Irrigation technology, irrigation dose, and crop genetic impacts on alfalfa yield and quality

In water limited environments, alfalfa (Medicago sativa) is often criticized for its high water use, prompting interest in optimizing irrigation technologies, deficit irrigation, and drought-tolerant genetics. However, potential cumulative benefits from combining water-saving strategies have not been previously identified. This study evaluated the independent and combined effects of five irrigation technologies (low-elevation Nelson advantage, low-elevation precision application, low-elevation spray application, mid-elevation spray application, and mobile drip irrigation), four irrigation doses (growers’ typical full dose, a 25 % reduction, and two 50 % reductions, uniform and growth stated-targeted), and two alfalfa varieties (growers’ conventional and drought-tolerant) across three Utah sites from 2020 to 2022. No interaction effects were found among these factors, indicating that stacking multiple water-saving strategies did not enhance yield or forage quality. Low-elevation sprinkler technologies generally outperformed mid-elevation and mobile drip irrigation, though results varied by environment. Deficit irrigation at 25 % reduction often maintained yields similar to growers’ Full irrigation dose, while 50 % reductions consistently decreased yield by 22–54 %. However, deficit irrigation improved forage quality and water use efficiency. Decision tree models revealed that maximizing relative feed value-adjusted water use efficiency primarily depended on matching irrigation dose and technology to site-specific climate demand rather than applying Full irrigation. These findings suggest that moderate deficit irrigation and low-elevation sprinkler technologies can improve forage quality and water resource efficiency without substantial yield loss that occurs with 50 % deficit irrigation.