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 legume forage, and phosphorus is a significant nutrient element of alfalfa with high quality and high yield. However, the effect mechanism of different phosphorus application rates on soil bacteria, and the phosphorus efficiency of alfalfa are still unclear. Therefore, we present the results of a study in which alfalfa was inoculated with Funneliformis mosseae, Bacillus megaterium, double inoculated with Funneliformis mosseae and Bacillus megaterium, and given no inoculation bacteria. P₂O₅ was applied under the condition of bacterial inoculation, and the contents were 0, 50, 100, and 150 mg kg⁻¹, respectively, to explore the effect of bacterial inoculation on alkaline phosphatase, organic acid, pH, organic matter, and the relationship between the indicators in alfalfa soil, under different phosphorus application rates. The effect of mixed inoculation was significantly higher than that of the non-inoculated control group (p < 0.05). The organic matter content of rhizosphere soil was higher than that of non-rhizosphere soil. When the phosphorus application rate was 100 mg kg⁻¹, the content of alkaline phosphatase in the soil inoculated with Funneliformis mosseae and Bacillus megaterium was better than that in the single inoculation, and no inoculation. Principal component analysis showed that the top three treatments were: double inoculation bacteria and treatment group with phosphorus application rate of 100 mg kg⁻¹ >; double inoculation bacteria and treatment group with phosphorus application rate of 50 mg kg⁻¹ >; double inoculation bacteria and treatment group with phosphorus application rate of 150 mg kg⁻¹. In addition, when P₂O₅ was 100 mg kg⁻¹, the addition of Funneliformis mosseae and Bacillus megaterium to alfalfa soil could increase the content of organic matter in the soil, promote the metabolism of alfalfa root exudates, and increase the organic acid of the rhizosphere soil, compared with the control without inoculation, and without phosphorus application. At the same time, the phosphatase activity in the soil had a significant positive correlation with malic acid, oxalic acid, acetic acid, total organic acid, and soil pH, thereby improving soil fertility and promoting phosphorus absorption by plants. These findings provide new insights into alfalfa root soils and the effects of Funneliformis mosseae and Bacillus megaterium additions on soil nutrients.

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.

The present study aimed to investigate the nitrogen (N) and phosphorus (P) fertilization of continuous addition effects plant biomass, the physiological properties of leaves and the antioxi-dant enzyme activities of alfalfa (Medicago sativa L) in the northern Xinjiang region; including the no fertilization (CK), nitrogen fertilization (N, 120 kg·ha⁻¹), phosphorus fertilization (with low amount of N) (P, 100 kg·ha⁻¹ P and 23.5 kg·ha⁻¹ N) and combined nitrogen and phosphorus fertilization (NP, 120 kg·ha⁻¹ N and 100 kg·ha⁻¹ P) on the K well supplied soil. After three consecutive years of the supply of N and P fertilization, samples were taken at the first flowering of alfalfa (four clippings in the total year) to determine its pigment concentration, stomatal aperture, antioxidant enzyme activity and hay yield. The results showed that NP fertilization promoted growth with a higher number of branches and hay yield of alfalfa, while N or P fertilization alone had a positive effect on the growth of alfalfa. However, P fertilization significantly increased the carotenoid (Car) content at the early flowering stage of alfalfa leaves (during four clippings) (p < 0.05), In addition, NP ferti-lization enhanced stomatal aperture, increased the antioxidant enzyme activity and decreased the oxidized substance at the early flowering stage of alfalfa leaves. The results showed that a N and P balance rather than an absolute amount of either enhanced the growth of alfalfa, and N or P fertili-zation affects physiological traits differently. We propose that NP fertilization increases the nutri-tional characteristics and physiological characteristics, enhancing the adaptive capacity of alfalfa and making it better adapted to external environmental changes.

Soil organic carbon (SOC) is the principal factor contributing to enhanced soil fertility and also functions as the major carbon sink within terrestrial ecosystems. Applying fertilizer is a crucial agricultural practice that enhances SOC and promotes crop yields. Nevertheless, the response of SOC, active organic carbon fraction and hay yield to nitrogen and phosphorus application is still unclear. The objective of this study was to investigate the impact of nitrogen-phosphorus interactions on SOC, active organic carbon fractions and hay yield in alfalfa fields. A two-factor randomized group design was employed in this study, with two nitrogen levels of 0 kg·ha^-1 (N₀) and 120 kg·ha^-1 (N₁) and four phosphorus levels of 0 kg·ha^-1 (P₀), 50 kg·ha^-1 (P₁), 100 kg·ha^-1 (P₂) and 150 kg·ha^-1 (P₃). The results showed that the nitrogen and phosphorus treatments increased SOC, easily oxidized organic carbon (EOC), dissolved organic carbon (DOC), particulate organic carbon (POC), microbial biomass carbon (MBC) and hay yield in alfalfa fields, and increased with the duration of fertilizer application, reaching a maximum under N₁P₂ or N₁P₃ treatments. The increases in SOC, EOC, DOC, POC, MBC content and hay yield in the 0–60 cm soil layer of the alfalfa field were 9.11%-21.85%, 1.07%-25.01%, 6.94%-22.03%, 10.36%-44.15%, 26.46%-62.61% and 5.51%-23.25% for the nitrogen and phosphorus treatments, respectively. The vertical distribution of SOC, EOC, DOC and POC contents under all nitrogen and phosphorus treatments was highest in the 0–20 cm soil layer and tended to decrease with increasing depth of the soil layer. The MBC content was highest in the 10–30 cm soil layer. DOC/SOC, MBC/SOC (excluding N₀P₁ treatment) and POC/SOC were all higher in the 0–40 cm soil layer of the alfalfa field compared to the N₀P₀ treatment, indicating that the nitrogen and phosphorus treatments effectively improved soil fertility, while EOC/SOC and DOC/SOC were both lower in the 40–60 cm soil layer than in the N₀P₀ treatment, indicating that the nitrogen and phosphorus treatments improved soil carbon sequestration potential. The soil layer between 0-30 cm exhibited the highest sensitivity index for MBC, whereas the soil layer between 30-60 cm had the highest sensitivity index for POC. This suggests that the indication for changes in SOC due to nitrogen and phosphorus treatment shifted from MBC to POC as the soil depth increased. Meanwhile, except the 20–30 cm layer of soil in the N₀P₁ treatment and the 20–50 cm layer in the N₁P₀ treatment, all fertilizers enhanced the soil Carbon management index (CMI) to varying degrees. Structural equation modeling shows that nitrogen and phosphorus indirectly affect SOC content by changing the content of the active organic carbon fraction, and that SOC is primarily impacted by POC and MBC. The comprehensive assessment indicated that the N₁P₂ treatment was the optimal fertilizer application pattern. In summary, the nitrogen and phosphorus treatments improved soil fertility in the 0–40 cm soil layer and soil carbon sequestration potential in the 40–60 cm soil layer of alfalfa fields. In agroecosystems, a recommended application rate of 120 kg·ha^-1 for nitrogen and 100 kg·ha^-1 for phosphorus is the most effective in increasing SOC content, soil carbon pool potential and alfalfa hay yield.