Responses of agricultural soil quality and bacterial diversity and community composition to the application of combined organic-inorganic fertilizers in a watermelon production system in Northeast China

Abstract Fertilization is an important farm management measure to increase the production and quality of various crops. In this regard, application of a mixture of organic and inorganic fertilizers is usually recommended. However, effects of combined fertilizer application on soil properties and microbial communities in watermelon farmland are not clear. A large-scale field experiment with mixed inorganic–organic fertilizers was conducted in the Northeast Plain with the aim of analyzing watermelon quality, soil physicochemical properties and microbial communities in response to different fertilizer treatments. When assessing the microbial communities, OTUs were used as the smallest taxonomic unit to analyze the diversity and abundance of bacteria. The results revealed that, compared with the application of organic fertilizers alone, the combined application of organic–inorganic fertilizers significantly enhanced the production yield and brix of watermelon. The combination of organic and inorganic fertilizers significantly reduced soil water content, electrical conductivity, pH and increased soil nutrient content compared with the application of only organic fertilizers. Treatments applying 37.5 kg·hm −2 of inorganic fertilizer were more helpful in increasing the diversity as well as the abundance of soil bacteria when the same organic fertilizer was applied. Mantel test analysis showed that available phosphorus was an important environmental factor affecting the bacterial communities of soil. Our study emphasized that while applying organic fertilizers, appropriately reducing the application of inorganic fertilizers is more conducive to improving soil quality. This study provides new insights into the application of a rational mix of organic and inorganic fertilizers in the region.