Optimizing Phosphorus Application Rate and the Mixed Inoculation of Arbuscular Mycorrhizal Fungi and Phosphate-solubilizing Bacteria Can Improve the Phosphatase Activity and Organic Acid Content in Alfalfa Soil

Abstract Alfalfa (Medicago sativa L.) is an important high-quality legume forage, and phosphorus is an important nutrient element for high-quality and high-yield of alfalfa. This study assessed the effects bacteria and phosphorus (P) use efficiency of alfalfa soil under different P applications. In this experiment, a two-factor complete randomized block design was used. Four bacterial treatments were as follows: Funneliformis mosseae (Fm), Bacillus megaterium (Bm), double inoculation (Fm × Bm) and no inoculation bacteria (CK). There are four levels of phosphorus treatment, namely: phosphorus application 0 (P0), 50 (P1), 100 (P2), 150 mgžkg-1 (P3). There were 16 treatments in total, and each treatment was repeated 6 times. The results showed that the effects of single inoculation and mixed inoculation were significantly higher than those of noninoculation (P < 0.05). With the increase in phosphorus application, each index increased first and then decreased. The alkaline phosphatase activity (AKP) and organic matter (SOM) content in soi lincreased with the increase of cutting times, and the content of organic matter in rhizosphere soil was higher than that in non-rhizosphere soil. Principal component analysis (PCA) shows that the top three treatments were J3P2 > J3P1 > J3P3. Therefore, when (P2O5) was 100 mgžkg-1, the mixed inoculation of Fm × Bm could improve the phosphatase activity in alfalfa soil, promote the secretion of organic acids in rhizosphere soil and then improve the content of soil fertility.