Maximizing the water productivity and economic returns of alfalfa by deficit irrigation in China: A meta-analysis

Alfalfa (Medicago sativa L.) is a high-water-use crop primarily cultivated in water-scarce areas in China. Deficit irrigation is still considered a promising strategy to improve regional water productivity (WP) despite the risk of yield loss. The objectives of this paper were to better understand the effects of deficit irrigation on alfalfa yield and WP via a meta-analysis, to quantify the relationship between alfalfa yield and crop water use and to identify water management practices that strike a balance between costs and returns in China. A total of 28 published papers covering 26 locations showed that deficit irrigation reduced alfalfa yields by 17.4% ± 1.2% and increased WP levels by 14% ± 2.5% relative to full irrigation. The yield and WP changes were significantly (P < 0.05) caused by the irrigation application rate and timing, soil texture, soil field capacity and soil organic matter. The application of deficit irrigation only at the budding stage effectively reduced alfalfa yield losses, with the lowest yield loss (8%) relative to full irrigation during the whole growth stage. In soil with a high bulk density (1.5–1.6 g cm−3), high organic matter content (>30 g kg−1) and sandy loam soils, the magnitudes of the effects on yield reduction were smaller than those on WP improvement. Both alfalfa biomass yield and WP exhibited a parabolic relationship with the crop water use. Based on an economic and trade-off analysis, a deficit level of 90% of full irrigation is recommended in semi-humid regions for WP maximization. Deficit levels of 80% of full irrigation and 60% of full irrigation are more appropriate in semi-arid and arid regions, respectively to maximize the net income per unit water.