Organic fertilizer and hydrothermal conditions change the distribution of Medicago sativa L. productivity and soil bacterial diversity in coastal saline soil

Abstract Background Alfalfa (Medicago sativa L.) is a perennial leguminous forage that can improve the properties of saline soil. In addition, the supplementation with fertilizer to promote soil bacterial activity is critical to improve the productivity of coastal saline soils. However, the association between fertilizer application, bacterial community characteristics, and alfalfa yield in saline soil remains unclear. Aim To understand the interaction of different fertilizer and environmental factors on soil bacterial diversity and alfalfa yield in coastal saline soil. Results A 4-year field study was conducted to examine the interaction of different fertilizer treatments and environmental factors on soil bacterial diversity and alfalfa yield in coastal saline soil in China. Three organic fertilizer treatments (fulvic acid potassium, fulvic acid potassium + wood vinegar, and fulvic acid potassium + Bacillus), one biochar treatment (bio-charcoal), one inorganic fertilizer treatment (diammonium phosphate), and a control (no fertilizer) were included. The effects of the six treatments and 15 cutting times on alfalfa yield and soil bacterial community diversity were assessed. The productivity in fulvic acid potassium + Bacillus and fulvic acid potassium treatments was 68.37 and 67.90 t·hm−2 in 4 years, which was significantly higher than that in the bio-charcoal treatment and control. Hydrothermal conditions and timing of alfalfa harvest had significant effects on the soil bacterial community. Proteobacteria, Acidobacteria, and Actinobacteria were the principal bacterial phyla detected in the soil samples, collectively accounting for approximately 60% of the total bacterial abundance. The relative abundance of Bacteroidetes, Firmicutes, and Nitrospirae was significantly correlated with alfalfa yield, and the abundance of these phyla was also affected by the maximum temperature and precipitation. Fertilizer supplementation in coastal saline soil can effectively increase the yield of alfalfa. Among the fertilizers tested, fulvic acid potassium had the strongest effect, whereas bio-charcoal fertilizer had little effect on alfalfa yield. Graphical Abstract