Effect of regulated deficit irrigation on alfalfa performance under two irrigation systems in the inland arid area of midwestern China

Irrigation plays a fundamental role in sustanining the productivity of agricultural systems in the inland arid area of midwestern China. Deficit irrigation can help to balance yield outcome and water input. Few studies have investigated the impact of deficit irrigation on alfalfa performance, which shows great differences from grain crops in water requirement and management strategy. The study aimed to evaluate the effect of regulated deficit irrigation on forage yield and quality of alfalfa (Medicago sativa). A three year trial was carried out with two irrigation systems (flood irrigation, FI and subsurface drip irrigation, SDI) and seven contrasting regulated irrigation treatments, and alfalfa growth, productivity and water use were measured. Under both irrigation systems, alfalfa forage yield decreased with decreasing irrigation amount under whole stage irrigation, while forage quality improved. However, the performance of alfalfa was different when deficit irrigation was applied at various growth stages. Compared with other deficit irrigation treatments, regulated deficit irrigation at single growth stage usually led to a higher yield. There was an exponential relationship between plant height and forage yield (R2 = 0.62 for FI and R2 = 0.57 for SDI) and a linear relationship between leaf area index and forage yield (R2 = 0.56 for FI and R2 = 0.64 for SDI). There was a negative correlation between forage yield and quality, which was closer to some quadratic relationships. Therefore, regulated deficit irrigation can help to achieve an ideal yield (up to 34.9 t/ha) and quality in this area. In the inland arid area of midwestern China, subsurface drip irrigation showed a higher irrigation water use efficiency (13.8–84.4 kg/(ha mm)) than flood irrigation (10.8–66.6 kg/(ha mm)) for alfalfa production. With limited water supply, deficit irrigation at single growth stage usually maintained a higher forage yield compared to slightly stressed irrigation during the whole growth. Deficit irrigation at the branching stage led to more negative effect on forage yield compared to other single stages.