fruit to microbiological infestation. EMC below 65 % ensures resistance to microbiological factors such as moulds, yeast and bacteria that attack the fruit (Figure 87).
Although attempts are being made to harvest the fruit by shaking the trunk of the palm in order to avoid having to climb it, it is still necessary to reach the top of the palm to harvest the fruit. The palm grows up to one meter every year (depending on variety and the intensity of treatment). Harvesting the fruit entails the use of experienced workers, or investment in aluminium ladders, in attaching ladders to the palms permanently or in purchasing mechanical appliance to lift workers to the top of the palm (Figure 80).
Harvesting in the northern hemisphere takes place at the end of summer and in the fall, starting at the end of July (depending on the geographical area), with the harvesting of the Khalal varieties (especially Barhee), and ending in the middle of November. The harvesting of certain of the varieties continues after the rain starts (The end of summer rain in California, and the fall rain in North Africa and Israel). Rain can cause damage to the fruit and impair its quality due to rotting, fermentation and insect infestation. The fruit must therefore be protected against rain with the help of wax-covered paper or nylon sleeves. In the southern hemisphere harvesting takes place in February, March and April.
Harvesting must be faultless and clean, since it signifi cantly affects the rest of the process (packing and marketing). Harvesting the fruit straight into containers suitable for transport to the packinghouse prevents the infection of the fruit by the soil and sand under the palm and ensures that the fruit arrives in good condition, and that it is not crushed.
2.2 Field sorting of fruit.
In 1997 the world production of dates was 4.7 million tons (FAO, 1998). Much of this fruit is still grown and processed by traditional methods described in great detail by Dowson (1962). These methods involve mainly the drying and curing or ripening of the fruits (which have been laid out on cloths or mats) in the sun, pitting (destoning) by hand and storing in jars.
The harvested fruit is transferred into containers (large plastic bins) for transport to the packing station. Each container contains 200 – 450 kg fruit and is suitable for dry fruit. Large wooden, plastic or cardboard cases of various sizes are also used, focusing on the need to prevent damage to the fruit (especially to soft and sensitive fruit). Baskets and sacks (for very dry fruit), as well as trays are also used. It is desirable to separate damaged fruit which is not destined for the market, while still at the site. Dates that are rotten, sour, with remains of insects, crushed, shrivelled up, unfertilized, or unripe fruit which are not intended for artifi cial ripening should be removed from the plantation. These fruits should be destroyed or fed to animals, in order to maintain sanitation of the plantation.
2.3 Transporting to the packinghouse.
When transporting the fruit we must also take into account its sensitivity, and the importance of every link in the chain in the treatment of the fruit. Dates harvested at the Khalal stage must be transported as soon as possible to receive appropriate treatment, whether it is Barhee, Khalas, Hayany or Zaghlool for local consumption or for export. The fruit must be transported in the early hours of the morning to avoid the heat; if the distance is great, refrigeration during transport is advisable. Deglet Nour, which is to be marketed on the branches must not beshaken during transportation in order to prevent the fruit from falling off the branches. Speedy transport will also prevent infection by pests which attack the fruit during the post - harvesting period.
2.4 Quality control on the use of chemicals.
Many clients, especially from European markets, demand that the quality control processes used be documented by the growers; especially a report concerning treatment (spraying) against insects. Such a report includes a list of the materials permitted for use and approved by an offi cial agent, in addition to the timetable of the spraying with details of materials used, the date, concentration, number of days before harvesting and the level of residue of pesticides; the level permitted appears in the Codex Alimentarius published by FAO. This book gives the permitted level MRL (minimum residue limit) according to types of material and species of fruit, vegetables and other foodstuffs. Today, it is possible to reach a level of detection of such remains at PPB (part per billion), but the cost of the test is considerable.
3. Facilities and process.
Packing is a vital stage in both the traditional and modern methods of marketing. At this stage many varieties of varying quality, water level and rate of pest infestation can be preserved up to a year. The aims of packing are:
a) To make it possible to transport the fruit by various means: from baskets made of palm leafl ets, to the use of modern packing containers, and transport by air or by sea in containers. The sturdiness of the packing must be adapted to the methods of transport.
b) To protect the fruit when packed so that it will remain in good condition under various circumstances and for various periods of time. The packing materials should be chosen according to the quality of the fruit as required by international standards or consumer needs (e. g. it is forbidden to use PVC). Packing must preserve the moisture of the fruit, prevent further drying out of the fruit and any loss of moisture in moist fruit. It must withstand conditions during storage (there are materials which do not withstand a temperature of – 18o C). The packing must preserve the fruit for as long as necessary.
c) To use packing in order to promote marketing. Some of the data on the packages are relevant to the laws in the importing countries; some provide information for the client and some serve the promotion of sales, or as labelling (such as EAT ME for Deglet Nour or CALIFORNIA DATES, or KING SOLOMON for American and Israeli Medjool, respectively). In most importing countries, the law demands that data such as weight, country of origin, quality and date of expiry, appear on the package.
In various countries there are several kinds of contracts between growers and the packinghouse. Family packinghouses may be small or large, built in or near the plantation, and they are owned by the grower. In such a packinghouse there is continuity and coordination between the activities at the plantation and in the packinghouse. Workers at the plantation supply thefruit in accordance with the potential of the packinghouse and the relevant installations to receive it, for instance for fumigation, refrigeration and storage. The packinghouse also adapts itself to the constraints of harvesting, such as the speed of ripening of varieties harvested at the Khalal stage, adding another shift when necessary, increasing its workforce (temporarily), renting storage space and operating fumigation rooms continuously.
Cooperative packinghouses are set up to exploit the advantage of size; growers get organised according to a specific region or fruit variety (especially for the packing of Deglet Nour on branches). These packinghouses usually accept fruit according to one of the following methods:
a) By keeping the fruit from each grower separate during all stages. To do this, labels (with the grower’s number) are put on the crates (or any other packaging) at entry, during fumigation and storage, and during sorting and packing. One can also separate the fruit from different growers by storing it in different labelled areas or packing it on different days.
b) By sampling the fruit at entry. After sampling the fruit is separated according to the management, production and marketing needs (not according to suppliers).
Private packinghouses usually buy the fruit as raw material directly from growers. This has the following advantages:
* The grower is paid immediately for the crop.
* The packinghouse can sometimes acquire the fruit at a competitive price.
* The packinghouse functions independently of the grower after the purchase.
* The grower usually receives a lower price, since all the risks are transferred to the packing-house.
* The packinghouse may not receive good quality fruit.
Sub-contracted packinghouses usually receive the fruit after it has already undergone several processes, especially fumigation and preliminary sorting. These packinghouses are not always in the area or country where the fruit is grown. Some of them specialise in small scale packaging, directly connected to the marketing networks; they defi ne the desirable quality to the supplier and check the fruit at entry according to the required criteria.
3.2 Processes used to improve or maintain fruit quality.
In the packinghouse there are a number of processes, designed to improve or maintain fruit quality. These processes are: fumigation, washing, storage, refrigeration, hydration, dehydration and curing.
In order to store the fruit for a long period (several months to one year), it must be completely cleaned of any pests (eggs, pupas, larva or adults). This is done by fumigation, either in the fi eld under various kinds of plastic sheets, or at the packinghouse in special sealed rooms.
Fumigation must not be carried out when the fruit is fresh, harvested at the Khalal stage, (Barhee, Khalas, Zaghlool and Hayany) or when stored under deep refrigeration. The substance most frequently used for fumigation is methyl bromide (CH3 Br), which makes most of the insects come out before they are killed by the gas. The concentration of the gas is 30 ppm, i. e. 30 g methyl bromide in 1 m3 of air. The time recommended for fumigation is 12 – 24 horas. The temperature must be above 16o C. It is important for the air to swirl within the fumigation installation, in order for it to spread uniformly within the chamber.
Methyl bromide is a dangerous poison. This fumigation process must, therefore, be done according to the law and all the regulations concerning the equipment and the protection of the people involved.
After fumigation the chambers must be aired according to the producers’ instruções. The level of fumigation described above kills insects, while keeping within the level of remains at the MRL, permitted according to the Codex Alimentarius (FAO). After fumigation the fruit must be stored under conditions that prevent re-infestation. It is therefore undesirable to store fumigated fruit together with unfumigated one.
Additional substances and methods are also being used, for instance irradiation by gamma rays or exposure to ozone. For dates grown and marketed by the bio-organic method, can be used. fumigation by CO2.
It should be noted that in 1992 methyl bromide was placed under the Montreal Protocol on substances that deplete the ozone layer, because of international concern about the continued increase in its production and its damaging effect on the ozone layer. Actions taken by countries party to the Montreal Protocol are:
* Limitations on an increase in the production of methyl bromide from 1995, and.
* Consideration of longer-term options to completely phase out its use.
At the moment there are no restrictions on the import/export of methyl bromide treated products. Restrictions on the import/export of these products were postponed till the year 2003. The latest information can be obtained from the UNEP Secretariat to the Montreal Protocol.
Alternatives for methyl bromide:
* Phosphine is the principal alternative to methyl bromide for fumigation of durable commodities and is widely used in developing countries.
* Controlled atmospheres high in carbon dioxide are in regular use in South East Asia for disinfecting bag-stacked durable commodities.
* The applications of physical control methods such as fi ltering, heating or cooling regimes, active oxygen (ozone, hydrogen peroxide) and irradiation. However, some of these methods are very costly (CBI, 1997/1).
3.2.2 Storage and refrigeration.
After packing, the fruit will be sent according to market orders, or stored as the fi nished product. During storage, the material in which the fruit is packed must also be taken into account, for example: cardboard is sensitive to humidity; various plastics are sensitive to low temperatures; wooden surfaces may be attacked by various pests.
In the storehouses the produce must be protected from recontamination by pests (insects and rodents). The surfaces and packages must be well made in order to withstand being loaded, shaken on the way and unloaded.
The aim of storage is to attain the state of DQ = 0 for a long period (Q = quality; D = variation), which means creating a situation in which the quality of the fruit does not change during storage.
Much of the fruit is marketed throughout the year (especially fruit at the Tamar stage), and sometimes even after a year has passed, because of the need to prepare the fruit for Christian festivals, or at times when the Muslim Feast of Holy Ramadan is close to harvest time.
According to traditional methods, the fruit is protected from external hazards and preserved by being dried to a level of moisture that will ensure that it is not sensitive to microbiological contamination even in ambient temperatures, or by being pressed into sealed baskets or jars.
The current market demands fruit with higher moisture content. Preservation is ensured by storage under low temperatures. The temperature at which the fruit is stored is adapted to the time lag until the next treatment or until marketing. The temperature must ensure the continued extermination of insects that have survived fumigation, and prevent loss of moisture, or in the case of dry fruit, increase the moisture. Refrigeration must not infl uence properties, such as texture, moisture and colour.
The temperature and the speed of refrigeration also affect physiological phenomena, such as sugar crystallisation. Sugar crystallisation is caused by the breaking of cell walls or the tearing of the skin, facilitating the movement of water inside the fruit or out of it. This is connected to the amount of moisture in the fruit. The risk increases when the amount of moisture rises above 20 % (also in low temperatures). This phenomenon does not exist in Deglet Nour. Today, the temperature commonly used for long-term preservation of dates of several varieties including Medjool is – 18o C (0o F). This temperature decreases possible water loss and also decreases the sugar crystallisation and skin separation phenomena.
However, research done in Tunisia showed that:
* storage under conditions of 26 % humidity or higher requires a temperature of 0ºC enabling a storage period of 6 – 8 months;
* the storage period can be more than 1 - year if humidity is less than 26 %;
* if humidity is less than 20 %, dates can be stored at 25ºC for up to 1- year; e.
* high sugar content coupled to high humidity tends to aggravate the situation of fruit going bad.
Varieties sold at Khalal stage, such as Barhee and Zaghlool, are stored at a temperature of 1°C, which increases their shelf life from a few weeks up to 6 – 8 weeks.
Just like all agricultural products, dates are grown in the fi eld and exposed to various types of contamination of physical, chemical or/and microbiological nature.
Physical factors: Sand and soil – both as a result of sand storms in many regions where dates are grown, and soil sticking to fruit lying on the ground.
Chemical factors: These are especially remnants of pesticides, some of which can be removed by washing.
Microbiological factors: External cleaning of the fruit by washing removes some of the microbiological pollution, also excretions of birds, which may spoil the fruit (Figure 81).
Clean water must be used and care taken that all the fruit is washed. Other methods exist, such as damp towelling attached to sloping mechanical shakers (California – USA). The fruit from Barhee and Deglet Nour are also cleaned by air pressure specially adapted for the removal of dust and sand, before they are packed on branches. While the fruit is still hanging, it can be cleaned by water spray, accompanied by the use of fine swivelling brushes, but they must be dried before being packed.
When the fruit is packed immediately after washing, it is important to dry it in drying cubicles or by means of large fans.
3.2.4 Hydration, curing and dehydration.
The aim of dehydration and hydration is to improve the quality of the fruit, to produce uniform fruit with regard to moisture, and to extend its durability during storage and marketing. These processes are carried out by artifi cial means in the packinghouse when hydration or dehydration are not carried out earlier, during the treatment of the fruit in the field. When treated in the packinghouse, the fruit is dehydrated or hydrated after it has been stored or washed, when the moisture can range from 10 % in very dry fruit to 30-45 % in fruit at the stage of curing (Rutab). Of course, the moisture of the fruit also depends on variety, the region and the weather at the time of harvesting.
Some varieties (for example Amri and Zahidi) have a dry and hard texture in regions where, during the ripening of the fruit (the transition from Khalal to Rutab and from Rutab to Tamar), the temperature is high and moisture is low. In this situation moisture must be increased by hydration. This is a process of fruit saturation with water or steam, while ensuring the appropriate temperature in order to create optimal conditions for enzymatic activity, which will cause the fruit to soften. This softening is often accompanied by a rise in moisture to a level that can endanger the fruit by exposing it to microbiological elements (when moisture reaches over 20 % and EMC over 65 %). The appropriate hydration process depends on how long the dates have been exposed to these conditions.
An activity similar to hydration, by integrating temperature and moisture, is carried out when some of the dates are unripe, Khalal, or when a stage has been “skipped”. Unripe fruit enters the packinghouse for two reasons:
* In cold regions (for example Elche in Spain) where the fruit does not ripen under natural conditions, or rain may threaten the fruit.
* When harvested in the usual way (Khalal).
“Skipping a stage”: This situation arises when the transition from Khalal to Tamar is very fast (in hot regions) and some of the fruit is not ripe while the fruit is already shrivelling and at the Tamar stage. Such dates (usually of the Medjool variety) have white shoulders or are naturally white – these are the parts of the fruit in a light unripe state against a light brown background of Tamar. Most of the Deglet Nour in California is harvested when it is very dry and hard, and only hydration treatments bring it to a moisture of 23 to 25 %, and make it suitable for marketing (to meet consumer demands).
Dehydration is undertaken when the moisture of the fruit is higher than planned (with respect to market needs). In order to preserve the fruit for any length of time (without refrigeration), it is important to decrease the moisture to below 20 % (depending on variety). At a moisture percentage of 15 % to 20 %, varieties such as Khadrawy, Halawy and Medjool can be preserved for a long time, unharmed by microbiological processes (such as fermentation, souring or the emergence of mould). If the moisture percentage is too low, the fruit will be hard to eat and inappropriate for some of the consumers (mainly on the European market). Decreasing the moisture also reduces the risk of sugar crystallisation.
It is important to ensure moisture uniformity. Fruit at an undesirable level of moisture will be spoilt by microbiological processes. This phenomenon is found in “Juicy Medjool” and in Deglet Nour on branches, when packed with a high level of moisture. First, alcoholic fermentation takes place as a result of yeast activity, and later a process of souring, caused by the activity of various kinds of lactobacilli. The following factors infl uence appropriate dehydration: temperature, moisture, speed of airfl ow, uniformity of the above variables and length of dehydration time.
Dehydration is carried out in special chambers. These chambers control the entry and fl ow of hot air, to ensure the appropriate moisture level. All these conditions must preserve the quality of the fruit, especially with regard to skin separation. The temperature must not rise above 70oC in order to prevent “the burning of sugars” (caramelisation). High temperatures will also cause the fruit to darken. Different temperatures suit different date varieties: Halawy 55oC (and 20 % moisture during the process); Deglet Nour and Medjool 50oC.
