Optimal irrigation water allocation and scheduling under a multiple cropping system

When seasonally available irrigation water is limited and/or expensive, it is important to use it in such a way that the total net benefit from the farm is maximised. In this study, a dynamic programming model was used to allocate (distribute) limited amount of water among four crops (cotton, maize, groundnut, and sorghum) in the Amibara area (Ethiopia). Economic coefficients, crops areas, crop growth stage stress effects and other climatic, crop, and soil parameters relevant to irrigation scheduling were inputs to the model. The water allocated to each crop was scheduled taking into account sensitivity of different crop growth stages assuming weekly irrigation interval. It was found that under multiple cropping system, it is advantageous to meet full water requirements of sensitive crops while satisfying the requirements of less sensitive crops only partially. About 40% increase in the total net benefit was observed by using 50% dependable rainfall instead of 80% dependable rainfall. Therefore, since rainfall varies from year to year considerably, irrigation plans have to be prepared for different levels of dependable rainfall and use the appropriate one during the irrigation season. The information can be of great importance in optimal irrigation water requirement under limited water allocation.