Evapotranspiration and Yield Impact Tools for More Water-Use Efficient Alfalfa Production in Desert Environments

Drought and climate change have decreased water availability for agriculture, especially in the desert of southwestern USA. Efficiency enhancements in irrigation management aimed at conserving water are key to adjust to limits in water supply, improve profitability and sustainability of alfalfa production in arid and semiarid areas. This study intended to conduct a field-scale analysis to develop yield and ET estimation tools for the effective use of irrigation water in a desert alfalfa production system. Extensive data collection and trials were carried out over three years in nine fully irrigated commercial alfalfa fields in the low deserts of California. The seasonal crop water consumption measured using the residual of energy balance method varied from 1381 mm to 1596 mm across the experimental sites and crop seasons. Variable seasonal dry mater (DM) yields ranged from 23.01 Mg ha(-1) to 29.90 Mg ha(-1). The results indicated that the first five cuttings each year were the most productive cuttings with a mean DM value ranged between 3.29 (cut 1) and 4.21 (cut 4) Mg ha(-1) but declined in later cuttings. An average annual water productivity (WP) value of 17.0 kg ha(-1) mm(-1) was determined across the sites varying from 15.5 to 18.9 kg ha(-1) mm(-1). The findings suggested that one may lose up to 1.44 Mg ha(-1) alfalfa yields with moderate summer deficit irrigation strategies, using 40% less water applied than full irrigation practices over the summer period of July-September. A more severe summer water deficit, with no irrigation event over the summer period of July-September may result in a potential water savings of 0.234-0.246 (ham) ha(-1) and 19-21% seasonal yield losses in the desert environment. This study describes the seasonal yield pattern, the crop water use-production function, and the crop coefficient values for various harvest cycles over the crop season. These tools may assist farmers to quantify water savings and estimate yield losses for more accurate and effective irrigation management strategies to meet water conservation objectives and for the resiliency of alfalfa production in the desert region.