Objectives We compared the effects of planting different grass species in peach orchards on the soil physicochemical properties and microbial community structures, so as to provide technical support for the sustainable development of orchard soil.

Methods A field experiment was conducted at Yuanwang Peach Orchard Experimental Base, Jiande City, Zhejiang Province. Four grass species, milk vetch (Astragalus sinicus), white clover (Trifolium repens), rat grass (Vulpia myuros), and vetch (Vicia sativa), were sowed on inter-row of peach trees in October 2019, and clear tillage was used as control. In April (full blooming stage) and July (peach maturing stage) of 2022, soil was sampled for the determination of pH, organic matter and available N, P, K contents. At peach harvest of 2022, the weed species in each treatment were investigated, the soil microbial community structure, and fruit yield and appearance quality were measured.

Results Grass cultivation significantly reduced the number of weeds, with the weed species number of 9, 10, 11, 6, and 18 in plots of milk vetch, white clover, rat grass, vetch, and the control. Compared with control, grass treatments increased soil available N, P, K, and organic matter content, with the highest increment observed in rat grass treatment. Milk vetch was recorded higher alpha diversity indices of bacteria than control, white clover, rat grass and vetch treatment were recorded lower values (P<0.05). In addition, the number of unique OTUs of soil bacteria under milk vetch treatments were higher than that of the other grass treatments and control, which was favorable for the propagation of soil bacteria in peach orchard. PCoA analysis showed that the soil fungi community in the milk vetch treatment plots differed less between and within groups than those in the control plot. White clover treatment significantly increased the percentage of Acidobacteria sequences; and at the fungi phylum classification level, the milk vetch and rat grass treatments significantly increased the percentage of Ascomycota sequences. Rat grass treatment resulted in a larger fruit transverse diameter, higher sugar content, and higher yield per plant. Correlation analysis showed that the relevant abundance of a large number of bacterial phyla were positively correlated with soil nutrient levels and pH. Specifically, there was a positive correlation between Elusimicrobia, Nitrospirae, Dependiae, Latescibacteria, and Fibrobacteres and soil physicochemical properties. PCA (principal component analysis) further showed that rat grass and white clover treatments had greater effects on fruit quality, yield per plant, and soil physicochemical properties.

Conclusions Continuous three-year cultivation of grasses improved soil available nutrients and organic matter in peach orchard soils significantly, decreased the number of weed species to different extent. Negative grass Vicia sativa did not change soil microbial structure but declined their diversities. Rat grass and milk vetch enhanced soil microbial richness, with rat grass being more effective in enhancing soil nutrients, resulting in significant improvements in fruit quality.