Quality control during hydration and dehydration.
The amount of water in the fruit exerts a great infl uence on its quality and shelf life. It is mandatory to have a constant follow-up on the product by various means of testing. This is to ensure that the client receives fruit of the quality he or she requires, both with regard to softness and to moisture, which must not be too high. The latter prevents harmful microbiological processes and the rise of sugars.
An important aspect of quality control is the documentation of the findings, making it possible to check the amount of moisture during the various processes and facilitate the traceability of the product, which is important for the detection of mishaps during the various stages of production.
In order to ensure that the results of sorting are appropriate to client requirements, it is important to provide sorters with precise, unambiguous defi nitions of the defects of the fruit they are to transfer to another category. The following defects can be identifi ed in date fruits:
1. Defects stemming from microbiological processes: fermentation (alcoholic) resulting from the activity of yeast; souring resulting from lactobacilli, acetobacteri or aspergilus niger, a fungus which creates a black promycelium which fi lls up the stone cavity. These types of defects cannot be tolerated, such fruit must not reach the customer, nor can it serve as raw material for products. These defects may be due to inappropriate conditions during storage (for example wet fruit without refrigeration) or may arise while the fruit is still in the fi eld.
2. Defects caused by pests, resulting from the activity of insects and various mites. The most common are the remains of various moths, sour bugs and mites. Some of these pests leave signs of nibbling inside the fruit; some spoil the look of the skin. Tolerance for these defects differs according to various standards, going up to 4 %; in all cases there must be no live insects inside the package. Defects caused by birds, mice, bats or other rodents (mainly signs of nibbling on the outside) are often found on fruit grown without being covered by a net or paper, or stored under inappropriate conditions. Such fruit must be removed. These pests may leave remains of feathers, excrement of mice or birds, which stick to the fruit and may cause microbiological contamination.
3. Mechanical defects, as a result of the fruit being crushed while wet after harvesting, or grazed or scraped during the period of growth, leaving scars on the fruit. Sometimes the fruit is so badly soiled by earth and by mud that washing does not clean it.
4. Physiological defects:
* Unpollinated fruit that reaches sorting in an unripe state (its colour depending on the variety);
* Shriveled and dry dates, usually dates which have been detached from the spikelet while still unripe;
* Defects caused by water stress (excess or shortage), which may lead to checking (in Barhee) or blacknose.
Some defects will appear more frequently in certain species. Workers must become familiar with them. This information can be provided by drawings of the defects, and there must be guidance during the sorting and control of its results (Figure 82).
Quality control during sorting.
Control and sampling is done by laboratory workers. Control must ensure that the demands of the sorting instructions and defi nitions have been respected. Testing for internal defects is done by cutting the fruit with a knife and checking the internal cavity. Sampling is carried out according to procedures defi ning the frequency of sampling and the size of the sample. The results are written on a specifi c form, and the forms are kept for the follow-up according to the demands of clients.
The clients are the buyers whose quality system demands that the suppliers have authorization, either via an acknowledged certifying body, or according to client specifi cation, which includes documented traceability.
This is usually done together with sorting, on the same installation, thus avoiding the need to transfer to a different storage (at the intermediate stages) and additional pouring of fruit onto the conveyer belt. Many attempts have been made to make this process more effi cient by automatic grading, but, owing to the complexity of the processes and the diffi culty of imitating human senses, especially that of sight, no solution has yet been found for sorting and grading “without human hands”.
The aim of grading is to produce packed fruit which is uniform in size, shape, colour, texture, moisture and skin separation. For each variety the standards are different. Client’s requirements can also determine the criteria during grading:
Size sorting can be done in one or two stages.
• Grade A: Perfect fruit.
• Grade B: Fruit with skin separation.
• Grade C: Fruit for pitting and for industrial use.
• Grade D: Rotten and damaged fruit.
The second stage of sorting is to sort the grade A product to size (jumbo, large and medium). This is particularly important for varieties with large fruit such as Medjool or Amri. For Medjool in Israel, sizes have been defi ned according to the weight of the fruit (moisture content fi xed at 16 % – 19 %):
Jumbo: more than 23 g;
Large: 18 g to 23 g; e.
In other countries (for instance USA) other defi nitions of size are used. Varieties with a certain texture can be mechanically sorted for size using a sorting machine on the basis of rollers, the diverging roller sizer. This machine is suitable for sorting species such as Amri, Zahidi, Deglet Nour and Hayany.
A uniform shape, typical for each variety, is required. Abnormal or misshaped fruit is removed. Regarding colour, one variety may have different colours depending on the way it was grown, the time of harvesting and the region. Texture depends mainly on the moisture content, but also on normal ripening which activates enzymes softening the fruit. Moisture must be appropriate to client requirements, to the date of marketing and to the conditions of storage.
Reasons for skin separation, also called puffi ng phenomenon, are still not known. During certain years, especially when it is relatively hot, the rate of fruit puffi ng is higher. Such fruit has not gone bad, but it is unsightly, especially when skin separation is extensive. The fruit lacks uniformity and its appearance is impaired. This phenomenon also differs in extent according to the region where the fruit is grown. It is more serious in varieties such as Medjool, signifi cantly lowering the price for export fruit.
Quality considerations during selection.
It is important to make use of the laboratory at this stage; some of the criteria are quantitative and can be assessed objectively (unlike tests by human senses), and the tests are carried out according to defi nite standards, set by the importing countries or the customers.
It is important to document the tests and include the dates when they took place, their results, their Lot number or ID and deviation from the standard, corrective action (if necessary) and the signature of the authorised person. This ensures that the results conform.
to the standard required and that any deviations can be treated. The laboratory and the people responsible for quality must have the authority (granted by regulations) to stop the process when its products are inadequate.
Fresh dates are perishable and are highly susceptible to losses from damage and deterioration between harvest and the fi nal consumer. Within the range of measures which can be applied to prevent such mechanical and/or biologically induced losses, appropriate packaging plays a vital role in protecting produce from avoidable deterioration.
Packing the fruit in various ways is the last stage of its preparation for the consumer. Therefore, there is no contact with the fruit itself, and we depend on packaging to protect, contain and market the product. Various methods of packing, including the traditional ways, are already described in detail by Dowson (1962). In this section we shall only relate to modern methods used for fruit intended mainly for export. The methods of packing are of two kinds: in bulk and for retail sales.
The dates are usually packed in cardboard boxes (sometimes in plastic bags for additional protection and preservation of moisture, before being placed in boxes). The usual weight is 5 kg or 15 lbs. (depending on the country where the fruit was produced or where it is to be marketed). The quality of the fruit may differ according to customer requirements. The fruit is sold on the open market and intended for customers wanting to buy fruit in large quantities. The fruit may be handed over to be repacked in the countries where it is to be marketed and where retail packing will be carried out according to the customer requirements.
The fruit may also be used for products in which dates are the main or secondary component, such as sauces, syrups, spreads and products used in baking.
Retail packing has been greatly developed in recent years, especially since the large networks have increased their share of the food market throughout the world. These packages have to be adapted to consumer demands at all levels, starting with the codes used by a certain network, to repackaging and to the surface on which they are to be placed, ending with the writing on the packages such as the nutritional composition, and the last date for sale or for use.
Retail packages can be divided into two categories:
a) Packing according to some arrangement, usually ‘fi sh bone’, the traditional way, which was developed in Marseilles in France and is called ‘glove box’ or ‘boite à gants’ in French. There are usually 26 – 30 dates in this box, placed in two layers, separated by cellophane, weighing 220 g – 250 g. A natural or plastic spikelet is placed in the top layer. Most of the dates in such boxes are sold at Christmas time under various names. The variety most commonly used is Deglet Nour, but other varieties can also be found. Packing is done manually and much time is invested in arranging the dates in the boxes. The fruit is usually covered with glucose (natural) to give it a shine appearance.
b) Packing by automatic weighing (without any inner arrangement): Much packing is done in this way, starting with the ‘window’ type, where a cellophane window showing the fruit is part of the package design, which is usually made of cardboard.
Dates are also packed into tubs made of transparent plastic, showing the fruit as part of the package design. The information for the client is usually on the lid. This type of packing can be of varying sizes, according to the client demands. Bags, usually made of PET polyethylene, are the cheapest and most economical way of packing.
Many attempts are being made to introduce mechanisation and automation in order to save on packing and weighing. In recent years computerised combinatorial scales have been developed, making it possible to pack exact quantities, combined with automatic packing machines for many types of packages.
Quality considerations during packing.
Quality control of packed products is the last time the fruit is checked before reaching the customer. Documented checking of the packages entails:
* weight of the package;
* weight of the fruit;
* arrangement of the fruit (in glove boxes);
* uniformity of the fruit;
* damage to the fruit;
The surrounding area is also checked:
* cleanliness of the conveyer belts;
* calibration of the scales (automatic or manual);
* writing on the packages;
* satisfactory working of the metal detector (installed on every retail packing line);
* repackaging installations and marking; e.
* qualifi cation for international standards such as ISO and HACCP (details follow in para. 6.2).
Although modern management takes marketing into consideration at all stages of production, in actual practice the shipment of the fruit takes it away from the region of the supplier and places it at the disposal of the market. All shipments are carried out according to the planning and direction of both the local and the export markets. Ttypes of shipment (relating mainly to export) are:
* shipment by sea; * overland and sea shipment combined; and, * shipment by air.
It is advisable to choose the cheapest transport which will bring the fruit to the client with DQ = 0 and at the right time. (DQ = 0: The fruit must not be damaged during shipment. It must be protected physically and kept at the appropriate temperature). The cheapest alternative makes it possible to compete against other suppliers and saves on expenses.
The appropriate time for shipment sometimes forces us to use more expensive transport in order to satisfy client requirements. For example, at the beginning of the season, in order to get in before other suppliers, or sensitive fruit such as Barhee when being shipped over great distances.
Overland transport to markets where this is possible. The fruit must be transported in a way that will protect it from the environment and, if necessary, in refrigerated trucks.
Shipment by sea in containers, an effi cient and (relatively) cheap means of transport; the fruit is protected from the environment from the moment it leaves the producer to the moment it reaches the customer’s door. The containers are refrigerated (if refrigerated containers are used) by cold air fl owing horizontally over the layers of fruit. This air is distributed uniformly throughout the container.
Overland and sea shipment combined refrigerated trucks go from the supplier to a port where it is loaded to a ship that will transport the product further to its destination. This method is more expensive than shipment in containers (in the Mediterranean area and in Europe), but it is usually faster.
Shipment by air is the most expensive, but it is sometimes inevitable when the fruit must be supplied at short intervals. Transport to and from the airport must also be taken into account.
Documentation All the shipments must be documented in detail to ensure speedy transfer to the client (especially during export); beside documents for the customs, payment and transport, it is important to add a phytosanitary certifi cate stating that the fruit is healthy. This document is issued in every country by the relevant authorities and certifi es that the fruit is not infected by pests or diseases and is appropriate to the standards of the importing country.
Quality considerations during shipment.
Sometimes the fruit is stored for a long time before shipment (up to several months). Owing to marketing conditions and packing possibilities, it is necessary to sample each consignment, in order to make sure that the quality of the fruit has not changed. During loading it is important to ensure that the surfaces or packaging are not damaged. All the labels and markings must be checked according to the requirements of the law and of the customer in the importing country.
Temperature recorder: Since temperature is an important factor in the preservation of the quality of the fruit, especially for fresh dates at Khalal or Rutab stage, a temperature recorder must be placed in the container, the truck or on the surface. This is a small mechanically operated unit. After the details of the shipment have been entered and the unit has been turned on, it records (on a ribbon) the necessary information about temperature during the shipment. The customer will only sign the receipt for the shipment if the temperature corresponds to the demands which were defi ned for the carrier.
4. Harvesting and packaging consideration for some important commercial date varieties.
This variety is harvested and consumed at an unripe yellow stage (Khalal). The fruit is locally marketed on branches or exported on branches in cardboard boxes. This way of marketing and consumption requires harvesting of the bunches in a state of Khalal before it turns into Rutab, and without any green fruit. Barhee can be consumed in this state owing to the low amount of tannin, which becomes non-soluble, and as a result the fruit is yellow Khalal with low astringency. It is also important that the fruit be sweet (not bitter) with a brix above 29. The timing of the harvesting of Barhee is very important to ensure that the fruit reaches customers in an unripe state. Whole bunches are harvested at the appropriate stage of ripeness. The harvesting of the bunch is carried out with a secateur or special knife, the heavy bunches (approx. 20 kg) are carefully lowered to the ground and placed on a clean platform or hung on a special hanger (Figure 84) and directly transported to the packinghouse. The harvesting is implemented in 3 to 5 rounds and only bunches in the appropriate state are cut off each time.
This variety (like Deglet Nour on branches) requires the combining of sorting with packing. The high moisture content of the date fruit at Khalal stage makes it necessary to shorten the time spent in packing and to keep the fruit at the appropriate temperature.
The fruit is packed on branches in cardboard boxes weighing 5 kg (in Jordan, Israel, USA and Saudi Arabia) (Figure 85). Green or ripe dates (Rutab) must be removed from the branches and only smooth, clean, yellow dates are packed. Since the fruit is fresh, the temperature must be lowered immediately after packing. It is also important to keep the fruit aired in order to remove substances, such as achetaldhide ethylene and CO2.
Characteristics of the fruit.
Unripe, yellow, clean, smooth, hard without scratches, the fruit attached to the branches; diameter 26 mm minimum.
Branches at least 10 cm long and at least 5 dates for every 10 cm.
No tolerance of live insects: the fruit is not fumigated.
Tolerance of green fruit: 1 % (of the number of dates).
Tolerance of cured fruit: 1 % (of the number of dates).
Detached fruit in the box: 3 % (of the number of dates).
Storage temperature: 1 °C.
Transport temperature: 1 – 5 °C.
Deglet Nour is marketed and consumed in two main ways, infl uencing considerations at the time of harvesting:
a) Harvesting the fruit on branches: tens of thousands of tons are harvested in this way in Algeria, Tunisia and Israel, where it is consumed but also exported, mainly to France, Spain and Italy. When marketed in this state, the fruit must be soft and juicy, but with a potential shelf life of several weeks. The bunches are harvested when most of the fruit is in a state of Rutab, before they become Tamar, with a few Khalal. Fruit turning from yellow Khalal to Rutab will ripen between harvesting and consumption, during transport.
The bunches are lowered carefully and placed in containers or on some other device, and transported to the packinghouse. In most cases the bunches are wrapped up in a net to protect them from pests or birds, or in waxed paper or nylon sleeves for protection against rain. It is important not to shake the bunch in order to keep the fruit from falling.
Harvesting is carried out in 3 to 5 rounds and at intervals of 5 to 7 days, until all the bunches have been cut off the palms. Bunches which have a low percentage of fruit but which are suitable for marketing are shaken from the bunch and marketed in a different way.
b) Harvesting loose fruits to be sold unattached: harvesting is done palm by palm and the fruit must be at the Tamar stage. This method is used for all Deglet Nour in the USA and for Deg-let Nour in other countries when it is to be marketed over a period of time. Since this fruit is subjected to hydration treatment, it can remain on the palm until all the fruit is at the same stage of ripeness and dryness. When harvesting is carried out, it is important to protect the fruit from rain, which causes rotting and fermentation, and from various pests.
Treatment of Deglet Nour in the packinghouse.
A large part of the Deglet Nour crop grown throughout the world (in Tunisia, Algeria and parts of Israel) is marketed and consumed as Deglet Nour on branches. This product calls for special treatment, different from that described so far. Frequently, and mainly for fear of rain, bunches of Deglet Nour are harvested before they are completely ripe (at the stage of transition from Khalal to Rutab and the beginning of Tamar). Much of the fruit which has not ripened, ripens after it is harvested (fruit which is at the unripe stage, from red to yellow). These bunches are placed in aired containers or hung in large sheds (in Tunisia) and are kept for a certain period. This makes it possible to pack a larger percentage of the fruit.
The fl ow chart presented in Figure 86 describes the stages in the treatment of Deglet Nour for export (North Africa).
Various sorting systems are built in a way that makes it possible to perform several operations along the way and sometimes even to reach the fi nal stage of packing.
Packing Deglet Nour on branches.
