Effects of Grass Inter-Planting on Soil Nutrients, Enzyme Activity, and Bacterial Community Diversity in an Apple Orchard

The orchard inter-planting pattern is being widely used in many countries of the world, but it is relatively new in China. This study evaluated the interrow mono- and mixed-planting of Lolium perenne (Lp) and Medicago sativa (Ms) in orchards on soil nutrient, enzyme activity, and bacterial community diversity in 0–10, 10–20, and 20–40 cm soil layers. The clean tillage orchard was used as control (CK) treatment. Compared with CK, Lp and Lp + Ms. significantly increased the contents of soil organic matter (OM), total nitrogen (TN), and alkali-hydrolyzable nitrogen (AN) in 0–20-cm soil layer, and up-regulated the activities of urease (URE) and alkaline phosphatase (ALP). The Lp treatment significantly increased the relative abundance of Gemmatimonadetes and Planctomycetes in the 0-10-cm soil layer. Besides, cover crops significantly increased the abundance of Actinobacteria, Gemmatimonadetes, and Chloroflexi in the 10–20-cm soil layer and that of Gemmatimonadetes and Chloroflexi in the 20–40 cm soil layer. The redundancy analysis (RDA) showed significant positive correlations of Actinobacteria with ALP, OM and TN and that of Bacteroidetes with available potassium (AK), and Proteobacteria with available phosphorus (AP). Overall, the grass inter-planting improved the soil nutrients, enzymes activities, and bacterial community composition of the soil. Based on these results, inter-planting perennial ryegrass in the apple orchards is a suitable grass-orchard inter-planting strategy in Weibei, Shaanxi Province of China.