Storage efficiency of off-season irrigation

Water levels in the Ogallala aquifer are declining, and with the resultant decrease in water capacity of wells, irrigators face difficulty in meeting crop water needs. Off-season irrigation is common in the region, although research has shown it is often inefficient. Storage efficiency of off-season irrigation is affected primarily by the amount of water in the soil profile during storage. Because of much interest in off-season irrigation, our objective was to describe the relationship between water storage efficiency and soil profile water content. Through use of simulation results from a water balance model, we calculated net water gain on 15 May that resulted from fall or spring irrigation. Storage efficiency was related with the maximum of soil water (SW) from irrigation to 15 May. Storage efficiency was 90 to 95% of spring, or 80 to 85% of fall net irrigation amount, with SW in the lower half of the available water (AW) zone. As SW increased above approximate to 55% AW for fall or approximate to 60% AW for spring irrigation, storage efficiency decreased and approached zero with SW near 100% AW. This analysis will help producers understand water storage efficiency of off-season irrigation and how storage varies with SW.