As part of the objective of the case study, crop performance and yields obtained using two planting dates were compared to demonstrate the importance of using the climate forecast, i.e. planting date determined and rationalized by considering the advanced seasonal climate information versus the farmer's choice of planting date. Analysis of seasonal climate forecasts and the use of the historical data on normal precipitation alone suggested that the planting date could not be determined exactly. Thus, an alternative practical approach was to use the available historical rainfall data combined with statistical analysis to determine the distribution of the end of rainfall occurrence and to validate the planting date using crop simulation. The 42-year monthly rainfall data of Isabela were classified into El Niño, La Niña or neutral years leading to the classification of the October 2003-January 2004 corn cropping season as El Niño, La Niña or as neutral season. The historical end of the rainfall occurrence for the October-January cropping season for the grouped years was also determined. Planting date was determined such that the critical stage of corn growth should be synchronized with the period when there is adequate soil moisture so that crop yield will not be significantly affected or reduced. It has been reported that water stress or moisture deficit from tasseling/reproductive stage to maturity is the most critical stage of corn growth which significantly reduced corn yield (Shaw and Thom 1951; Coligado et al. 1963; Papadakis 1966; Classen and Shaw 1970; and Sys et al. 1993). This critical period is about 55 days after planting. Thus, the recommended planting date was obtained by determining the date such that the critical crop growth stage will not coincide with the period of moisture stress (i.e. about 55 days before end of rainfall occurrence). For both Naguilian and Benito Soliven, the recommended planting date is 21 October 2003. However, planting date for Benito Soliven was moved to 27 October 2003 due to technical tribulations. Unlike in Naguilian, farmers in Benito Soliven prepare their land manually (i.e. using animal-drawn plow) that requires longer number of days. Tractors are not used in this area due to its rolling terrain. Each planting date was further validated to be optimal for each site by crop simulation modeling using CERES-Maize model by simulating crop yields with the specified dates of planting as model input data.
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