Reducing peak supplemental irrigation demand by extending sowing dates

Supplemental irrigation (SI) is a common practice in the dry environments and aims at improving and stabilizing rainfed crops by adding small amounts of water to rainfed crops during times when rainfall fails to provide sufficient moisture for normal plant growth. Results from long-term research in experimental stations and farmer fields showed substantial increases in rainfed crop yields and water use efficiency in response to SI. Nevertheless, SI comes at a cost. The date of sowing winter wheat in a rainfed Mediterranean-type environment depends upon the onset of rainfall. The optimal date for achieving highest yield under rainfed conditions is around mid-November. However, farmers tend to sow wheat later than this date because of the delay and/or unreliability of initial rains. With SI, early sowing and crop establishment can be ensured. However, early sowing of all the fields’ results in higher water demand during a very short period in spring because all the fields will be at the peak use rate. Spreading out dates of sowing allows peak water demand to occur over a longer period, thus reducing the discharge and the size of irrigation system needed, and hence improves the economics of this practice. In this paper, the impact of adopting a multi-sowing date strategy on farm water demand and crop production is considered. A simplified optimization model solved by linear programming is presented. Four-years’ data (1992–1996) from field experimental research conducted on bread wheat in northern Syria have been used in the analysis.