Modeling maize planting date to minimize irrigation water requirements

A mathematical model that uses daily maximum and minimum temperature data is presented for selecting the best planting day to minimize the total irrigation water required to grow corn. The model calculates the total seasonal irrigation water requirement by summing the daily crop evapotranspiration, ETc , soil moisture storage and deep percolation losses from the planting date to the harvest date. The planting date resulting in the lowest irrigation water requirement for the growing season was selected as the best date to plant the crop in order to maximize total irrigable area for the available quantity of irrigation water, or to minimize the required irrigation water for the given area. The model was used to simulate the seasonal cropwater requirements of maize using 1998-2008 daily weather data from a weather station in the Coastal Savannah zone of Ghana. The optimum planting dates were found to be between 15th March and 15th May, and the worst planting dates 2nd November and 14th January. The differences between irrigation water requirements between the optimum and worst planting dates were 57~95%, implying that up to about 95% more area could be irrigated without additional irrigation water through optimum planting date selection. The coincidence of the model optimum planting window with the indigenous planting time indirectly validates the the 1985-Hargreaves reference evapotrans- piration sub-model for this part of the world.