At first, all the packing for Europe was done in a packinghouse in the region near Marseilles, but in recent years it is carried out in the countries where the dates are grown. A telescopic cardboard box is used (it has a bottom and a lid), and the weight is 5 kg. The packages are decorated with pictures showing bunches of Deglet Nour or date palms.
The fruit is packed from hanging frames in sheds or from containers brought in from the fi eld. The branches suitable for marketing are cut and packed in rows along the length of the cardboard box. The size of the box is usually 50 × 30 cm and it is adapted so it can be stacked on a standard pallet of 120 × 100 cm. Transparent cellophane is placed on top of the fruit and the lid is closed using pressure to avoid reinfestation or moisture loss.
The standards for this product were set mainly by the Tunisians and the Algerians and adopted by importers and other suppliers (as in Israel). The fruit must be soft and juicy, preferably of a light colour and with a transparent look. In good Deglet Nour the seed can be seen when the fruit is held against the light. The fruit is attached to the branch and must be clean; the moisture must not rise above 26 %. Each branch is more than 10 cm long and for every 10 cm there are at least 5 dates. There should be no more than 1 % of green fruit and no more than 1 % of unripe fruit (Khalal stage). Unsuitable dry, rotten and unripe fruit is removed from the branches. Live insects are not tolerated; the fruit is fumigated by methyl bromide on entering the packing installation. It must not be covered with dust or sand; it is best cleaned by air pressure. Detached fruit should not amount to more than 3 % in the box. There is no defi nite standard size, but the desirable weight per fruit is more than 8.50 g.
Deglet Nour on branches offers two alternative packages:
* Bunches: the fruit is packed in long cardboard boxes containing 2 bunches, with a total weight of 10 kg. The quality required is identical to that of fruit packed in 5 kg boxes.
* Bouquets: 3 to 5 branches are packed in a cellophane bag on a little cardboard tray; the branches are tied at their base. This pack weighs 200 to 400 g and packaging is labour intensive. The quality of the fruit is identical to that in the 5 kg boxes.
Quality considerations in packing Deglet Nour.
Since the texture of this fruit is unique, the soft and juicy textures are to be taken into account. It is also very important to ensure that there is no sand or dust on the fruit, and that its weight when packed is correct. During packing, storage and shipment conditions must be appropriate because the fruit is sensitive and goes bad quickly (mainly by souring); it is best kept at a temperature of 0 – 4oC. Freezing will cause the fruit to darken.
Most of the Medjool (less than 5,000 tons per year) is produced in the Coachella Valley and Bard in California, and in Israel, and additional small amounts in Mexico and South Africa. When harvesting this variety, clients’ wishes (large soft fruit with a moisture content of about 20 to 26 percent) are also taken into account. Medjool is a soft and delicate fruit with a thin skin, requiring careful treatment. Harming the skin may cause sugar crystallisation. In a hot climate (such as at Bard in California and in southern Israel) harvesting begins by picking the dates one by one at the beginning of the ripening process, at the transition stage from Khalal to Rutab. The fruit which has remained on the palm will become too hard to satisfy the needs of customers. In less hot areas, besides the wish for fruit with a soft texture, the need to protect the fruits must also be taken into account. When the drying process is slow, the fruit is sensitive to fermentation bugs - carpopilus. The Medjool fruit dries slowly because of the relationship between volume and outside surface.
The harvesting method is planned in such a way as to ensure that the fruit has the appropriate texture when it reaches the market. It must be soft, elastic, so it can be packed and preserved without changing shape. Its moisture should be 20 % to 26 % (when fresh), with Equilibrium Moisture Content (also called Aw-water activity) of not more than 65 %. In this respect, EMC is very important, owing to the relatively high water content. Harvesting will therefore take place while the fruit has a relatively high water content in order to prevent the fruit from losing water and becoming hard in texture.
The demand is for large fruit (over 20 g) where no skin separation or blooming is taking place, with a soft texture, and colour ranging from light to dark brown. by timely and accurate thinning, appropriate irrigation and fertilisation (see Chapters VI, VII and VIII). The colour of the fruit is (probably) due to certain soil and climate related factors, not under the grower’s control.
To make harvesting easy to handle, the worker is brought within reach of the bunch on a platform. Each bunch is then shaken gently to remove only ripe fruit i. e. those in the Rutab stage and at the beginning of transition to Tamar. The fruit is placed on shallow trays in a single layer.
Every bunch is harvested according to its state of ripeness, but it is important (especially in a hot climate) to begin when the ripe fruit is still soft; checking the fruit every fi ve to seven days makes it possible to harvest in an optimal condition, and prevents the fruit from being attacked by moths and nitidulid beetles. In regions where it is less hot the rounds can be made less frequently, keeping in mind that the fruit must be harvested before it dries. In some areas harvesting can also be carried out by selecting bunches with fruit that have passed from the Khalal to the Rutab stage; in this case some of the fruit will be at the Tamar stage.
The Medjool fruit falls off easily at the Rutab stage and the bunch is therefore wrapped up in a shade net (in Israel) or a cloth bag (in Bard, USA). The cover is open at the bottom and the ripe fruit is picked carefully from underneath through the openings, and placed on trays. This type of harvesting is very labour-intensive and costly; however at present the high price fetched by this fruit justifi es the process.
Field sorting Medjool.
In order to preserve the softness of the fruit after harvesting, as described in the previous section, several rules must be respected: the fruit must be soft in texture but with a moisture content that will make it possible to pack and store it for a long time.
In order to preserve the softness of the fruit (together with the other criteria) it is necessary to obey certain rules while the fruit is being treated on site:
* Only fruit which has reached the Rutab stage but not yet the Tamar stage should be harvested.
* Fruit harvested at different levels of moisture content should be separated.
* Each section should be dried uniformly to 20 – 26 % of moisture content or according to EMC to the level of 65 – 70 %. (Figure 87)
* The dried fruit should be kept under conditions which will prevent further water loss (sealing and appropriate temperature).
Drying takes place on trays in one layer; spread out in the sun or on platforms or in drying ovens, depending on the climatic conditions at the time of harvesting and on technological solutions (Figure 88).
4.4. Harvesting other varieties.
Beside Barhee, Deglet Nour and Medjool, the other varieties are harvested when all the dates in the bunch or even on the whole palm have less than 20 % water content (of the weight of the fruit). Dates containing more water must be dried (artifi cially or by the sun) to a level of 16 % to 19 %, to make it possible to preserve them without refrigeration. In this state the fruit has its customary appearance (according to each specifi c variety), with its characteristic wrinkles and colour, ranging from dark brown to light yellow.
There are many methods of harvesting, depending on different date growing countries, specifi c regions and local traditions. Some of the fruit is harvested when it is very hard and dr-y – stone dates. These varieties can be harvested at a great height and dropped right down to the ground.
Other varieties require gentler treatment, and the common method used is to cut the fruitstalk and to lower it on a rope with a hook or to use mechanised platforms which take the worker up to the bunch. For these varieties harvesting is also the first stage in the treatment process, so that the fruit reaches consumers in the state required.
5. Other date palm products and by-products.
Here we shall only mention products and by-products made from the fruit itself. Other parts of the palm, such as the trunk, the leaves and the male pollen, are also used in various ways, but will not be discussed in this chapter.
The raw material used for the products usually consists of dates of a lower quality, with a low percentage of sugar, but on no account rotten, sour or fermented dates. Good quality dates may also be used when there is a surplus of fruit on the market.
Most of the dates are sold without seeds, 80 % of Deglet Nour are sold in the USA in this way for consumer convenience. The seeds are removed by hand or by machine, the methods range from seed removal while ensuring the dates remain whole and their texture is not harmed, to the complete grinding of the product. When seed removal is done by machine, some seeds may remain, and a warning must be included on the packed product.
Pitted pressed dates: This is a very useful basic product both in producing and in importing countries (European countries, the USA and South Africa). The dates are pitted by hand or by machine, pressed into a mould and vacuum packed. Packing in this way and with the right amount of moisture (less than 20 %) preserves the stability of the product over time without refrigeration. If these rules are not adhered to, the product may be harmed by microbiological processes or through sugar crystallisation. This product is used mainly as a fi lling for cakes and biscuits, especially during the Muslim Feast of Holy Ramadan (Figure 83).
Date paste: In order to preserve the stability of the products over time and prevent their going bad, specifi c rules must be followed during the date paste production stage. Brix must not be less than 65o and the acidity must not rise above pH 4.5. In this case the paste can remain in its natural state (without the need for preservatives). If the above conditions do not exist, the product must be pasteurised or sterilised. These pastes can be used as fi llings for cakes (with the addition of various fl avours, as required). The great advantage of these pastes is that their melting temperature is higher than that used in baking, so that the fi lling does not run out of the cake during baking.
Date syrup (sometimes called dibs or rub): Five production stages are involved: pretreatment, extraction of juice, clarifi cation, concentration and fi ltration. The rules with regard to brix and sourness must be strictly kept. The syrup is used to sweeten various foods.
Date products resulting from intensive processing: Sauces for steak or chutney: The dates serve as a source of sugar and to form the body of the sauce.
Other types of products are extruded date pieces or diced dates. The dates are pressed through holes of 5 – 12 mm; the product is covered with dextrose or oat fl our in order to prevent the little pieces from sticking to each other.
Alcohol: Alcoholic drinks can be produced by the fermentation of the dates.
6. Packinghouse management and quality standards.
6.1 Packinghouse management.
Modern management focuses on marketing and quality control. The manager is responsible for:
* Contact with marketing and production management according to the requirements of the market;
* The labour force (permanent and temporary), for its training and guidance in fulfi lling the necessary tasks, and for the well-being of the workers;
* The appointment of a team of assistants, and of the managers of the various departments;
* The purchase of raw materials and the administration of the stocks;
* For the whole issue of quality, working for constant improvement (standards, control, follow up);
* Development: long term perspectives of new ways of expanding the plant, its upgrading and the development of new products;
* Storage and shipment on the appropriate scale and according to demand;
* Ensuring funding of ongoing operations and of development, obtaining payments from clients and paying suppliers (especially suppliers of fruit, according to contract type);
* The execution of all safety instructions according to the law, in order to protect the workers;
* Care for the quality of the environment and the investment of the necessary funds (treatment of poisonous gases and of sewage etc.);
* Contact with the relevant Governmental institutions, the Ministry of Agriculture for phyto - sanitary permits and extension services, and other Ministries on the issues of quality and health;
* Ensuring the profi tability of the packinghouse by good management.
6.2 Quality standards.
When dates are produced for export, certifi cation has to take place by an internationally recognized certifying body. Most importantly, it needs to be recognised by the buyer.
Quality standards for dates have been set by different bodies. Earlier in this chapter the Codex Alimentarius was mentioned. The Codex Alimentarius sets permitted levels of residues of pesticides (MRL = minimum residue limit) according to types of material and species of fruits, vegetables and other foodstuffs. The Codex Alimentarius is published by FAO and WHO and has been ratifi ed by most of the 146 member countries.
Furthermore, UN/ECE norms have been set for whole dates. Sorting criteria as well as criteria concerning moisture content are set in these norms, which are accepted in most EC countries, although the exact levels might differ per country.
Quality standards are set per country and per variety. Individual countries set their own standards with regard to quality. This can be seen as an agreement between the buyer and the producer with regard to what the product should look like.
Health regulations are designed to ensure that the produce is safe for human consumption.
Quality systems are complementary to the above technical requirements and those of the customer. They do not replace them. Two quality systems are ISO 9000 and HACCP - Hazardous Analytical Critical Control Point.
“ISO 9000”.This is a quality system, a model for quality, assurance in design, development, production, installation and servicing, designed by the International Institute for Standardization (ISO). The ISO 9000 international standards were accepted as European standards in December 1987. On the one hand, these norms refl ect worldwide agreement in the fi eld of quality assurance, and on the other hand, they are binding for the European Union and the countries of European Free Trade Association.
Key concepts in the framework of the ISO 9000-9004 norms are: Quality management, Quality care, Quality system, Quality control, and Quality assurance.
Certification mostly takes place by checking and supervision, carried out by an independent, impartial and expert certification institution. In most countries, it is possible to obtain detailed information about ISO 9000 and certifying bodies fromN ational Standardization Institutes. Information can also be obtained from ISO, P. O. Box 56, CH-1211 Geneva, Switzerland. (CBI, 1997/2: European regulations manual).
In the usual type of production plants such as packinghouses for dates, the relevant standard is 9002. The standard defi nes the requirements of the quality system. They are mainly intended to prevent lack of coordination at all stages of quality control, from the reception of the fruit from the field (in some cases even before) until it reaches the client and consumer (and deals with complaints, if necessary). Keeping to this standard assures the customer that the quality system of the supplier ensures that the product fulfi lls the stated quality requirements (as defi ned by the client or by the standard).
ISO 9002: 1987 Quality system requirements.
Qualifying for “ISO 9000” has the advantage of providing a common language between supplier and client in matters of quality, ensuring that the product has been officially recognised as such.
Issues of quality will always be the responsibility of top management and will be passed down the hierarchy.
HACCP - Hazard Analysis Critical Control Point.
The Hazard Analysis Critical Control Point (HACCP) is a European standard for the food industry. The EU Directive on Hygiene of Foodstuffs (93/43/EC) stipulates that “foodstuff companies shall identify each aspect of their activities which has a bearing on the safety of foodstuffs and ensure that suitable safety procedures are established, applied, maintained and revised on the basis of an HACCP system” (CBI, 1996). It is a method of analyzing risk factors related to food, the risks for the consumer using the fruit. The food is analyzed linearly throughout the process, and broadly for chemical, physical and microbiological risks. The method makes it possible to detect critical points of risk and fi nd ways of preventing it. The critical points in date processing are:
Chemical risk – in dates the source of risk is from the residue of substances used in pest control in the fi eld. This is a critical point when receiving the fruit at the plant. The solution lies in guidance and supervision in the fi eld, in the use of permitted substances only and in their correct concentration, and by sampling the fruit for testing for such residue.
Another, less signifi cant, chemical risk in the packinghouse is the use of detergents. This risk is prevented by the use of cleaning materials permitted in the food industry and separate locked storage.
Physical risk – various foreign bodies:
metals: the critical point is after final packing; using a metal detector; calibration and ongoing testing must be a regular procedure.
Glass: the following code must be followed:
a) no glass may enter the plant (no glasses, jars etc.)
b) light bulbs must be protected.
c) the windows must be made of unbreakable material.
d) specifi c procedures in case of broken glass.
Microbiological risk – mainly infection, for example, by coliforms and salmonela. Prevention techniques are however available and can be summarised as follow:
1. Rules regarding personal hygiene; workers wash their hands with soap on entering the plant and on leaving the toilet.
2. Washing the fruit with water qualifying as drinking water.
3. Preventing fl ies, mice and birds from entering the area of the plant.
4. The sorting system must be cleaned according to regulations.
5. Ongoing checks of various parts of the plant in order to detect possible pollutants, ensuring that the fruit is clean.
6.3 Packinghouse requirements.
In order to enter the supermarket level in Europe, it is necessary to maintain a minimum standard regarding cultural techniques, harvesting, post-harvest handling, packing, health and hygiene, and quality control systems.
* Must be a separate, defined area which is used only for packing. Storage of cartons must not be carried out in the packinghouse.
* The fabric of the building must be in good condition. Windows when open, must be screened to prevent insect ingress.
* Light level must be adequate for selection and grading.
* There should be adequate facilities for the collection and disposal of waste material at frequent intervals to discourage fl y infestation and the development of latent fungal infection.
* Risk of contamination from local industries should be minimised.
* The packinghouse layout should be designed in such a way as to keep the raw material and the fi nished product separate, and to encourage the smooth fl ow of the product through the selection and packing system.
* The packinghouse and equipment should be cleaned during the day on a “clean as you go” base.
* Work surfaces should be non-porous and easy to clean. Materials such as stainless steel and formica are ideal.
* Containers used during production such as harvesting crates should be easy to clean polythene or other durable plastic. They should be cleaned regularly and stored in areas free from risk of contamination.
* Packing material must be stored in a clean dry area free from risk of contamination.
* All equipment used for quality control such as scales, temperature probes, refractometers, etc. must be regularly checked for accuracy.
The storage of packing material is very important and care should be taken that no insects can enter the material and be exported. Fly/insect catchers should be installed in the packinghouse and a no smoking policy should be implemented in the area where dates are packed.
* It is important that all staff are aware of their responsibilities for the health and.
