Water Budget Approach to quantify Cowpea Yield using Crop Characteristic Equations

Crop growth and yield as influenced by various environmental parameters are modelled for better planning and more efficient management of the crop production process. Many of the models currently used have complex input requirements. The objective of this study was to use soil water budget and simple relationships for evapotranspiration partitioning, leaf area index determination, and the transpiration functions for dry matter and for harvest index to develop a model for growth and yield production of cowpea under soil water stress conditions. The Food and Agriculture Organisation (FAO)–Penman and FAO–Penman–Monteith methods were used to estimate the reference crop potential evapotranspiration ETo and the results of the soil water balance accordingly were compared. The model was calibrated by a set of data from which the above relationships were derived and then validated very well with another set of data obtained from an experiment in the same area but in a different year. It was concluded that the FAO–Penman method for estimation of reference crop potential evapotranspiration is superior to FAO–Penman–Monteith method in the study area. The model is also capable of estimating dry matter production during the growing season. Furthermore, it was shown that the model can be successfully applied for farm irrigation management and scheduling. It was indicated that the optimum irrigation interval was 7 days with the amount of applied water of 5 cm for each irrigation event.