Plastic mulching reduces surface-soil microbial biomass carbon and structural stability in a pear orchard

Abstract

Background and aims Plastic mulching (PM) can improve soil aggregate stability and microbial activity, thereby preventing soil degradation in crop fields, which are different from the conditions in the orchard. However, little is known about the response of surface-soil microbial and structural stability to PM applied in orchards. Methods An experiment was conducted from 2017 to 2020 in a pear orchard. Two treatments consisted of no mulching and plastic (black woven polypropylene fabric) lying under a pear tree canopy. Results Results showed that the soil microbial biomass carbon content (MBC), organic carbon content (SOC), and ratio of MBC/SOC of PM treatment declined by 49.2%, 13.4%, and 41.3%, respectively. In particular, the significant decline in ratio of MBC/SOC indicated that SOC content would decrease in the future. Mean weight diameter and geometric diameter of soil aggregates in PM treatment decreased by approximately 20%, as compared with no mulching. The decrease in MBC, SOC and soil aggregates stability under PM were mainly resulted from the reduction in root exudate production and root-associated symbionts, causing by the absence of grass roots. These can be proved by the soil gas exchange and concentration. Soil respiration and mineralization were decreased by PM, but soil oxygen concentration at 10 cm depth in PM were improved, due to the oxygen consumed by microbial in no mulching treatment and low gas exchange at this depth. Conclusions Unlike the crop field, protecting the surface soil in orchard from degradation under long-term plastic mulching application is worth considering.