* Staff suffering from gastric disorders causing sickness must not be allowed to work until completely recovered and cleared of the disorder.
* All cuts, sores and other skin problems must be covered by a blue industrial dressing.
* Hand washing and toilet facilities should be adequate to meet staff requirements. Toilets must be maintained in a clean hygienic condition.
* Wearing of cosmetic jewellery should be discouraged and should be kept to an absolute minimum at all times.
* Protective clothing that adequately covers day-to-day clothes must be worn in the packinghouse at all times.
* Smoking, chewing tobacco and spitting is strictly forbidden in the packinghouse.
* Rest areas, away from production should be provided for food and drink consumption.
* The storage of chemicals, fuel and oil should be in a secure area away from the packinghouse.
The following information should be printed on all packaging material for exports:
* country of origin;
* grown and packed by (address);
* product and variety; e.
* category (class 1 or grade 1).
The aim of setting these packinghouse requirements is to maintain uniformity in products, quality, production standards and liabilities of all packing stations supplying to an umbrella marketing organisation.
The conditions and requirements actually implemented in Israel are:
1. Certification – approved by the authorities as a food packer, e. g. Ministry of Health, FDA or equivalent body.
2. Knowledge of the sorting, selection, grading and packing of dates.
3. Approved fumigation facilities for use of methyl bromide.
4. Approved and licensed operator of methyl bromide fumigation facilities.
5. On site quality control and data recording throughout the whole process.
6. Weighing and measuring standards and set-up of equipment maintained.
7. Long term cold storage rooms to accommodate a range of varieties before and after selection and packaging.
8. Administration and office facilities to meet internal and marketing organisation needs.
9. Equipment and ramp to load sea containers/trucks.
10. Documentation of produce in/out that meets marketing organisation needs.
11. Packing station product quality guarantee to the consumer.
Figure 80. Date harvesting by mechanical ladder (Israel)
Figure 81. Washing of dates.
Figure 82. Sorting of Medjool.
Figure 83. Pitted pressed dates.
Figure 84. Transport of Barhee bunches from the field to the packinghouse.
Figure 85. Packing of Barhee bunches in the 5 kg boxes.
Figure 86. Classifi cation and treatment of Deglet Nour for export (North Africa).
(Source: Barreveld, 1993)
Figure 87. The relationship between moisture % and water activity.
Figure 88. Sun drying of too soft Medjool fruits.
CHAPTER VIII: POLLINATION AND BUNCH MANAGEMENT.
CHAPTER VIII: POLLINATION AND BUNCH MANAGEMENT.
by A. Zaid and P. F. de Wet.
Date Production Support Programme.
Being a dioecious species in character, date palm sexes are borne by separate individuals. The unisexual flowers are pistillate (female) and staminate (male) in character. The male palm produces the pollen and the female palm produces the fruit. The fl ower stalks are produced from the axils of the leaves in similar positions to those in which offshoots are produced. The inflorescence consists of a long stout spathe which, on bursting, exposes many thickly crowded floral branchlets which are stout and short in male, and long and slender in female. One adult female palm, on average, produces 15 – 25 spathes that contains 150 to 200 spikelets each. The male flowers are borne single and are waxy white, while the female flowers are borne in clusters of three and are yellowish green in colour.
Natural pollination by wind, bees and insects is found to yield a fair fruit set in various areas of the date growing countries (Marrakech/Morocco; Elche/Spain; San Ignacio, Baja/Mexico; Ica/Peru, for example). All these regions are characterised by their 100 % seedling composition with about 50 % males. In the absence of such natural pollination, female flowers are not fertilised. This leads to the development of carpels and consequently parthenocarpic fruits without any commercial value are obtained. Date growers in these areas are aware of artifi cial pollination techniques, but because of insufficient economic pressure incentives, such techniques are not applied.
The very old and primitive pollination technique consisted of placing an entire male spathe in the crown of the female palm and leaving the rest to wind pollination. According to Chevalier (1930) and Dowson (1961), this technique was used in Mauritania and Libya, respectively. It has been abandoned because it could not yield uniformly good fruit sets and requires the availability of large number of male spathes (Dowson, 1982).
Commercial date production necessitates artificial pollination which ensures good fertilisation and overcomes disadvantages of dichogamy and also reduces the number of male palms. The male/female ratio in a modern plantation is 1/50 (2 %). Artificial pollination could be realised according to a traditional method or by using a mechanised device (Enaimi and Jafar, 1980).
1. Pollination techniques.
Depending on the type of pollen available, one of the following three techniques is used:
1.1 Fresh male strands.
The most common technique of pollination is to cut the strands of male flowers from a freshly opened male spathe and place two to three of these strands, lengthwise and in an inverted position, between the strands of the female infl orescence. This should be done after some pollen has been shaken over the female inflorescence (Dowson, 1982) (Figure 64). In order to keep the male strands in place and also to avoid the entanglement of the female cluster’s strands during their rapid growth, it is recommended to use a twine (a strip torn from a palm leafl et or a string) to tie the pollinated female cluster 5 to 7 cm from the outer end.
1.2 Pollen suspension.
Laboratory and fi eld experiments on three varieties from Saudi Arabia (Khalas, Ruzaiz and Shishi) have shown that a pollen grain suspension, containing 10 % sucrose and 20 ppm GA3 could be used for pollination (Ahmed and Jahjah, 1985). Pollination sprays were found to be as good as hand pollination in relation to fruit setting. Similar results were also obtained by Ahmed and Al-shawaan (1983) who tried pollen grains suspended in 10 % sucrose solution. Fruit set was 80 % using this suspension technique while only 60 % was obtained when using the classical hand pollination technique. On the other hand, a suspension solution containing pollen grains, sucrose, boron, glycerine and GA3 did not match the results of hand pollination (Hussain et al., 1984).
1.3 Dried pollen.
This pollination technique is more economical and allows proper use of the pollen as well as adequate control of the timing of pollination. Dried pollen could originate from the last season, from early maturing males of the same season, or from few days old male flowers. There are several techniques to apply dry pollen:
(a) Cotton pieces: The most common technique of using dry pollen is to dust it on cotton pieces about the size of a walnut and place one or two pieces between the strands of female inflorescences.
(b) Use of a puffer: A small manual insecticide duster, known as a ‘puffer’ is also used to apply dry pollen. This technique is used either alone or in addition to the cotton pieces technique (Nixon, 1966).
(c) Mechanical pollination: Mechanical pollination was developed mostly in the New World of date palm (USA and Israel) where labour is expensive and not always available. It consists of pollinating freshly opened female spathes from the ground with the use of a special apparatus. Mechanical pollination has been one of the most important alternatives when the labour has been reduced by 50 – 70 % (Nixon and Carpenter, 1978; Ghaleb et al., 1987). It is estimated that a man must climb a date palm eight to ten times from the time of pollination through to crop harvesting. According to Perkins and Burkner (1973) all other cultural operations for a 25 ha plantation could be completed with a labour force of approximately 200 men, whereas pollination requires nearly 700 men-days during the peak period. Mechanical pollination from ground level for three times and with 1:4 (pollen/fi ller ratio) was recommended by Nixon and Carpenter (1978) to achieve high yielding of most date varieties. It seems that the frequency of mechanical pollination as well as the suitable concentration of pollen/fi ller ratio are the most important factors in date palm pollination.
According to Perkins and Burkner (1973), a ground-level duster is capable of pollinating 24 to 32 ha per season. In order to accommodate the palm height and also to direct the pollen delivery tube near the bloom area of each palm, the machine is equipped with a variable height platform capable of 4.5 m vertical movement. The duster is driven along one side of the date row and then returns on the opposite side to fi nish the pollination cycle. Such mechanical pollination will require two labourers and could be realised according to two approaches:
(i) Pollination of each freshly opened female spathe or;
(ii) Spraying of the whole female leaf canopy just above the opened spathes.
The first approach is the more accurate one, but requires the farmer to have good knowledge of his plantation as well as good record - keeping to ensure the pollination of all spathes. The second technique is economically feasible and saves time. However, a high rate of aborted fruits could occur when this technique is used.
During early season pollination, or when the pollination season is characterised by low normal temperatures, it is recommended to alternate pollination of sides of the palm at 4 to 7- day intervals. This overlapping of pollination was shown to yield more reliable results than full palm pollination at one time (Nixon and Carpenter, 1978).
There is a trend to use a simple mechanical device called hand pollinator. It is made of a rubber “bulb”, a plastic bottle containing pollen, 5 to 8 m plastic tube attached to a solid aluminium tube (Figures 65 and 66). By repeatedly pressing the “bulb”, pollen located in the bottle is expulsed with the produced air and moves through a plastic tube towards the female spathes. Fruit set resulting from the use of mechanical pollination is usually poorer than that following hand pollination, but fruit quality and yields are found to be equal as a result of decreased thinning of the mechanically pollinated inflorescences. Furthermore, it is worth mentioning that mechanical pollination requires approximately 2 or 3 times more pollen than manual pollination. To overcome this problem, date growers are mixing the pollen with adjuvants, also called fillers, such as talc, bleached wheat flour, walnut-hull dust with a ratio of pollen/filler 1:9 or 1:10. One gram of pollen could then pollinate ten female spathes. Adjuvants must present the following characteristics: their particle size must be similar to the pollen grain with no harmful effect on the pollen’s viability, or its germination on female stigmates. Hamood and Mawlood (1986) found that repeating mechanical pollination, 4 times during the season by using 1:10 (pollen/fi ller ratio), increased the total yield of Zahdi cultivar.
The advantages of mechanical pollination could be summarised as follows:
* reduction of labour and duration of pollination, both contributing to the reduction of the cost of pollination. Furthermore, it does not require a highly trained labour as with the traditional technique;
* ensuring the possibility of pollinating a palm at several times in a short period of time;
* Allowing the use of a mixture of pollen originating from different sources, thus ensuring good fertilisation;
* eliminating the risk of accidents occurring as with the old method of climbing a palm several meters high.
(d) Aircraft pollination: Experiments with pollinating of dates with an aircraft were conducted in the Coachella Valley of California on Deglet Nour variety by Brown and Perkins (1972). Results showed that even though temperatures and weather conditions were favourable, both the helicopter and fi xed-wing methods of application yielded less fruit sets than the hand pollination method. This technique was abandoned as it required at least 4 to 5 times the amount of pollen traditionally used, and was also found to be not economically feasible.
2. Pollen harvest and handling.
A male spathe that is ready to split assumes a brown colour and a soft texture. Immediately after the spathe breaks, the male inflorescence reaches its maturity and male flower clusters must be cut at this stage. To prevent wind or bees from causing loss of pollen it is recommended that the freshly-opened spathe be cut early in the morning.
Date growers traditionally harvest the male spathes one or two days after their opening and place them in a shaded and moisture-free area for drying (Figure 67). Strands are then detached and stored till needed for the pollination of female inflorescences. Transport of strands for a long distance (between two date plantations) must be handled with maximum care. The use of paperbags is recommended to preserve the pollen and avoid losses.
The common practice of cutting the male spathe a day or two before its natural opening as practised in the Old World (Middle East and North Africa) is not recommended because it requires a high level of experience and familiarity with the male palms (Nixon and Carpenter, 1978). The technique is to press the middle or lower part of the male spathe between the thumb and forefinger. If a crackling noise is heard, it is a sign of maturity of flowers. In such a case the spathe could be cut and flowers taken to the storage room for drying.
A pollen-handling protocol necessitates the rapid and effi cient dehydration of moist pollen before its storage.
High temperatures have a negative effect on pollen drying and storing processes. Pollen exposed to direct sunlight or placed near a source of heat, will rapidly deteriorate and lose viability (also called vitality) Viability is defi ned as the ability of a pollen grain to germinate and develop (Gerard, 1932).
3. Extracting, drying and storing pollen.
The emergence of many early inflorescences on female date palms before the opening of an adequate number of male spathes on available male palms always results in scarcity of pollen. Furthermore, it is well known that, depending on climatic conditions, a date grower could face a season where a heavy early female bloom develops. Consequently, the storage of pollen within the pollination season (2 to 3 months) or from one season to another is a necessity, mainly for pollen known to have a high metaxenia effect. Date growers should plant enough males, select the best ones and propagate them in order to meet their own needs without relying upon other sources for pollen.
Freshly opened male flowers contain a high level of moisture; consequently if they are not to be used immediately, their prompt drying is important in order to avoid the destruction of pollen by moulds. As mentioned above, air movement and sunlight are to be avoided in order to protect pollen viability. There are various ways and techniques to store the pollen depending on the quantity to be stored, storage conditions and the duration of storage.
& # 8211; Storage of strands.
It is a simple way to store a small quantity of pollen; strands are separated and spread in a thin layer on paper in a shallow tray in a shaded/protected area.
& # 8211; Male fl ower clusters.
Clusters are put on top of screen-wire trays or shelves with a container beneath to catch the dry pollen that falls from the fl owers; Note that the pollen quality remains unchanged even though the flowers turn dark within 3 to 7 days. This storage technique is mostly used for handling larger quantities of pollen.
Date growers in Iraq (Dowson, 1921) and in Egypt (Brown and Bahgat, 1938) conserve the pollen by placing the flowers, usually dried and crushed, in a muslin bag and left in a well dried-ventilated area.
& # 8211; Mechanical pollen extractor and collector.
The machine is made of a vertical shaker, a collection barrel, a cylindrical screen tumbler, a rotating screen disk, a cyclone separator and a suction fan (Figure 68). The machine can daily handle up to 450 male fl ower clusters and collects approximately 40 % more pollen than any other extraction method. The pollen viability and longevity were found to be unaffected by such mechanical extraction.
Moderate temperatures in a dry room will be satisfactory enough to store pollen for 2 to 3 months consequently covering the needs during the pollination season. Pollen storage from one year to the next requires more controlled conditions and an adequate drying system. Once the pollen is well dried and cold stored in an airtight container, it could be safely re-used during the next season with very little loss of viability. Nebel (1939) found that a relative humidity of 50 per cent and a temperature of 2 to 8°C were the optimum conditions in deciduous trees for storage of pollen for more than four years.
Aldrich and Crawford (1941) emphasised the importance of keeping the pollen as dry as possible during the storage period. To maintain zero per cent humidity, dry pollen is placed in an open jar within a larger airtight container (a dessicator) in the bottom of which are well dried lumps of calcium chloride (Ca Cl2) as a dehydrating agent (Figure 69). Other absorbents that can also be used are saturated solutions of zinc chloride (ZnCl2), calcium nitrate (N(CaO)³)²-4H²O) and potassium chloride (KC1).
Dessicators must then be maintained at low temperatures in a refrigerator (between 4°C to 7°C) (Aldrich and Crawford, 1941; Oppenheimer and Reuveni, 1967). According to the same authors, approximately 500 g of calcium chloride is enough for 2 – 3 kg of pollen.
According to Hamood and Bhalash (1987), in order to obtain good fruit set it is recommended that the stored pollen first be tested for its viability; once proven the pollen should be mixed with a filler (e. g. wheat flower; industrialised-non perfumed talc; etc.) at a rate of 1/9 respectively; the mixture must be prepared immediately before pollination. It is also a good practice to mix the fresh pollen with that stored for one year.
Cold storage using a common refrigerator (4° to 5°C) or a freezer (-4 to – 18°C) was proven to be satisfactory (Figures 70 and 71). According to Nixon and Carpenter (1978), lower temperatures under conditions subject to less fluctuation are safer. As mentioned earlier, the evaluation of the viability of the pollen, either fresh or stored, is important before the pollination operation. The use of selected pollen with a high degree of viability will ensure a better fruit set and consequently an acceptable yield. Pollen could be dried by lyophilisation using freezing temperatures between -60 and -80°C. Water is eliminated by sublimation between 50 and 250 mm Hg (Djerbi, 1994).
It was also found that pollen from the date palm could be cryogenically stored successfully using liquid Nitrogen (-196°C) (Tisserat et al., 1985). The longest period that palm pollen was treated with liquid nitrogen, was 435 days (Tisserat et al., 1983). These results suggest that long-term storage of pollen from the date palm, using ultra-low temperatures, can be used with no deteriorating effect on pollen viability and on fruit set. Recently, Kristina and Towill (1993) placed date pollen over a saturated salt solution with a lower relative humidity (CuSO4 – 5H2O) for approximately 2 hours; the moisture content was reduced to less that 15 %, and the amount of freezable water in the date pollen dropped to 5 % making storage in liquid nitrogen feasible (Table 59).
