Effects of deficit irrigation on yield and nutritive value of alfalfa varieties in Northern Nevada’s semi-arid environment

Increasing water demands and prolonged droughts are forcing many farmers in Nevada to grow alfalfa (Medicago sativa L.) under deficit irrigation (DI). While DI can increase crop water productivity (CWP), it can also lead to water stress conditions that reduce yield. This study assessed the effects of DI on yield, nutritive value, and CWP of two alfalfa varieties marketed as drought-tolerant (Ladak II) and highly productive (Stratica). An experiment was conducted at the Valley Road Field Lab in Reno, Nevada, over three growing seasons (2021–2023), in which the following three irrigation treatments were applied to both varieties: 100 % (full irrigation, FI), 80 % (mild DI), and 60 % (moderate DI) of replenishment of soil water depletion to field capacity. Irrigation amounts applied to each treatment were delivered by a surface drip irrigation system and calculated from volumetric water content measurements collected by soil moisture sensors based on time-domain reflectometry. Seasonal water use of each alfalfa variety and treatment was estimated using a soil water balance. Over the years, moderate DI decreased seasonal dry yield by 13.9 % and mild DI by 4.6 % compared to FI. The drought-tolerant variety produced similar yields to the highly productive variety when both received the same irrigation treatment. Irrigation treatment significantly affected (p < 0.01) the seasonal mean CWP across years, which improved under DI. Seasonal mean CWP increased from 11.5 kg ha−1 mm−1 in the 2021 season to 19.2 and 18.5 kg ha−1 mm−1 in 2022 and 2023, respectively. Across seasons, mean acid detergent fiber (ADF) was not affected by irrigation treatment, but neutral detergent fiber (NDF) (p < 0.001) and relative feed value (RFV) (p < 0.01) were significantly influenced by irrigation treatment. Forage nutritive value was not affected by alfalfa variety. These findings suggest that while DI could reduce alfalfa yield, it enhances CWP and can improve nutritive value, being a viable strategy under water-limited conditions. In northern Nevada’s semiarid conditions, a mild DI appears to be the best option for producers because it offers a balance between alfalfa yield, nutritive value, and potential water savings.