Effects of Phosphate Solubilizing Bacteria and Arbuscular Mycorrhizal Fungi on the Production of Alfalfa under Phosphorus Fertigation

Alfalfa (Medicago sativa L.) is an important forage legume in semiarid areas of China. Comprehensive studies on the growth, nutritional quality and underground biomass of alfalfa under water-phosphorus coupling with the simultaneous inoculation of phosphate-solubilizing bacteria (PSB) and arbuscular mycorrhizal fungi (AMF) are scarce. An orthogonal experimental design [L16 (4(3))] was used and the soil water holding capacity, phosphorus (P) application rate and bacterial inoculation treatments each had 4 levels. The four water holding capacities were 35% (W-1), 50% (W-2), 65% (W-3), and 80% (W-4). The four P rates were 0 mg.kg(-1) (P-0), 50 mg kg(-1) (P-1), 100 mg kg(-1) (P-2) and 150 mg kg(-1) (P-3). The four inoculation treatments were no inoculation (J(0)), Bacillus megaterium (J(1)), Funneliformis mosseae (J(2)) and double inoculation (B. megaterium + F. mosseae) (J(3)). The results showed that the dry matter yield, plant height and stem diameter in all treatments were significantly higher than those in the CK treatment (P <= 0.05), and were the highest under the W(3)P(2)J(0) treatment. At the same water holding capacity, the taproot length and underground biomass in the J(0) treatment were significantly greater than those in the J(1), J(2) and J(3) treatments (P <= 0.05). The soil pH values in the J o treatment were significantly lower than those in th J(1), J(2) and J(3) treatments (P <= 0.05). The aboveground biomass, plant height, crude protein, neutral detergent fibre, acid detergent fibre, taproot length and underground biomass were influenced by factors in the order of water > P > bacteria, and these factors affected the stem diameter and P concentration of the alfalfa from most to least as P > water > bacteria. The dry matter yield of alfalfa was positively correlated with the plant height, taproot length and underground biomass (P <= 0.01) and was negatively correlated with the neutral detergent fibre and acid detergent fibre contents (P <= 0.05). The four treatments that had the greatest influence on the production performance of alfalfa were W(3)P(1)J(3) > W(3)P(2)J(0) >W(3)P(3)J(1) > W(3)P(0)J(2). We concluded that a soil water capacity of 65%, a P application rate of 44.6 mg kg(-1), and inoculation with AMF and PSB were the most effective conditions for promoting alfalfa growth. (C) 2020 Friends Science Publishers