Germination values for fresh, dry and liquid nitrogen stored pollens.
Source: Kristina and Towill, 1993.
¹ Time in liquid nitrogen storage for these samples ranges from 24 h (maize) to six months.
² Cattail and pecan pollens were dry when collected: fresh and dry percent germination values are synonymous.
4. Pollination effi ciency.
Pollination of 60 – 80 % of the female flowers is considered satisfactory and will usually lead to a good fruit set. The pollination efficiency is affected by several factors and consequently fruit set is highly dependent on these factors. The pollination time, fl owering period of male palm, the type of pollen, its viability and amount, and the female flowers receptivity are the main factors to take into account.
Satisfying pollination results are obtained within 2 or 4 days after the female spathe has opened. March and April is the normal pollination period in the Northern Hemisphere; July and August for the Southern Hemisphere. Variety and season could delay or advance the opening of the flowers.
Flowering period of male palm.
Flowering periods of male and female palms should be synchronised in order to have enough pollen when the female spathes open. It is preferable if the male spathe opens 2 to 4 days earlier than the female spathe. Hence, male palms should receive the same cultural techniques as the female palms and must preferably be planted in areas that receive more sunlight; (i. e. in the northern hemisphere, their exposure to the south favours, in general, early fl owering). Lack of irrigation during fall and winter at the northern Negev (Israel) was found to be the only reason of delaying the fl owering date, and consequently resulting in low fruit set (Oppenheimer and Reuveni, 1965).
Pollen source and quantity.
Studies conducted by Nasr et al. (1986) revealed that seedling males are highly variable in their growth vigour, spathe characteristics and pollen quality. Also, the amount of pollen grains produced by spathe varied greatly from one male to another (0.02 – 82.29 g/spathe). The size of the pollen grain was also found to vary among males (Asif et al., 1987); Mean diameter of pollen varied from 16 to 30 microns.
It is well known that different varieties of date palm require different amounts of pollen (Dowson, 1982). Using fresh male strands, the number required for pollinating a female spathe may vary from 1 to 10 depending on variety. Furthermore, some varieties have larger female inflorescences than others, which require more male strands.
The results of a research experiment conducted at the USDA Citrus and Date Station (Indio, California-USA) have however shown that all except 3 or 4 of more than 100 varieties of dates have been pollinated uniformly with satisfactory results by using only 2 to 3 male strands per female inflorescence (Nixon and Carpenter, 1978). Applying more strands (when pollen is not scarce) is considered as good insurance and will have no disadvantages.
Most of the male date palms used throughout the world’s date growing areas are of seedling-origin with a great variation regarding pollen quality. However, and thanks to the selection programme conducted in various countries, several male palms were selected and are actually beginning to be recognised as varieties (Mosque, Mejhool BC3, Deglet Nour BC4, Fard No. 4, Jarvis No. 1, Boyer No. 11 (USA); Deglet Nour, Hayani and Bentamouda (Egypt and Sudan). There is however, still room for improvement and a date grower should take into consideration the following desired characters before selecting and using any male palm:
* Clusters of the male flowers.
The size and number of produced inflorescences per male palm are the first criteria to look for. Indeed, the more and larger the male inflorescences available, the fewer palms per ha will be required. As mentioned earlier, the average pollen bearing capacity of a good male palm should be suffi cient for 50 female palms. The abundance of pollen is determined by both the number of flowers and the pollen quantity per fl ower.
According to Monciera (1950) and to Wertheimer (1954), good male palms from Algeria annually produced an average of 740 g of pollen with a maximum of 2,133 g. However, both the number of inflorescences and the weight of pollen of these palms showed an alternancy phenomenon between high and low yielding years. According to Djerbi (1994), a good male palm should produce an average of 500 g of pollen with a regular production over time. Large quantities of pollen do not however, guarantee the quality of pollen produced and consequently its effect on the fruit (Metaxenia).
In regions where inflorescence rot occurs (caused principally by the fungus Mauginiella scaettae cav.), pollen should be taken only from healthy male palms. Evidence suggests that contaminated pollen may spread the fungal spores and establish the disease in female palms.
It is well known that the pollen not only affects the size of the fruit and seed (affected more by fruit thinning) but also the time of ripening (Swingle, 1928). Metaxenia is not to be confused with Xenia, which is the effect of the pollen on the endosperm (embryo and albumen). Metaxenia effect was verifi ed by several investigations in the USA (Nixon and Carpenter, 1978), in Israel (Comelly, 1960), in Pakistan (Ahmad and Ali, 1960) and in Morocco (Pereau-leRoy, 1958). The effect of pollen on the time of fruit ripening was proven to be beneficial and is actually considered as the most important practical application of metaxenia. Producing and selling date fruits at high prices early in the season, along with the aim of having more uniform and short ripening period (avoiding a prolonged harvest) are the two main objectives of using a selected pollen of high metaxenia effect. A third useful application of metaxenia is where the development period of the plant is characterised by an insuffi cient sum total of heat for the fruit ripening of late varieties.
It is worth mentioning that metaxenia effect could also be successfully used to speed up the fruit maturity and consequently escape the rain damage that is usually expected at the end of the fruit development period (Algeria, Tunisia, USA, etc.); The use of the Fard 4 male has advanced the maturation stages of various varieties all around the world by two weeks. However, under a summer-rain season, (India, Pakistan, Namibia, Republic of South Africa, for example) late ripening could be more desirable and the selection of males with late ripening effect is recommended.
Usually, a male seedling of a specifi c variety will set better fruits with specifi c female varieties. Djerbi (1994) observed that some date varieties will have a better yield if they are pollinated with some males rather than with others. However, several authors (Monciero, 1954; Pereau-leRoy, 1958) did not observe any interclonal incompatibility, and fruit sets obtained were always satisfactory. Pollen of 75 different Tunisian date males with more than 10 female varieties were examined so as to select those that have advanced maturity and improved date quality (Bouabidi and Rouissi, 1995). Six types of pollen were proven to be earliness-inducing (DG9, DG4, DF4-1, HF4-1, HF4-3 and HF4-5). Such a character depends on the female variety with no relationship between time of maturity and date fruit quality. These results confi rm the fi ndings of Bouguediri and Bounaga (1987).
As a first conclusion, a test to verify if the pollen of the potential male is satisfactory for the varieties on which it will be used, is important before looking into other characteristics.
The capacity of pollen to germinate and grow normally is known as viability. The assessment of viability of freshly collected as well as stored pollen is often desirable before using them for pollination. The pollen from genetically different male palms have varying viability. Therefore, a viability test can help in selecting the pollen types which are highly viable. The use of highly viable pollen is likely to result in more fruit set and higher yield.
Applying enough pollen does not guarantee a good fruit set unless the pollen used is viable with a high germination percentage. As mentioned earlier, the evaluation of pollen’s viability, whether fresh or stored, is essential before the pollination operation. The use of selected pollen with a high degree of viability will ensure a better fruit set and consequently an acceptable yield. Because of their seedling-origin, different male palms will produce different pollen from the quality point of view (cf. Metaxenia) and also different percentages of viable pollen.
Pollen from both the earliest and the latest male inflorescences was found inferior to that of others on the same palm (Monciero, 1954). The low fruit set resulting from the use of either the earliest or the latest male inflorescences could be explained by the non-maturity of their pollen, usually caused by low summation of heat.
Environmental conditions such as high temperature, low humidity, salinity build up and UV radiation may infl uence pollen viability.
5. Germination test of pollen grains.
In vitro germination allows the measurement of the pollen intrinsic aptitudes to germinate outside any interaction between pollen and stigma. Furthermore, pollen capacity to fertilise the ovule and set the fruit is considered as an estimation of natural intrinsic aptitudes. Hence, in vitro germination is considered as the most valuable test of pollen viability (Boughediri and Bounaga, 1987). There are several rapid and reliable techniques that ensure excellent and fast germination, normal pollen tube growth and almost no bursting of pollen grains.
Albert’s germination technique (1930)
A small amount of pollen grains is dusted on a drop of 20 % sucrose placed on a cover glass, which is then inverted over a glass cell. A thin fi lm of vaseline is placed on the top of the cell to seal the cover glass to it. It is then placed in an incubator at 27°C for 12 to 14 hours and inspection is done under a microscope. An initiation of a pollen tube growth is considered as evidence of germination. Germination counts must be taken from 4 fields for each slide.
Monciero’s germination technique (1954)
The medium is a solid and consists of 1 % of agar and 2 to 10 % of glucose; It is executed at an average temperature of 27°C during 24 hours.
Brewbaker and Kwack’s medium (1963)
It is a liquid medium developed in 1963 but modifi ed later by Furr and Enriquez (1966):. 15 % sucrose, 0.5 g of boric acid (H3BO3), 0.3g of calcium chloride (Ca(NO3)2. 4H20), 0.2 g of magnesium sulphate (MgSO4) and 0.1 g of potassium nitrate (KNO3), are added to 1 litre of distilled water. Ten mg of pollen grains is then added to 50 ml of medium and put in 125 ml Erlen fl ask and dark incubated at 24 to 32°C. This latter temperature was found to be the optimum.
The best percentages of in vitro germination of date pollen of various Algerian cultivars were obtained with 15 % of sucrose and 0.1 % of boron at 27°C in the dark (Boughediri and Bounaga, 1987). Maximum pollen germination was also observed at 0.05 ppm succinic acid and 0.5 ppm fumaric acid in a basic sucrose (20 %) and agar (1 %) medium (Asif et al., 1983).
Tisserat et al. procedure (1983)
Pollen grains are germinated in a liquid medium consisting of 500 mg. l -1 H3BO3, 300 mg. l -1 Ca(NO3)2.4H2O, 200 mg. l -1 MgSO4. H2O, 100 mg. l -1 ethylenediamine tertra acetic acid and 200 g. l -1 sucrose. Ten milligrams of pollen grains is to be added to 250 ml Erlenmyer fl ask containing 5 ml of the germination medium. The fl asks are capped with sterilised cotton plugs and incubated at 27 – 28°C for 24 hours under dark conditions. Two drops of germination liquid medium from each treatment are separately spread on a slide and examined under a light microscope to obtain the germination percentage. Four random replicates are to be used and only 100 pollen grains could be examined in each replicate. The emergence of pollen tube growth is considered as an indicator of pollen germination.
The best medium from all the above for date pollen germination is the modifi ed Brewbaker and Kwak’s medium.
Staining technique of Moreira and Gurgel (1941)
Take a small amount of the pollen grains and place them on a slide with 1 – 2 drops of 1 % acetocarmine solution. The slides are then heated for a few minutes on a hot plate. Examination is conducted under a microscope at 200 × magnifi cation power to assess the viability of the pollen grains (use 4 fi elds for each slide). Pollen grains stained red are considered viable, whereas, the colourless pollen grains are considered non-viable.
Al-Tahir and Asif (1982) determined the effectiveness and reliability of fi ve staining agents as indicators of viability of date pollen. A correlation coeffi cient between pollen staining percentage and germination percentage for 3 (4-5-dimethyl-thiazolyl-2) 2,5 – diphenyl tetrazolium bromide was positive and signifi cant. A similar technique was developed by Alexander (1969) who was able to differentiate between viable pollen grains which turn dark red and non - viable ones which become green. The above staining techniques are based on the colouring of pollen resulting from the fixation of some chemical products on a specific cell’s components; Cytoplasmic and enzymatic colouring agents are the two existing staining products. Within the enzymatic ones we can fi nd 2,3,5 triphenyl-tetrazolium chlorid (TTC) and 3 (4-(dimethyl-thiazolyl 1,2) 2,5 diphenyl tetiazolium bromide (MMT), both at a concentration between 0.1 and 0.7 %. These staining techniques, even though they are easy and rapid, are not recommended because they are not precise enough when compared to the germination test.
6. Female flowers’ receptivity.
Before discussing the receptivity of female fl owers, it is worth mentioning that the female fl owering period is variety and temperature related and does not exceed 30 days (El Bekr, 1972). According to Munier (1973), this period is between 30 to 50 days and could even be longer when the daily average temperature is low. In the northern hemisphere, it is located during February, March and April, while in the southern hemisphere it is from July till early October.
The length of the receptivity period of the pistillate flowers could, in general, vary up to 8 or 10 days depending on the variety (Albert, 1930; Pereau - le Roy, 1958). According to Djerbi (1994), the receptivity period for North African cultivars varies from one variety to another (30 days for Bousthami Noire, 7 for Deglet Nour, 8 days for Jihel and Ghars and only 3 days for Mejhool, Boufeggous and Iklane). Beyond these limits, the percentage of parthenocarpic fruits is higher than 40 %. In Iraq, receptivity of “Ashrasi” variety was found to be optimum before the natural opening of the female spathe, while another variety (Barban) until approximately 20 days after the spathe’s opening (Dowson, 1982).
Al-Heaty (1975) found that the stigmas of Zahidi variety have a receptivity period for 10 days. Oppenheimer and Reuveni (1965), in work conducted on the varieties Khadrawy, Zahidi and Deglet Nour, found that fruit set declined signifi cantly when pollination was delayed 10 days or more after the spathe cracked.
According to Ream and Furr (1969), female flowers of the Deglet Nour variety do not become receptive for possibly 7 days or more after the spathe cracks. Further delay to 13 days caused moderate reduction in fruit set and delays exceeding 13 days greatly reduced fruit set.
Within the pollination period, during which the percent fruit set obtained does not differ statistically, there was a day on which maximal fruit set was obtained: in Khadrawi, on the day of spathe crack; in Zahidi, on the day after and in Deglet Nour, on the seventh day after spathe crack (Reuveni, 1970). Another interesting fact, especially noted with Deglet Nour, is that the day of optimum receptivity varies in different inflorescences of the same date palm.
As mentioned earlier, satisfying pollination results are usually obtained within 2 to 4 days after the female spathe has opened followed by a second pollination passage 3 to 4 days later (Table 60). Furthermore, and as a conclusion, it is well confi rmed that the longer pollination is delayed after the opening of the spathe the poorer the fruit, set and if more than a week lapses the yield is usually greatly reduced.
Length of the receptivity period of various date varieties.
7.1 Effect of temperature.
High temperatures inhibit the development of spathes resulting in a delay of the pollination season. Low temperatures, usually early in the season, also have a negative effect on the fruit set. However, if female flowers open early in the season and their pollination is essential, then the sets could be improved by placing paper bags over the female inflorescence at the time of pollination. Bagging of fl ower clusters early in the season could be practised as an insurance against poor fruit sets caused by cold weather. Bags must be fastened in order to prevent the wind from blowing them off. Such bags must be removed two to three weeks later.
Bagging female spadices using paper bags (40-70 cm) immediately after pollination and during the first four weeks was found to result in a signifi cant increase in fruit set, yield and fruit dimensions of Hallawy cv. (Galib et al., 1988). Furthermore, growth of the pollinated carpels in the bagging treatment was faster that with the unbagged one.
According to Reuveni et al. (1986), improved fruit set obtained on bagged inflorescences might not always be attributable to improved temperature conditions; it probably delays drying of the styles and permits the normal progress of the pollen tube into the ovule even at relatively low temperatures.
Efficient pollination is localised within the period when pollen could fertilise the ovules. It depends on the ovule longevity as well as on the growth speed of the pollen tube, which is highly susceptible to low temperatures. During the pollination season, it is recommended not to pollinate in the early morning or late afternoon, because of the negative effect of low temperatures on the fruit sets. Ten to 15 % higher fruit set was experimentally obtained when pollination was conducted between 10:00 a. m. and 03:00 p. m. (Surcouf, 1922; Pereau-Le Roy, 1958). Laboratory results have concluded that an average temperature of about 35°C is optimum for pollen germination; lower temperatures decreased the germination percentage (Reuther and Crawford, 1946).
At locations where daily maximum temperatures during pollination are frequently less than 24°C, mechanical pollination method is not recommended. (Brown et al., 1969).
