7. Crop Choices with Limiting Water Supplies: Deficit Irrigation and Sensitive Crop Growth Stages

Limited supplies of good-quality water in semi-arid and arid crop production regions often results in intense competition for water supplies among agricultural, municipal, and environmental interests. This increased competition can provide motivation for agricultural water users to reduce planted acreage, change practices or use equipment to control water losses, improve efficiencies of water application or irrigation scheduling, and consider changes in water management to impose some periods of deficit irrigation. Each of these choices has consequences for the crop, land and producer, the magnitude of which often depends on the knowledge of the agent making the choice as well as other factors outside of their control. For instance, if deficit irrigation is to be effective, it requires identification of growth stages sensitive to reduced water applications. Additionally, deficit irrigation requires development of new irrigation scheduling approaches that are based on a reduction of applications, at least during a large portion of the less-sensitive crop-growth stages. Crop species have different sensitivities to water deficit and, therefore, the potential impact on crop productivity (yield) will likewise be different. Crop-quality characteristics can also be adversely affected, some of which can impact marketability and the relative value of the crop. Objectives of this analysis are to describe crop and water management issues that can arise when deficit irrigation is considered as a water-saving approach. This chapter also provides examples of crop species characteristics that impact the suitability of deficit irrigation as a workable management option when irrigation water is scarce.