Developing a Crop Water Production Function for Alfalfa under Deficit Irrigation: A Case Study in Eastern Colorado

Recent Colorado, USA water law provisions allow a portion of irrigation to be leased between agricultural and other users. Reducing consumptive use (CU) through deficit while maintaining some crop production could farmers earn revenue from leasing rights. This observational study aimed determine if alfalfa (Medicago sativa L.) can used reduce CU, provide parameters for an function (WPF), evaluate the potential improved farm income by water. Soil balance, evapotranspiration (ET), dry matter yield eight commercial fields (1.70 2.14 ha zones), growing subsurface drip-irrigated alfalfa, were monitored five seasons (2018–2022) at Kersey, Colorado. Four treatments [Standard Irrigation (SI) = irrigate when soil (D) exceeds management allowed depletion (MAD); Moderate Deficit (MDI) 70% SI; Severe (SDI) 50% Over (OI) 120% SI] applied, with two zones per treatment. Reductions in CU ranged 205 260 mm season. The shape WPF (dry biomass vs. ET) was concave, indicating that efficiency (WUE) optimized irrigation. average WUE 0.17 Mg ha−1 cm−1 tended increase greater deficits. also increased relative feed value. If conserved into transfer market, profit lease forgone production. We found incremental positive, assuming 2020 prices hay ($230 bale−1) above $0.50 m−3.