Optimizing water and phosphorus management to improve hay yield and water- and phosphorus-use efficiency in alfalfa...

Alfalfa (Medicago sativa L.) is an important forage legume in arid areas, but limited water resources and low fertilizer utilization have restricted its agricultural development. Meanwhile, studies on the effects of integrated water and phosphorus on production performance and water-use efficiency and phosphorus-use efficiency of alfalfa, especially on hay yield, phosphorus accumulation, and total phosphorus uptake are rarely reported under drip irrigation. The treatments were a factorial combination of three irrigation rates (5,250, 6,000, and 6,750 m³/ha per year) and four P rates (0, 50, 100, and 150 kg/ha per year) and consisted of 12 treatments for water and P management, arranged in a randomized complete block design with three replicates. Total hay yield and water-use efficiency and phosphorus-use efficiency of alfalfa in P₂ treatment were significantly greater than those in the P₁ and P₃ treatments (p < .05), and the total hay yield of alfalfa with phosphorus application increased by 7.43%-29.87% compared with that in the nonphosphorus (P₀) treatment under the same irrigation amount. The total phosphorus and available phosphorus concentrations in the 0-20 cm soil layer were greater than those in the 20-40 cm and 40-60 cm soil layers compared with those in the P₀ treatment. Correlation analyses showed that total hay yield was significantly positively correlated with total phosphorus uptake and water-use efficiency (p < .01). The accumulated phosphorus concentration was significantly positively correlated with total phosphorus and available phosphorus concentration (p < .01) and was positively correlated with the phosphorus-use efficiency (p < .05). The membership function method was used to evaluate all the indicators, and the three treatments that had the greatest influence on the production performance of alfalfa were, in order, W₂P₂ > W₃P₂ > W₁P₂. Therefore, an irrigation rate of 6,000 m³/ha and a phosphorus application rate of 100 kg/ha per year should be considered as the best management for both high yield and water-use efficiency and phosphorus-use efficiency of alfalfa.