7.2 Effect of rain.
There is controversy concerning the effect of rain on fruit set. Some consider rain that occurs just after pollination as a washing agent that takes away most of the applied pollen before it plays its role. In such a case, it is necessary to repeat pollination after the rain has ended. Other people consider the negative effect of rain on fruit set as an indirect effect via low temperatures that accompany or follow rain. If temperatures are between 25 and 28°C, most of the pollen tubes reach the base of the style of Hayani variety flowers within 6 hours (Reuveni, 1986); while at 15°C, pollen tubes do not reach the base of the style even after 8 hours. A third explanation of the effect of rain is the reduction of the pistillate fl owers’ receptivity by contact with water. Rain is also responsible for increasing the relative air humidity which favours attacks by cryptogamic diseases that result in the rotting of infl orescences. This high relative humidity is also associated with reducing the pollen’s blow out.
In conclusion, date growers must assume that rain can cause all the above effects, and any pollination operation immediately followed by rain must be repeated in time. Following pollination experiments conducted at the USDA research station at Indio, California (Dowson, 1982) and also according to Pereau-leRoy (1958) there is a limited period (4 to 6 hours either before or after pollination) during which, if rain occurs, pollination and fruit sets are affected and the pollination operation must then be repeated.
7.3 Effect of wind.
In most date growing areas the latter part of the pollination season is usually characterised by severe hot and dry wind which dries out the stigmas of the female fl owers. Cold winds disturb the pollen germination. It seems, therefore, that dry wind storms lead to a faster drying of the styles before the pollen tube reaches the ovule. (Reuveni et al.,1986). Wind velocity could also have an effect on the pollination effi ciency; light wind is beneficial and favour pollination while high speed winds will take away a great deal of the pollen, especially for palms found at the edges of the plantation. In some cases severe wind could also break the infl orescence’s fruit stalk (rachis), blocking the movement of sieve nutrients and fi nally causing the death of the bunch.
Dust storms which leave dust deposits on the flowers during the pollinating season in the southern parts of Israel, and in California are sometimes considered to be the cause of poor fruit set.
II. Fruit thinning.
Fruit thinning is commonly practised in most date growing regions of the world in order to benefi t from the following improvements:
uma. Avoiding the alternancy phenomenon and ensuring adequate fl owering for the next season. Thinning will allow the palm to produce regularly each year rather than to be weakened during one or two years by a heavy production and causing it to produce small and skinny fruits in the next year;
b. Improving the fruit size and consequently satisfying market preference;
c. Improving the fruit quality and texture which will refl ect on the price;
d. Ensuring an early ripening and be first on the market;
e. Early thinning will allow room for the development of the fruit; and there will be less loss of nutrients (N, P,K.) that have to be replaced by fertilisation.. Most sources are hence recommending earlier thinning rather than late thinning.
f. Reducing the weight and compactness of the fruit bunches which will benefi t the harvesting and packing operations.
Date fruit thinning may be realised at three levels:
(i) reducing the number of bunches per palm (removal of whole bunches);
(ii) reducing the number of strands per bunch (mostly from the central part of the bunch); e.
(iii) reducing the number of fruits per strand (bunch thinning; removal of a proportion from each bunch).
1. Bunch thinning.
Bunch thinning that is based mainly on the cutting back of strands will have a maximum effect on the size of fruits if applied at the time of pollination (Nixon and Carpenter, 1978). Cutting out centre strands must wait until the cluster has emerged further. However, and generally speaking for most varieties, it is recommended to wait 6 or 8 weeks after pollination in order to apply the adequate thinning method.
The operation of bunch thinning of the Deglet Nour variety is highly related to the climate and helps reduce damage due to humidity by a greater air circulation around the fruits. This ventilation will reduce the risk of later fruit fermentation, rot and souring. However, with some varieties, the reduction of fruits per bunch may increase the susceptibility of fruit to checking (cracking of the fruit skin; minute cracks in the cuticle and epidermal cells) or blacknose (darkening and shrivelling of the tip). In other climates and with other varieties, Al Bakir and Al Azzauni (1965) found no pronounced effect of thinning on the fruit size.
The objective of bunch thinning is to obtain more uniform bunch sizes depending on the fruit set (removal of fl ower strands if the set is poor and vice versa). Date growers are advised to take into consideration the variety, the relative importance of size and local weather conditions before selecting the thinning method and its degree. Furthermore, the growers should also keep in mind that:
(i) an overthinning will increase puffi ness and blistering (separation of skin and fl esh);
(ii) the earlier thinning is practised, the more effective it is in increasing size;
(iii) large bunches combined with damp weather, will result in fruit rot and souring;
(iv) whatever technique is adapted, all bunches should be thinned uniformly in order to obtain uniform size and quality.
By keeping accurate records, a date grower can soon ascertain the optimum production potential of his palms. Individual palm records would be most useful in working out an effective policy for thinning. Records of the number of fl ower clusters formed annually, will assist to ascertain whether the grower is thinning out too lightly or too severely.
When cutting back the tips and in thinning out the strands, the removal of a total of about 50 to 60 percent of the flowers or fruits on the bunch has been found highly desirable. To justify the expense and work involved in thinning bunches, culture and insect control must be adequate to ensure a harvest of sound fruit.
According to Nixon (1966), fruit thinning in the bunches of Deglet Nour and other long - strand varieties is practised differently, depending on the nature of the bunches of the variety.
Long - strand varieties (e. g.. Deglet Nour)
& # 8211; Removal of the lower one third or slightly more of the bunch by cutting back tips of all strands (Figure 72). The total number of flowers on a strand of average length must be counted in order to determine the desired number to remove and consequently its equivalent by strand’s length.
& # 8211; Removal of entire central strands in order to reduce the number of strands in the bunch by one third to about one half on very large bunches (Figure 72). The total number of strands should be counted to determine how many are to be cut from the centre. Whole outside strands should never be removed because the fruit stalk may die.
With other varieties, the technique is commonly modifi ed with respect to the fi nal amount of dates per strand (20 to 35) and the number of strands per bunch (30 to 50). An average of 7 to 11 kg of ripe fruit per bunch will be obtained depending on the original size of the bunch before thinning, the percentage of fruit set and the amount of thinning.
From experiments conducted by El-Fawal (1972) on an Egyptian variety “Samany”, it would be suggested that the best results may be obtained from a thinning treatment in which about 40 % of the fruit is removed in two step: the first is to cut back, at the time of pollination, the tips of strands suffi ciently to remove about 20 % of the total number of flowers. The second step is to remove about 20 % of the total number of strands from the centre approximately 8 weeks after pollination.
Results from Khairi and Ibrahim’s work (1983) on fruit thinning of Khastawi variety (Iraq) concluded that cutting back tips of strands to reduce the initial fruit load by about 30 % at the time of pollination, and removing weak bunches with low fruit load at the time of bunch bending six weeks later, is useful bunch management to produce high fruit quality.
According to Glasner (personal communication), the thinning of Barhee variety is handled in Israel as follows: At the opening of the spathe, the top 1/3 is cut and 3 to 4 weeks later the grower will come back to thin another 1/3 from the inside. This technique leaves 45 to 50 spikelets per bunch, and 20 to 25 fruits per spikelet.
In general, bunch thinning concerns not less than one-half and not more than three-quarters of the total number of fruits. For most varieties it is generally desirable to reduce both the number of strands per bunch and the number of fruits per strand. However, any method of reducing the number of fruits per bunch will increase the size and weight, and to a certain extent (5 to 10 %) improve the quality; Furthermore, there is no positive correlation between fruit and seed weights amongst all thinning experiments indicating that increase in weight is due to increase in the weight of pulp, but heavy thinning will increase the susceptibility to checking which will reduce grade.
Short strands varieties (e. g. Hallaway and Khadrawy)
These varieties have shorter but more numerous strands than Deglet Nour. Consequently, their thinning must focus on the removal of entire central strands and less should be cut from the tips of the strands. The removal of one-tenth to one sixth of the strands’ tips along with cutting out entirely about one-half of the total number of strands from the centre of the bunch, has given very satisfactory results. According to Russel (1931), the number of strands in Hallaway and Khadrawy varieties should be restricted to 40 to 60 out of 80 to 100 strands by removing the inner ones, and the length of strands should be 35 to 45 cm long by cutting out the ends 7-10 cm. Each strand will then carry 20 fruits (800 – 1200 fruits on each bunch).
Extra large and fancy date varieties (eg.. Medjool)
The Medjool variety, because of its high fruit quality, is the only variety commonly thinned by removal of individual fruits by hand. Instead of cutting back strands, only a certain proportion of fruit is removed from the strands. The fruits of Medjool are so large at maturity that, with a normal set of fruit many fruits are too crowded to be picked without damage and fruits are often misformed by pressure from adjacent fruit born on the same strand. According to Glasner (personal communication), satisfactory results are obtained in Israel by thinning Medjool to approximately 30 spikelets per bunch. 3 to 4 weeks after pollination, the spikelets are thinned by hand, leaving only 10 fruits per spikelet. At the time of harvest, 300 fruits are obtained per bunch with an average weight of 20 g per fruit. An adult palm bearing 10 to 12 bunches, will hence yield 60 to 72 kg of high quality Medjool dates.
2. Bunch removal.
A regular practice is the removal of entire bunches when their number per palm is too high. An adult date palm could produce 20 or more fruit bunches. In fact, if the number of fruit bunches per palm is not reduced to an appropriate level, the next year’s production will be low, and consequently an alternancy phenomenon is established.
Another advantage of bunch removal is to keep a proper balance between the number of leaves and fruit bunches. According to Nixon (1966), a Deglet Nour adult palm, along with other long-strand varieties, pruned to 100 – 120 leaves (a ratio of eight to nine leaves per bunch) is able to give satisfactory yield without an alternancy phenomenon.
The number of fruit bunches for a palm to carry safely is dependent on its age, size, vigour, variety and the number of good green leaves it carries: None for the first three years (at this age, growth is more important than fruit production until the palm is well established); one or two in the fourth year, three or four in the fi fth year and so on.
Depending on variety and growing conditions, full production accompanied with the maximum number and size of leaves is usually reached at 10 to 15 years and then about 10 bunches per palm can be allowed.
Bunch removal is practised immediately after fruit set. Priority, of bunches to remove, should be given to the following:
& # 8211; bunches with a poor fruit set;
& # 8211; early and late bunches: generally are small, poorly pollinated and located at the lower and higher position of the inflorescences production level;
& # 8211; bunches that are high in number on one side of the palm (their removal will ensure equilibrium for the palm); e.
& # 8211; bunches with snapped fruitstalks or broken strands.
Fruitstalks of bunches to remove must be sharply cut at their base (departure point from the stipe); the operation is usually performed with a single cut, since the fruitstalk is relatively tender at this stage.
3. Leaf-fruit bunch ratio.
An adult Deglet Nour palm, pruned to 100 – 120 leaves, is able to annually carry 12 to 15 moderately thinned fruit bunches without any alternancy phenomenon; the leaf-bunch ratio is 8 to 9 leaves for each fruit bunch (Nixon and Carpenter, 1978). Similar results were obtained with Zahdi cultivar in Iraq (Hussain et al., 1984). A grower is advised to take into account the variety, the state of his palms and existing cultural conditions before determining which leaf - bunch ratio to adopt.
It is worth mentioning that it is a complicated operation since the value of the leaf to the palm declines with age and no two leaves are of the same age. Furthermore, leaves 4 years old are only about 65 percent as effi cient in photosynthesis per unit of area, as leaves 1 year old (Nixon and Wedding, 1956). Under good cultural conditions, a leaf can support the production of 1 to 1.5 kg of dates. Regardless of the leaf-bunch ratio, several factors may affect fruit production: i. e. lack of fertilisation and insuffi cient irrigation which may reduce the number of fl ower clusters and limit the bearing capacity of the palm.
How to determine the number of leaves per palm.
Leaves are grouped in 13 nearly vertical columns, spiralling slightly to the left on some palms and to the right on others. The grower must only count the number of leaves in one of these columns and multiply by 13. According to Nixon and Carpenter (1978) and in order to allow for uneven pruning at the base, counts could be made on opposite sides and divided by two (Chapter 1; Figure 4).
4. Bunch lowering and support.
With most commercial date varieties, after the pollination season, the bunches are pulled downwards through the leaves, gently enough not to break any of the strands, and the bunch fruitstalk is tied for support to the midrib (leaf rachis) of one of the lower leaves to avoid breaking. This operation is executed when the fruitstalk is fully extended (long enough) but still fl exible to permit some of the curvature to be distributed, so that the base will not take all the stresses. This also makes the bunch easily accessible for thinning, bagging and/or pesticide application.
Tying could be done with twisted frond leafl ets, with rope or with twine (Figure 73). It also prevents damage caused by scarring and shattering of the fruits during high wind, and lessens the later danger of fruitstalk breakage by supporting the bunch as the weight increases (Nixon and Carpenter, 1978).
After the pollination season, some of the smaller and later bunches are not always old enough to tie when the earlier and larger bunches are ready for such an operation, and could thus be tied 3 to 4 weeks later. In general, the fruitstalk grows rapidly during the first few weeks after pollination and shows pliability and high bending capacity. When elongation ceases, breakage and obvious loss of the fruitstalk is to be expected (Figure 74). Usually, the bunch does not require support until the fruit has attained about 3/4 of its full size. When the fruit bunch ripens, it could quite easily reach a weight of 35 kg or more. It is worth mentioning that bunch management of soft date varieties should receive more attention than that of the dry date varieties.
With young palms, bunches are held off the ground by attaching the fruitstalk to one end of a wooden stake (with a fork shape, called pole) (Figure 78).
Date palm bunch covers offer several advantages and are commonly used in the New World of date culture areas in order to protect fruits from high humidity and rain, from bird attacks and also from damage caused by insects.
Protection from high humidity and rain.
In various date growing areas (USA, Algeria, Tunisia, etc. in the northern hemisphere; and in Namibia, RSA in the southern hemisphere), rain could coincide with the ripening season and consequently causes severe loss of fruit. A sturdy light-brown craft-paper is used in the USA to cover and provide good protection of the bunch during the ripening season (Figure 32).
Protection is applied to the bunches in late kimri stage. Paper covers, wrapped around the bunch and tied to the fruitstalk, could be used in combination with a pesticide programme because the lower part of the bunch is not covered. Covering bunches too early may lead to the sunburning of the outer young fruits, once the cover is removed.
With varieties such as Khadrawy and Hallawy having a relatively open crown, white paper covers have been found to cause less sunburn than brown paper covers. Medjool bunches are usually protected with a lightweight white cotton bag of which the upper portion is water-proof. Plastic bags are to be avoided because of sunburn and heat damage to the fruit as well as build up for humidity.
Wet weather resulting from very high humidity and/or from rain will produce various levels of damage depending on the fruit ripening stage:
Immediately before the Khalal stage, minute superficial breaks, or checks in the fruit skin occur. The abundance of these checks and their types (transverse, longitudinal or irregular) vary in different varieties. When the checking is severe it is usually followed by a darkening and shrivelling of the tip (blacknose).
At the Khalal colour (yellow to red), checking no longer occurs and water will produce deeper and longer breaks or cracks (splitting phenomenon) in the skin and fl esh beneath. Furthermore, humid weather during the Khalal stage also favours the attack by various fungi causing serious spoilage from rot.
At the Rutab stage, moisture no longer causes skin breakage, but the fruit absorbs moisture and becomes sticky, less attractive and more diffi cult to handle. High moisture content of the fruit will result in fermentation and souring that often results in heavy losses.
At the Tamar stage, high humidity and rain cause little damage to the fruit except when it is neglected. The timing of bunch protection from rain is usually when the fruit starts to acquire its Khalal colour. An early covering will increase checking and blacknose because it reduces ventilation within the bunch. Although, the fruits escape damage by actual wetting, damage by excessive humidity increases.
Protection from birds.
Birds of various species cause severe damage by eating on the fruit during the Rutab and Tamar stage (Figures 75 and 76). Parrots, besides eating the fruits while on the bunches (mostly at the Khalal stage), kick the fruit off the bunches with their legs, resulting in the loss of date fruits that fall to the ground.
Bird attacks are common in Sudan, Sahel countries and also in the southern hemisphere (Namibia, Republic of South Africa, for example). The most common birds causing damage to date fruit in Namibia and RSA are the Redbilled Quelea (Quelea quelea), Redheaded Finch (Amadina erythrocephala), Lesser Blue-Eared Starling (Lamprotornis chloropterus), and the Redeyed Bulbul(Pycnonotus nigricans). The Grey Lourie (Corythaizoides concolor), Rupell’s Parrot (Poicephalus rueppellii), and the Rosyfaced Lovebird (Agapornis roseicollis).
