Soil microplastics at different depths before and after mechanical harvesting: case study in Anhui Province, China

Although mechanical harvesting has substantially increased the efficiency of agricultural production, the manner in which it influences the abundance and distribution pattern of microplastics (MPs) in the soil remains unknown. Specially, the relationships between MPs and soil physicochemical properties are unclear. Herein, soil samples before and after mechanical harvesting in Anhui Province are collected and segmented into three layers: top (0-10 cm), middle (10-20 cm), and bottom (20-30 cm). Besides analyzing MPs, standardized tests are conducted on the soil porosity, organic carbon, total nitrogen, and moisture content. Results demonstrate that the mechanical harvesting decreases the abundance of soil MPs in the top and middle layers but increases that in bottom layer. However, a considerable positive correlation between soil MP levels before and after harvesting is identified; their distribution characteristics were compared as well. We suppose that mechanical harvesting introduces a small amount of additional MPs while facilitating the penetration capacity of existing MPs. Although the soil organic carbon, total nitrogen, and moisture content are observed to positively correlate with each other, they are not directly related to MPs. Furthermore, we assume that mechanical harvesting physically drives the connection of soil porosity with other parameters, as their positive correlations become evident after harvesting. This study provides a valuable finding: MP penetration can be facilitated by mechanical harvesting, which should be considered for the prevention of potential MP-induced ecological risks on deep soil and groundwater.