Deficit irrigation scheduling based on plant growth stages showing water stress tolerance

Abstract

With increasing municipal and industrial demands for water, its allocation for agriculture is decreasing steadily. The major agricultural use of water is for irrigation, which, thus, is affected by decreased supply. Therefore, innovations are needed to increase the efficiency of use of the water that is available. There are several possible approaches. Irrigation technologies and irrigation scheduling may be adapted for more-effective and rational uses of limited supplies of water. Drip and sprinkler irrigation methods are preferable to less efficient traditional surface methods. It is necessary to develop new irrigation scheduling approaches, not necessarily based on full crop water requirement, but ones designed to ensure the optimal use of allocated water. Deficit (or regulated deficit) irrigation is one way of maximizing water use efficiency (WUE) for higher yields per unit of irrigation water applied: the crop is exposed to a certain level of water stress either during a particular period or throughout the whole growing season. The expectation is that any yield reduction will be insignificant compared with the benefits gained through diverting the saved water to irrigate other crops. The grower must have prior knowledge of crop yield responses to deficit irrigation. This paper reviews yield responses of major field crops to deficit irrigation, including cotton, maize, potato, sugar cane, soybean and wheat. Crop yields obtained under various levels of reduced evapotranspiration were fitted to the linear crop yield response functions of Stewart et al. (1977). Results show that cotton, maize, wheat, sunflower, sugar beet and potato are well suited to deficit irrigation practices, with reduced evapotranspiration imposed throughout the growing season. This list may also include common bean, groundnut, soybean and sugar cane where reduced evapotranspiration is limited to (a) certain growth stage(s). With a 25 percent deficit, WUE was 1.2 times that achieved under normal irrigation practices. Irrigation scheduling based on deficit irrigation requires careful evaluation to ensure enhanced efficiency of use of increasingly scarce supplies of irrigation water.