When there is danger of severe bird or/and parrot damage, it is advised to initiate a bird control system. With the paper bags, the bunch should also be protected beneath with a good grade of porous cloth or netting that will exclude birds and insects, but at the same time not interfere seriously with ventilation of the fruit.
The importance of ventilation increases during the later stages of fruit growth and ripening as well as with the frequency of showers and periods of high humidity. If such conditions occur, it is advised to use a cover flared out and not extending down around the sides of the bunch. The thinning of central-strands of a bunch will promote better aeration of fruits. Rings or spreaders 15 to 30 cm in diameter, made usually of heavy wire, could be inserted in the centres to keep the bunches open as the fruit becomes full sized. Such accessory is mainly recommended with short-strands varieties, bearing fairly soft fruits. Those of a many-pointed star shape (or corrugated wire) remain in place better than circular ones and they must be inserted before the fruit reaches the Khalal stage.
Protection from insects.
The bags retain the fruit and provide some protection from birds, but they do not hinder fruit-infesting insects (Carpenter, 1981). Unless only Khalal fruit is harvested, insects may damage more than 50 % of the Rutab fruit. Stored dates from such palms will show large infestation by living and dead insects.
Physical exclusion of most insects by use of screen bags is a practical measure used in various localities in the Middle East (Carpenter, 1975). Moths and other insects larger than fruit beetles(Nitidulidae) are excluded. The bags are of flexible 18 × 20 mesh wire or shade net (80 % is recommended) and are 1.0 to 1.5 m2, depending on the bunch size to be covered (Figure 77). It is closely tied to the fruitstalk to ensure that rain water will not enter and also to prevent it from being blown away by wind. The best timing of its placement is mid-to-late chimri stage.
The date grower is advised to conduct proper insect control in the field, followed by prompt fumigation of fruits immediately after harvest. Packing house sanitation is closely related to field insect control. The packing facility should be insect-free to prevent re-infestation of fumigated fruit by “Dried fruit-infesting insects”, flies, roaches and other pests.
Furthermore, the bags eliminate the need for pesticides on fruit and thus maintain biological control of Parlatoria scale and other insects.
To avoid confusion, one should differentiate between pruning in general terms and pruning in date palm. Pruning in fruit trees and bushes of temperate fruit consists of the removal of living wood, while pruning in date palm is in general the removal of only dead, or nearly dead fronds and their bases (Figure 79). Depending on variety and cultural conditions, date palm leaves can remain alive for at least seven years with a maximum activity during the first year and an ultimate decrease in their photosynthetic capacity. As the leaves do not drop of their own accord, they must then be cut off.
Pruning is desirable in order to improve date fruit quality and also enhance the bearing capacity. In fact, when too many leaves (as many as 180 leaves/palm unpruned for 5 to 6 years) are retained and reaching below level of the fruit bunches, a high percentage of fruit affected with checking and blacknose and of fruit in the dry grades is obtained. Checking, occurring during mid-summer, is increased by high relative humidity caused by lower leaves. Furthermore, such lower leaves probably compete with the fruit, and create favourable sites for diseases and pests. Removing the leaves up to about the point where the lower ends of most fruit bunches are exposed is highly recommended for adult full bearing palms.
Pruning is mainly practised after fruit harvest; Pruning could also be realised at any convenient time between the harvesting and the flowering season (thinning period is recommended) and because of the greater ease in cutting, it is desirable to remove them before the bases became hard and dry. The dry, old hanging and withering or diseased leaves are cut along with superfluous offshoots. Leaf pruning could also be synchronised with tying down of bunches or with bagging. It is recommended that leaves which are still green are not pruned so as to take full advantage of photosynthesis. Considerable evidence shows that, other conditions being equal, the fruit bearing capacity of a date palm is in proportion to the number of green leaves it carries.
During the pruning operation, unwanted offshoots should also be removed to foster growth of those that are retained on the palm for propagation, to make access to the palm easier and to promote growth and bearing of the parent palm. In very dense offshoots growth, some of the small plants may be seedlings rather than true offshoots, and must be discarded.
However, where there is any fear of frost in the coming winter, no pruning is recommended and the leaves are left for the protection from the cold of the young tender leaves.
Another important pruning process is the removal of spines, also called thorns. It is advantageous to annually remove spines from the base of new leaves in order to facilitate pollination and handling of fruit bunches. Cut thorns themselves are a source of some danger, because they lodge in leaf bases on the soil where they persist as a hazard.
Date spines are usually removed from the new growth of fronds in the crown of the palm just before the pollination season to allow easy access to the date spathes as they emerge. If the palms have been dethorned the previous year, the new growth will be 2 or 3 rounds of fronds, each round developing 13 new leaves, a total of about 26 to 36 fronds to be dethorned. Such an operation will ensure a safe approach to the spathes for their pollination and also avoid any risk of injury to labourers during other technical practices (tying down, protection of bunches, harvesting, etc.)
It is common to use dethorning knives of various designs to remove these spines: a long sharp curved blade or pruning knife mounted on a wooden handle 30 to 45 cm long, or a sickle type blade with a sharp cutting edge.
Figure 64. Pollination technique using two to three male strands.
Figure 65. Hand pollinator in use in Zagora, Morocco.
Figure 66. Scheme to show various components of the hand pollinator.
Figure 67. Drying of male spathes in a shaded and moisture-free area.
Figure 68. Mechanical pollen extractor and collector.
Figure 69. Dessicator used for long term pollen storage.
Figure 70. Storage of date pollen at low temperatures: (-4°C down to -18°C).
Figure 71. Even at low temperature storage, a dehydrating agent (calcium chloride) is needed.
Figure 72. Thinning methods:
A & # 8211; Removal of the lower one third of the bunch.
B & # 8211; Removal of entire central strands.
Figure 73. Bunch support using a twine.
Figure 74. Breakage of non - supported bunch.
Figure 75. A non-protected fruit bunch showing the damage caused by birds.
Figure 76. Fruits damaged by birds that eventually dry out and fall on the ground.
Figure 77. Shade net bags used to protect date fruit from birds and insects attack, (Right: 60 % and left 80 %).
Figure 78. Support of bunches on a young date palm using a fork shaped wooden stake.
Figure 79. Pneumatic tool used for leaf pruning and fruit bunches harvest.
CHAPTER VII: DATE PALM IRRIGATION.
CHAPTER VII: DATE PALM IRRIGATION.
By P. J. Liebenberg and A. Zaid.
Date Production Support Programme.
This chapter describes date palm irrigation and aims to calculate water requirements of this species as well as schedule irrigation to ensure that the date palm gets the necessary quantity of water when needed.
Like any other fruit tree, date palm needs suffi cient water of acceptable quality to reach its potential yield. In Table 48 quantities of water made available to date palm around the world can be seen. It is worth mentioning that all these countries use fl ood irrigation, except for Israel, which uses drip irrigation.
Date palm irrigation around the world.
Table 49 shows differences in summer and winter requirements in Tunisia. Summer water requirements (July, August and September) are about 7,154 m3/ha, while only 4,372 m3/ha are needed for the winter period (December, January and February). Summer requirements are almost double the winter ones and constitute 1/3 of the total annual consumption. Note these values are made available to the trees through fl ood irrigation.
Differences in water requirements between different regions of the same country are common as illustrated in the case of Algeria (Table 50). The date growing area of the Sahara needs approximately 34,190 m3/ha/year, while Ziran region needs only 15,000.
Water quantity consumed per ha of Deglet Nour date palm at Tozeur (Tunisia)
Approximate water requirements of date palm at different regions of Algeria.
2. Factors influencing water requirements.
It is necessary to take certain aspects into consideration in order to calculate the volume of water required by a palm. The following aspects play a major role in this calculation:
uma. Soil salinity: If the soil is saline, more water must be given to enable a leaching process for clearing the salt from the soil.
b. Temperature: The higher the temperature, the higher the rate of evaporation and the more water the plant needs.
c. Humidity: The lower the humidity level, the more water needed.
d. Wind (speed and occurrence): Higher constant wind speeds cause higher evaporation and thus higher water demands.
e. Cloud cover: More water is required during periods of less cloud cover.
It is worth mentioning that all above factors infl uence evapotranspiration, which strongly determines the water requirements.
Irrigation is the timely application of water to a crop in need of water. Any water applied when not necessary, is a waste of a precious commodity. For example: if water is applied too late in the season, then it is useless because the crop is already dead or the production suffered so much that there will be no fruit, even though defi cient water is then applied over the growing period. The opposite is also true; if too much water is applied, the plant may also suffer. The crop may die due to waterlogging. Usually date palms do not suffer from too much water although, as illustrated, i t is possible in uncontrolled fl ow from artesian wells at Qatif, Saudi Arabia (Dowson, 1982). It, will however, still be waste of water, as the farmer could use this water to irrigate other palms or crops.
Irrigation must take place where the roots of the plant can easily reach it. It is of no use to the plant if water is applied where the roots cannot reach it. Let us look at the root development of a date palm tree. If the soil is divided into four layers of equal depth from top to bottom, 40 % of all roots can be found in the top layer, 30 % in the second layer, 20 % in the third layer and the remaining 10 % in the last layer. The same percentages apply in concentric rings around the plant (Figure 62). The same percentage of water will also be extracted from the soil in the different layers due to the presence of the roots in these respective layers.
For mature date palms, the depth is about 5 m, and 3 m radius around the trunk. Thus, it is seen that for dates 40 % of all water is extracted from the first 50 cm, 70 % is from the first 100 cm, 90 % is from the top 150 cm and only 10 % is from the last layer or 150 to 200 cm and deeper. For young date plantlets this depth can vary from 25 to 50 cm and the radius from 10 to 30 cm, depending on the size of the plant. This means that the irrigation water must be applied within these boundaries to enable the plant to reach it. However, it is important to apply water be applied in such a way that it does not reach the deeper soil levels in order to ensure proper root development of the date palms.
Localised irrigation (e. g. drip and micro) will therefore be more effi cient than non - localised one (e. g. fl ood irrigation).
After planting small tissue culture-derived date palms, the volume of soil from which it can extract water is very small. If a person is not careful, suffi cient water may be applied, but not enough will be available to the plant for optimum growth. It is thus necessary to ensure that enough water reaches the area where the roots are. Irrigation must preferably be done by basin, micro or drip methods. Due to the shallow root depth at this stage, frequent irrigation is also necessary to ensure that the palm does not suffer from water deficiency. Even more care should be given if the palm is planted in a very sandy soil.
Different irrigation techniques are available to irrigate crops, but not all of them are suitable for date palm irrigation. The following methods are of importance and each has its own advantages and disadvantages:
uma. Flood irrigation.
This irrigation method is the oldest method known, and is also the method most widely used in date palm culture. It has, however, advantages as well as disadvantages which are outlined below:
(1) running costs are low;
(2) easy to apply; e.
(3) initial costs are low if the area is fairly flat.
(1) diffi cult to achieve a high effi ciency rate;
(2) labour intensive;
(3) irrigates areas in between where no palms are planted; e.
(4) not well suited for sandy soils.
b. Furrow and basin irrigation.
It is basically a redesign of fl ood irrigation to eliminate some of the disadvantages listed above and thus make it more effi cient.
(1) running costs are low;
(2) easy to apply; e.
(3) initial costs are low if the area is fairly flat,
(1) labour intensive; e.
(2) interferes with mechanical operations.
c. Sprinkler irrigation.
This is the oldest modern irrigation method and was introduced to enhance effi ciency and to enable automation.
(1) more effi cient use of water is possible;
(2) easy to schedule – manage;
(3) less labour is needed; e.
(4) tpography is not a limitation.
(1) expensive (installation);
(2) running costs are high;
(3) heavily influenced by wind and temperature (spray pattern and evaporation);
(4) not well suited for small palms because water can enter from above into the growth point of the palm.
d. Micro irrigation.
This method was more recently introduced and was developed in South Africa to irrigate mine dumps to prevent the wind from blowing the sand away. It was then adapted for irrigation of trees and other crops.
(1) more effi cient use of water is possible;
(2) running costs are lower than sprinkler irrigation (lower pressure needed);
(3) easy to schedule – manage;
(4) only areas that need water are irrigated;
(5) topography is not a limitation;
(6) It is easy to automate;
(7) It is not labour intensive; e.
(8) several spray patterns are available to suit date palms (e. g. gaps in the spray pattern so as not to wet the growth point or the trunk of the palm.)
(1) Installation costs are high;
(2) needs clean water; e.
(3) infl uenced by wind and temperature (spray pattern and evaporation).
e. Drip irrigation.
This is the latest irrigation method introduced and was developed in Israel where there is scarcity of water (Figure 62).
(1) more effi cient use of water;
(2) running costs are low;
(3) easy to schedule/manage;
(4) topography is not a limitation;
(5) only the water needed by the palm is applied;
(6) not infl uenced by wind;
(7) easy to automate; e.
(8) not labour intensive.
(1) expensive (Installation);
(2) requires very clean water; e.
(3) sometimes difficult to determine if the correct amount of water has been applied by the system, and when it becomes clear that it is too little, it may be too late.
4. Methods for calculating date palm water requirements.
From the earliest times, different methods were used to calculate the water requirements of different crops. As a result, numerous methods have been developed and adopted for date palms. Some of these methods are more accurate than others and some more convenient to use than others, because of the availability of information for the site where the date trees will be planted. The following are a few of the methods available:
& # 8211; Evapotranspiration/Class A Pan Method;
& # 8211; Blaney-Criddle Equation; e.
& # 8211; Solomon and Kodama’s Equation.
uma. ETP Class A Pan.
In Israel, USA and Southern Africa, the evapotranspiration/Class A Pan Method is frequently used because the needed information, is readily available.
AWR = Amount of water required during period under observation.
ETpan = Evaporation for period in mm as measured with Class A Pan.
CFpan = Crop Factor for that period.
h = Efficiency of irrigation system (in decimal).
Table 51 shows in more detail the calculations done to forecast water requirements of the palms for the 12 months of the year and using different irrigation methods for Naute – Namibia. (Note that this is for the Southern Hemisphere harvesting period is March to April)
b. Revised Penman-Monteith Method.
The Penman method is widely accepted as the most accurate method of calculating water requirements for crops. This method makes use of daily climatic information (e. g. maximum and minimum temperatures, wind velocity, humidity and radiation per day) to calculate the reference evaporation ETo. Due to the relative complexity of the formula, it is best used with the help of a computer program. The reference crop evaporation (Eto) is first determined and then the water requirement is calculated using the following formula:
kc = Crop Factor.
Eto = Reference Evaporation mm/day.
Etcrop = Crop Evapotranspiration mm/day.
ETcrop = kc * ET0 [mm/day]
In Tables 52, 53 and 54, calculations done with Cropwat 7 can be seen. Cropwat 7 is a computer programme based on the revised Penman-Monteith method, to calculate crop water requrements (Smith, 1992)
Water requirements for date palm at Naute, Namibia.
Flood Irrigation ® h = 60%
Micro Irrigation ® h = 85%
Drip Irrigation ® h = 90%
i – This is an estimate according to some desk study by the authors of this chapter – 1989.
ii – Use this crop factor only with class A evaporation pan fi gures.
Monthly reference evapotranspiration (revised Penman Montheith)
Crop evapotranspiration and irrigation requirements.
From tables 51 & 54 it is clear that the date palms at Naute (Namibia) need between 2,157 and 2,419 mm Nett irrigation per annum to fulfi l their needs.
As mentioned earlier, the date palm needs suffi cient water of acceptable quality to enable it to reach its full yield potential. To reach this aim, if all agricultural practices are catered for, (except water), then the average electric conductivity of the soil (ECe) must not exceed 4 dS/m (Ayers and Westcot, 1985), and that of the water (Ecw) not 2.7 dS/m. If situations occur where these values are exceeded then leaching must be practised to overcome this problem. However, due to the scarcity of water or the high cost of water, it will not always be viable to meet the leaching requirements. In such a case it may be viable to opt for a lower yield which may be more economical. In Table 55, ECe and ECw values corresponding to % of yield for date palm are shown.
ECe and ECw values corresponding to yield percentage.
However, to calculate the quantity of water needed for leaching, the following formula is used:
LR = Leaching Requirement (fraction).
Ecw = Electric conductivity of the water (dS/m).
Ece = Electric conductivity of the soil at % yield to be obtained (dS/m).
