Responses of soil microorganisms, enzyme activities and nutrient contents to inter-row grass ploughing and returning to the field in a natural sod culture apple orchard

Natural sod culture in orchard is an effective measure to improve the orchard productivity and promote the sustainable production. To explore the effects of inter-row grass ploughing and returning on soil biological cha-racteristics and nutrient contents, we examined the effects of different grass returning to the field on the amount of soil microorganisms, enzyme activities and nitrogen and potassium contents of 0-20 cm soil layer. There are three treatments, cleaning tillage as the control (CK), conventional mowing management (NG), and soil ploughing annually under natural sod culture with conventional mowing condition (NGR) treatments. The results showed that soil microorganisms were dominated by bacteria, followed by actinomycetes, with the least fungi. Compared with CK, both NG and NGR treatments significantly improved the abundance of soil bacteria and fungi, with the strongest effects in NGR treatment, and significantly increased the soil urease, sucrase and catalase activities by 59.0%, 20.7%, 38.3% and 73.5%, 45.9%, 67.8%, respectively. NGR treatment significantly increased soil nitrogen and potassium contents, with the contents of ammonium nitrogen, nitrate nitrogen, particulate organic nitrogen, microbial biomass nitrogen, available potassium and water-soluble potassium being 1.5, 1.8, 1.6, 2.0, 1.3 and 1.4 times of that in CK, respectively. NGR significantly increased soluble sugar content and sugar acid ratio and subsequently improved fruit quality. Overall, NGR increased soil microbial abundance, enzyme activities, nitrogen, potassium contents and fruit quality, which could be a feasible management of inter-row grasses in the natural sod culture apple orchard.