Crop model evaluation of precipitation, planting date, and nitrogen application interaction effects on corn yields in Central America

Crop yield models are useful for estimating potential production, the effects of supplemental irrigation and other production aspects of agriculture. Crop and weather simulation models are powerful tools for developing strategies for increasing crop yields and reducing risks of crop failure in the developing countries where there is dependence on rainfed agriculture.; An incomplete gamma function was used to determine the probability of occurrence of the rainfall at the 5, 50, 75 and 95% levels using precipitation data of San Jose, Costa Rica from 1888 to 1972. The results were compared with probability levels estimated from WMAKER model.; The PLANTGRO model was used to compare relative yields predicted using WMAKER generated climatic data and measured daily climatic data. The measured and generated precipitation were used as input to the crop model.; The daily measured weather data from several years at 9 meteorological stations was selected to predict relative yield of corn using the PLANTGRO model. The values of relative yield of corn determined for each stations considering different planting dates were ranked to determine frequency of distribution. The different frequencies of distribution of relative yield of corn were examined to identify the optimum period of predicted planting date for different conditions of soil and length of season.; The interactions of irrigation and nitrogen on corn yield at San Andres, El Salvador were evaluated from values of predicted corn yield generated by the CERES-Maize model. High coefficients of correlation were found between actual and simulated yield values when previous adjustments of the model were made for various conditions.; CERES-Maize and NITWAT models were used to determine total N-uptake by the corn plant. The high correlation of values of N-uptake for both models means that either one of the models was satisfactory for determining N-uptake of nitrogen by the corn plant.; Simulated values of yield response to nitrogen applied at different times and for different planting dates were calculated using the CERES-Maize model during 17 years in order to evaluate the optimum number of applications of nitrogen. The highest yield response to N fertilizer was obtained when the fertilizer was applied on three separate dates during the wet season. (Abstract shortened with permission of author.)...