This quantity of water is over and above the nett irrigation required by the crop during the season. The total annual requirement is then calculated from the following formula:
AW = Depth of water supply (mm/yr).
ET = Total annual water demand (mm/yr).
LR = Leaching requirement.
Once it is known how much water to apply, it is also important to know when to apply it. To determine this, knowledge of the type of soil and how deep it is, is required. This gives an indication of how much water is in the soil and how much is available for the palm. This information, combined with the daily usage of water by the palm, enables the determination of when the next irrigation cycle is due.
The following fi gures are mean values of available water for the three major soil types:
Light soils – 100 mm/m.
Medium soils – 140 mm/m.
Heavy soils – 180 mm/m.
The best approach is to determine, through laboratory tests, the water holding capacity of the specifi c soil under consideration and then to establish an effective scheduling program.
To ensure that the palm will not be put under water stress, it is the normal practice to allow for only a fraction of the available water to be extracted. For date palm, as illustrated below, this fraction equals 0.4 or 40 % of the available soil water.
The water usage of date palm for a certain period is 8.7 mm/day. Table 56 shows that the available water for the soil is 140 mm/m depth. The rooting depth of a full grown date palm is 2 m. Portanto:
Available water = 2 × 140 = 280mm.
Extraction allowed = 0.4 × 280 = 112mm.
Cycle period = 112 ÷ 8.7 = 12.87 days. 13 days (Practically)
In Tables 57 and 58, an example of a fi xed scheduling programme can be seen for date palm at Naute (Namibia) as done by Cropwat 7. For this example, note that no rainfall is taken into consideration.
CROPWAT 7.0 (The information in the last column is only valid for fl ood irrigation.)
Water requirement using cropWat 7.
7. Layout of date palm orchard and irrigation.
The spacing between date palms differs worldwide. This can be ascribed to differences in variety as well as climatic conditions. In Namibia, the trend is to a 10 × 8 m spacing, 10 m between rows and 8 m in the rows. Some private farmers also use a 8 × 8 m spacing but, it is not advisable to use a narrower spacing.
The usage of micro irrigation is recommended due to the sandy soils where date palm is commonly grown, and the efficiency of this type of irrigation. Care should however be taken that no water is sprayed into the crown of the small palm. To this effect, micro’s with a 300° – 320° spray pattern should be used. Furthermore, to optimise the efficient usage of water it was decided to change the type of micro’s during the initial growing period of the date palm to ensure 100 % coverage of the drip area (rooting area). As stated before, due to shallower rooting in the first years of development, a more frequent irrigation schedule is recommended during these years than in the later ones. From planting to year (4) the area covered is about 12 m2 and the flow rate 96l/h/palm, from year (5) to year (10) the area covered = 18 m2 and the flow rate 104 l/h/palm and from year ten the area covered = 28 m2 and the flow rate 156 l/h/palm (Figure 63). This bigger area covered in the initial years (0 -3 and 5 – 8) will lead to waste of water, but on the other hand it will serve as a leaching operation that will benefit the date palm as a whole. Due to shallower rooting in the first years of development a more frequent irrigation schedule is required in those years.
Figure 62. Drip area of adult date palm tree and root distribution.
Figure 63. Wetting pattern of Micro’s.
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ARCHAEOLOGICAL MODELLING.
So how does one test an archaeological predictive model or know how well a predictive model works? If you determine how well a model predicts its own input data, what does it tell you about that data or is it just a circular argument? A predictive model of say the locations of individual stores in a chain of stores would give associations with say population densities and transport routes. But what does that tell you about the individual stores, what they sell or the subtle effects of local planning policies, etc? If you have used the archaeological record (HER) or field walking data or archaeological excavation data to make a model, that model will tell you about the location characteristics of that data only. But does that data represent archaeology or past settlement?
Field walking . The results of the Breckland Survey (Suffolk) suggest a correlation between archaeology and artefact scatters. However, the results of the Shapwick Project suggest that the date of material on the surface may not always be a reliable guide to the date of the buried deposits below (see Gerrad. C. ‘Misplaced faith? Medieval pottery and field walking’ in, Medieval Ceramics volume 21, 1997). Further, work carried out in the Rhone valley in France, specifically in relation to archaeological predictive modelling, suggests that field walking results are not always a good indication of what is below the ground surface (see Verhagan. P & Berger. J, ‘The hidden reserve: predictive modelling of buried archaeological sites in the Tricastin-Valdaine region’ in the 28 th conference of the CAA, 2001, BAR 931).
Metal detecting . Responsible metal detectorists report their finds to the county archaeological unit. However, it is very rare that they report areas where they have detected but found nothing. In Norfolk (UK) there is a common perception that most metallic archaeological finds are found in the West of the county. Ergo, majority of Norfolk metal deterctorists work in the West of Norfolk, which strengthens this common view. In other words it is a self-fulfilling situation.
The archaeological record (HER). This tends to be a mixed bag of ad hoc data, subject to various biases such as planning polices (PPG16), the county’s relationship with metal detectorists, the annual budget of the HER officers, etc. As a result it is not easy to model across county or administrative boundaries. The archaeological record is primarily made up of metal detecting, field walking, archaeological excavation, historic buildings and random spot find data.
To produce a good archaeological predictive model, one needs a lot of input data to sample over a small number of categories within any environmental (or social) dataset to obtain sufficient statistical data with which to model with. In other words one cannot sample say 10 pottery sherds over an area with say 15 different soil characteristics and hope to obtain sufficient and reliable data about the relationship between the pottery sherds and the soil! In practice (especially with models that cover a large area) this normally means using the archaeological record (HER) to make the model as there is normally insufficient field walking, metal detecting or archaeological excavation data with which to do so.
So to reword the primary question; what does one use to test an archaeological predictive model? One important factor is if you are considering all archaeology or just archaeological settlements. As it is difficult to define exactly what constitutes the HER, when modelling all archaeology using the HER, you can only use the HER itself to test the model! This bypasses the need to define exactly what the HER is and what it represents (like individual stores within a chain of stores). For example, remove say a random quarter of the HER, produce a predictive model using the remaining three quarters and then see how well that model predicts the removed quarter.
However, if one is modelling archaeological settlement then the situation is more difficult. Not withstanding the doubts noted above, does a scatter of artefacts found by systematic field walking represent a domestic settlement, a temporary encampment or some sort of industrial activity? Further, domestic settlements can be based on an agricultural economy or a pastoral economy, which require very different environments.
Test pitting on a regular grid system has been quoted as a suitable method to test a predictive model. Another way would be to carry out extensive excavations within the high probability areas of a predictive map to see how well it predicts settlement. Of course a handheld GPS unit and a time machine would be an ideal way of testing a predictive model of archaeological settlement. The important thing is that any archaeological predictive model should be tested by an independent means. Thus, does anyone have any practical suggestions or comments on testing archaeological predictive models?
Big bucks or a big mistake?
Archaeological predictive modelling started in the 1980s and has grown into a multimillion dollar industry, used almost entirely for cultural heritage management. Interest in predictive modelling was given a considerable boost in 1981 when the US Bureau of Land Management issued an instructional memo, encouraging its use. However, two years later there was a consensus by archaeologists and cultural heritage managers that a lack of scientific rigour and inter-project consistency required a systematic re-evaluation of predictive modelling. This emerged in the form of a landmark publication by Judge. W & Sebastian. L (ed.), ‘Quantifying the Present and Predicting the Past: Theory Method and Application of Archaeological Predictive Modelling’, 1988, US Government Printing Office, America.
Despite the above cautions, some countries and some states in America have continued to rely on archaeological predictive modelling as part of their cultural resource management. For example, one American state has an archaeological predictive model that cost $5 million to produce but estimates that it saves that state $3 million per year by reducing the number of staff required to govern the cultural resources and it has also cut down on administration time (see Madry. S, Cole, M, Gould, S, Resnick, B, Seibel, S, & Wilkerson, M, ‘A GIS based archaeological predictive model and decision support system for the North Carolina department of Transport’, in Mehrer. M & Westcott. K (ed.), GIS and archaeological site location modelling , 2006, Taylor & Francis, London).
In the 1990s, the Dutch government proceeded with a national archaeological predictive model, called the IKAW (Indicatieve Kaart Van Archeologische Waarden), probably because it was estimated that about a third of all archaeology in the Netherlands has been lost since 1950 due to development! The IKAW is now in its second generation and used extensively for cultural heritage management. The resultant map is divided up into high, medium and low areas of predicted archaeology and the policy regarding what action to take with a building development application within that area is defined (see Leusen. M & Kamermans H, ‘Predictive Modelling for Archaeological Heritage Management: A research agenda’, Nederlandse Archeolgische Rapporten 29, 2005, Amersfoort, Holland).
One of the biggest criticisms about archaeological predictive modelling used for cultural heritage management is that the models are self fulfilling. For example, for a building development within a high probability area, an archaeological excavation is likely to be demanded but within a low probability area, only a desk study is likely to be required. Thus, if you only look in a high category area, you will only find archaeology within that area and conversely if you do not look in a low category area, you will never find any archaeology within it!
One can understand the lure of archaeological predictive modelling to cultural heritage managers. It is the Holy Grail of their job! They develop an archaeological predictive map of the area they are responsible for, save a fortune by getting rid of all the regional archaeologists, simply plot any building development application on the predictive map and then issue the appropriate letter stating what archaeological action is required.
Do you agree with the above assessment or do you feel that I have over-simplified or misinterpreted the situation? I would appreciate your thoughts and comments on this sensitive subject.
So why are my predictive models not as powerful as other predictive models?
‘Gain’ is the accepted way of determining (and stating) the effectiveness of an archaeological predictive model, the higher the gain the better the model. In America it is considered that the maximum gain for a predictive model is probably restricted to around 70% due to inherent modelling problems and typically gains range between 50 – 70% (see Ebert. J, ‘The state of art in inductive modelling: seven big mistakes’, in Wescott. K & Brandon. R (ed.), Practical Applications of GIS for Archaeologists: a predictive modelling toolkit , 2000, Taylor & Francis, London). Typically the gains of my models are around 15 – 25% for predicting the model’s own input data and independent test datasets. So the question is why – what am I doing wrong?
As I live in Norfolk (UK), I’m currently developing my predictive modelling skills by modelling Norfolk only, with a view to expanding to the whole of East Anglia (UK) when I am proficient in the art. Oscar Wilde once said that Norfolk is very, very flat and I think that this is a clue – terrain! If one works within a landscape which funnels people to live in specific areas or the environment bars them for living in other areas, then modelling becomes easier. A classic example would be Egypt where the only place people can easily live (in the past or in the present) is next to the Nile (or an oasis) because of the water supply, fertile soil, wild life, etc. Any settlement away from the Nile (or an oasis) would require significant support from elsewhere.
Another factor is ground slope. A classic example is a predictive model in West Virginia (America) that produced high gains in a study area where 90% of the terrain is over 18° and 41% is over 31° (see Lock. G & Harris. T, ‘Enhancing Predictive Archaeological Modelling: Integrating Location, Landscape and Culture’ in Mehrer. M & Westcott. K (ed.), GIS and archaeological site location modelling , 2006, Taylor & Francis, London). Whilst foraging and hunting for food is possible in such a terrain, farming and building permanent settlements on flat ground is severely limited. Consequently, such terrain is ideal for hunter-gatherers who by their migratory life-style leave little evidence of their existence.
Compare these environments with Norfolk (UK); 90% of the county has a ground slope of less than 4° and as a consequence nowhere is very far from a source of open water! For comparison; in 1989 an archaeological predictive model comprising of 120 Km² of the Netherlands (the Regge Valley) was produced. Afterwards, the model was tested by intensely field walking a 2 Km² area within the study area and the settlements discovered were compared with the predictions of the model. The model achieved a high gain for predicting its own input data but a relatively low gain for predicting the field walking discovered settlements (see Brandt. R, Groenewoudt. B & Kvamme. K, ‘An experiment in archaeological site location: modelling in the Netherlands using GIS techniques’, World Archaeology 24: 2, 1992, Routledge, London). The terrain of the Regge Valley is similar to Norfolk and when tested, the Regge Valley model produced similar gains to Norfolk!
Concentrating on just one environmental factor – ground slope, I have examined sixteen published archaeological predictive models and have plotted their stated gain against the average ground slope of each study area (in some cases having to estimate it using various means such as Google Earth). Whilst it is not possible to consider that this plot shows a direct correlation between gain and ground slope (as there are numerous other factors involved) I have noted that the higher the average ground slope of the study area, the higher the gain is likely to be.
So, do I move to America in order to achieve models with higher gains to get my PhD or is it acceptable to carryout archaeological predictive modelling in any terrain? If you have any opinions on this subject I would be pleased to hear from you.
‘Environmentally Deterministic’ Predictive Models.
There are two main approaches to archaeological predictive modelling; inductive and deductive. Deductive modelling derives rules from theory or expert knowledge. For example, any settlement would want a close supply of water; therefore there should be more settlements near to open water sources. Inductive modelling derives rules from observations. For example, what is the percentage of known settlements within say 500m of a known open water source? For inductive modelling, the location of past settlement is predicted on the basis of various factors, which broadly fall into two categories; environmental and social. Environmental factors include; soil type, ground slope, etc. Social factors include; existing land ownership, defence, etc. Digital datasets for various environmental factors are readily available, although it is important to remember that they represent the present environment. Having said that, my interest is with the Anglo-Saxon period (410 – 1066AD) and I was surprised by how little overall climatic variation there has been since then (see Lamb. H, ‘Climate: present, past and future’ – volume 2, 1977, Methuen & Co, London). Further, digital soils data (such as fertility, etc) quote ‘base’ properties which do not include for artificial fertilizers or drainage. Thus, suggesting that they are ‘timeless’ properties.
Unless you are modelling the documented past, digital datasets for social factors do not exist and are virtually impossible to make due to a fundamental lack of historical information. One can theorise about social factors but you soon get into all sorts of arguments and counter arguments, which end up with you guessing! For example, during the Anglo-Saxon period the East of England was subjected to raiding from across the North Sea. Therefore, living next to the North Sea or an estuary leading into it would have been precarious. However, in times of peace, these locations make ideal places to settle due to their natural resources and trading links. It all depends upon how large a threat this raiding was perceived at that time.
The degree to which social and environmental factors influenced site location is one of the purposes of academic predictive modelling. Some theoretical settlement models assume the specialization and inter-settlement exchange of local produce (see Aston. M, ‘Interpreting the Landscape’, 1999, Routledge, London). However, majority of settlements would still need to be self sufficient to a reasonable degree; else they would be a significant drain on the resources of their beneficiaries. Thus, environmental factors would still play a significant part in the choice of settlement location. Further, technological advances (such as transport, soil improvement, etc) expand the type of terrain suitable for settlement as it reduces the need for self sufficiency.
So, should archaeological predictive modellers simply ignore all social factors on the assumption that environmental factors over shadow them? If not, then how does one go about determining social datasets to use in archaeological predictive models? I feel that this issue deserves more debate and I would be interested to hear from anyone with a view on this difficult subject.
I’m a PhD student at the University of East Anglia (UK) studying Landscape Archaeology. My research is on the distribution of archaeological artefacts and settlement in East Anglia, concentrating on the differences between early, middle and late Anglo-Saxon periods. I’m interested in the environmental factors which affected the positions of settlement between these historic periods and to search for areas of abnormally high or low concentrations of archaeology. The datasets and techniques I use are identical to those used for archaeological predictive modelling, which some countries and regions incorporate into their cultural heritage management (CHM) strategies. The use of these techniques for academic research is normally not criticised but their use for heritage management is.
Article 5 of the Valletta Agreement (1992) states that; ‘Governments have a duty to see that the interests of archaeology and of development are judiciously weighed against each other’. As a result, some countries have turned to archaeological predictive modelling as part of their cultural heritage management. For inductive predictive modelling, the location of archaeology artefacts and settlement is predicted on the basis of various factors, which broadly fall into two categories; environmental and social. Whilst datasets for environmental factors are available, social datasets are not.
The main criticisms are that predictive models used for CHM are self fulfilling, environmentally deterministic and the datasets they are based on are biased. Exponents of their use for CHM say that such models same time and simplifies administration.
I feel that there should be a place to discuss (and hopefully reach agreement on) these fundamental differences and hence I offer this blog. If your research is in this area or you work in cultural heritage management and use such maps I would like to hear your views on this subject.