Alfalfa (Medicago sativa L.) is an important forage legume in farming and animal husbandry systems. This study assessed the effects of arbuscular mycorrhizal fungi (AMF) and phosphate-solubilizing bacteria (PSB) on alfalfa growth under different phosphorus application levels. In this experiment, a complete randomized block design was used. The following four bacterial applications were used: inoculation of Funneliformis mosseae (Fm), inoculation of Bacillus megaterium (Bm), inoculation of mixed species (Fm × Bm) and noninoculation treatment (CK). Phosphorus (P) treatment was applied at the following four levels: 0 mg kg−1 (P0), 50 mg kg−1 (P1), 100 mg kg−1 (P2) and 150 mg P kg−1 (P3). The results showed that with the increase in phosphorus application, each index increased first and then decreased. The J2 treatment was significantly greater than the J0 treatment (P < 0.05) under the same bacterial treatment. In each cropping period the difference in each index to alfalfa was extremely significant under J, P treatment and J × P interactive treatment (P < 0.01). The indexes were compared by membership function. The priority order was as follows: J3P2 > J1P2 > J3P1 treatment. Therefore, when phosphorus was applied at 100 mg kg−1, the mixed inoculation of Fm × Bm was optimal, benefitting mycorrhiza growth and the production performance of 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 m 3 /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 P 2 treatment were significantly greater than those in the P 1 and P 3 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 (P 0 ) 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 P 0 treatment. Correlation analyses showed that total hay yield was significantly positively correlated with total phosphorus uptake and wateruse 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, W 2 P 2 > W 3 P 2 > W 1 P 2 . Therefore, an irrigation rate of 6,000 m 3 /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. K E Y W O R D Salfalfa, available phosphorus, drip irrigation, hay yield, total phosphorus, water-and phosphorus-use efficiency | 2407 ZHANG et Al.

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 N0, N1, and N2, respectively) and P (0, 50, 100, and 150 kg ha−1, referred to as P0, P1, P2, and P3, respectively) was established and resulted in the production of high‐quality alfalfa under drip irrigation. The crude protein (CP) content in the N1 treatment was greater than that in the N2 treatment under the P0, P2, and P3 treatments. Compared with that in the N1P0 and N2P3 treatments, the relative feed value (RFV) in the N1P2 treatment increased by 9−21% and 8−18%, respectively. The annual total CP yield in the N1P2 treatment was the greatest. Compared with that in the N1P3 treatment, the total PUE in the N1P2 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.

Alfalfa (Medicago sativa L.)is an important forage with high quality and fine root turnover rate (FRTR). Soil phosphorus (P) availability greatly influences dry matter yield (DMY) and persistence of alfalfa. However, the effects of water (Wa)-P coupling under drip irrigation conditions on alfalfa FRTR and DMY have been rarely studied. Therefore, a 2-yr field experiment was established with three randomized complete blocks in Xinjiang, China, evaluating three irrigation amounts (5,250, 6,000, and 6,750 m 3 ha −1 , referred to as W 1 , W 2 , and W 3 , respectively) and four P application rates (0, 50, 100, and 150 kg ha −1 , referred to as P 0 , P 1 , P 2 , and P 3 , respectively) in 2017 and 2018. The Wa-P interaction had a significant effect on alfalfa DMY (P < .05), and DMY reached the maximum at W 2 P 2 treatment. Fine root biomass (FRB) presented a bimodal pattern over time (on 21 June and 20 August) and mainly existed in the soil layers 20-40 cm underground. All root variables including FRB were positively correlated with alfalfa DMY. Comprehensive analysis showed that W 2 P 2 was the optimal treatment of the 12 treatments. Therefore, the irrigation amount of 6,000 m 3 ha −1 and P application rate of 100 kg ha −1 seems beneficial to achieve the relatively rational FRTR and the greater DMY of alfalfa. INTRODUCTIONAlfalfa (Medicago sativa L.) is a perennial high-quality legume forage (Fan et al., 2020). It is known as the "queen of forage" for its high yield, rich protein, good palatability, biological nitrogen fixation ability, and wide adaptability Abbreviations: DMY, dry matter yield; FRB, fine root biomass; FRM, fine root mortality; FRP, fine root production; FRTR, fine root turnover rate; Har, harvest; TFRB, total fine root biomass; Wa, water

Rational water and fertilizer management have an important impact on alfalfa production. This research aimed to explore the effects of water and phosphorus (P) fertilizer on hay yield, nutrient quality, water-use e ciency (WUE) and phosphorus-recovery e ciency (PRE) of each cut of alfalfa under drip irrigation and to determine the best water and P interaction model for high quality and yield of alfalfa. In this study, different irrigation levels, i.e., 5.25, 6.0, and 6.75 ML ha -1 (referred to as W 1 , W 2 , W 3 , respectively), and P fertilizer levels (0, 50, 100, and 150 kg P 2 O 5 ha -1 referred to as P 0 , P 1 , P 2 , P 3 , respectively) were set to determine the hay yield and nutrient quality of each cut of alfalfa under drip irrigation and to calculate WUE and PRE. The hay yield of each cut of alfalfa increased rst and then decreased with increased P fertilizer under the same irrigation amount, and there was no signi cant difference among different irrigation treatments with respect to the hay yield of alfalfa. The crude protein (CP) reached a maximum under the W 2 P 2 treatment. WUE decreased gradually with an increasing irrigation amount under the same P application. The WUE of alfalfa increased rst and then decreased with the increase of P application under the same irrigation amount, and WUE was 0.20%-4.75% (2016) and 1.31%-6.22% (2017) higher in the P treatments than in the non-phosphorus treatments. PRE decreased gradually with increasing P application under the same irrigation amount. Therefore, we conclude that moderate irrigation (6.0 ML ha -1 ) and P fertilizer (100 kg P 2 O 5 ha -1 ) combined with application, the alfalfa has higher WUE and PRE, and can signi cantly promote the alfalfa hay yield and nutrient quality of each cut.