Residual plastic film decreases crop yield and water use efficiency through direct negative effects on soil...

Film mulching has been extensively used to improve agricultural production in arid regions of China. However, without sufficient mulch film recovery, large amounts of residual film accumulated in the farmland, which would affect crop yield and water use efficiency (WUE). In order to comprehensively analyze the effects of residual film on crop yield and WUE, and clarify its influencing mechanism, present study adopted a meta-analysis to systematically evaluate the impacts of residual film on soil physicochemical properties, crop root growth, yield, and WUE. The results showed that residual film significantly increased soil bulk density and the soil moisture content in 0-20 cm soil layer, but decreased soil porosity, soil organic matter, soil total nitrogen content, and soil moisture content in >20 cm soil layer, especially when residual film amount was >400 kg ha^-1. Residual film significantly reduced crop root dry weight, root length, root diameter, root volume and root surface area. Generally, crop yield and WUE decreased with the increase of residual film amount; and crop yield was reduced by about 14.00 % when the residual film amount increased by 1000 kg ha^-1. In average, crop yield and WUE under film residual condition were significantly decreased by 13.46 % and 9.21 %, respectively. The negative effects of residual film on root growth, yield and WUE were greater for cash crops (cotton, tomato and potato) than for cereal crops (wheat, maize). The structural equation model indicated that residual film generated indirect negative effects on crop yield and WUE by directly affecting soil physicochemical properties and crop root growth, with the standard path coefficients of -0.302 and - 0.217, respectively. The results would provide a theoretical basis for reducing residual film pollution on farmland and promoting the green and sustainable development of agriculture.