Optimizing the nutritional quality and phosphorus use efficiency of alfalfa under drip irrigation with nitrogen and phosphorus fertilization

Appropriate fertilization is an important management practice for optimizing the nutritional quality and increasing the phosphorus use efficiency (PUE) of field‐grown alfalfa ( Medicago sativa L.). A 2‐yr field experiment in 2017 and 2018 in Xinjiang, China, involving fertilization with different amounts of N (0, 105, and 210 kg ha −1 , referred to as N 0 , N 1 , and N 2 , respectively) and P (0, 50, 100, and 150 kg ha −1 , referred to as P 0 , P 1 , P 2 , and P 3 , respectively) was established and resulted in the production of high‐quality alfalfa under drip irrigation. The crude protein (CP) content in the N 1 treatment was greater than that in the N 2 treatment under the P 0 , P 2 , and P 3 treatments. Compared with that in the N 1 P 0 and N 2 P 3 treatments, the relative feed value (RFV) in the N 1 P 2 treatment increased by 9−21% and 8−18%, respectively. The annual total CP yield in the N 1 P 2 treatment was the greatest. Compared with that in the N 1 P 3 treatment, the total PUE in the N 1 P 2 treatment increased by 76.69−99.69%. At each clipping, the CP yield and PUE of alfalfa were significantly different between the N and P treatments. Therefore, we conclude that when N was applied at 105 kg ha −1 and P was applied at 100 kg ha −1 , alfalfa presented the greatest nutritional quality and PUE under drip irrigation.