Abstract: This research aimed to explore the effect of different phosphorus (P) fertilizer application rates on the yield and P use efficiency of alfalfa, and to determine the soil total P and available P levels and plant tissue P levels under the different P fertilizer regimes. P fertilizer rates applied in the experiment were (as P₂O₅ equivalent) 0 kg·ha^-1 (CK), 50 kg·ha^-1 (P₁), 100 kg·ha^-1 (P₂) and 150 kg·ha^-1 (P₃). The P fertilizer was applied together with irrigation water under drip irrigation, beginning at the branching stage of spring growth following winter dormancy, and subsequently 3-5 d after the first, second and third cuts. The maximum P concentration of leaves and stems was attained under the P₂ treatment. The P concentration of leaves was 0.223%, 0.275%, 0.292% and 0.218%, under CK, P₁, P₂, and P₃ treatments, respectively; and the corresponding P concentration of stems was 0.202%, 0.223%, 0.201% and 0.146%. Hence, the P concentration of alfalfa leaves was higher than the P concentration of stems. The hay dry matter yield and elemental P yield were also maximized under the P₂ treatment (6.54 t·ha^-1 and 13.78 kg·ha^-1, respectively). Soil total P concentration and available P concentration increased with increased P fertilizer. The P fertilizer treatments had significantly greater soil P than the CK treatment (P<0.05). The P use efficiency decreased with increased P application, and was highest (28.37%) in the P₁ treatment at the first cutting. The phosphorus uptake of drip-irrigated alfalfa was significantly positively correlated with the hay yield of alfalfa (P<0.01). In conclusion, for the P₂ treatment (100 kg·ha^-1 P₂O₅), and this treatment promoted absorption of soil available P by the alfalfa roots, improved the P use efficiency of alfalfa, and improved the hay yield.

Key words: alfalfa, phosphorus use efficiency, total phosphorus, available phosphorus, drip irrigation