Soil water balance dynamics under plastic mulching in dryland rainfed agroecosystem across the Loess Plateau

In rain-fed semiarid areas, low soil water availability is a major challenge constraining crop productivity and agricultural sustainability. Soil surface mulching with plastic film has been widely used to improve soil water availability in the Loess Plateau of China. However, a systematic assessment on soil water balance dynamics under plastic mulching is still lacking. We conducted a meta-analysis on plastic mulching observations across the Loess Plateau to quantify the intensity of evapotranspiration (ET), spatiotemporal dynamics of soil water storage (SWS), and annual soil water balance in the plastic mulching systems. The results indicated that compared with non-mulching, plastic mulching significantly enhanced ET by 2.6% across the entire dataset. The magnitude of intensified ET was strongly associated with mulching pattern, mean annual precipitation and nitrogen application. Plastic mulching led to a significant increase in SWS by 8.4% at 0−60 cm soil layer, yet a decrease by 0.8% at 60−200 cm layer over the growing season, comparing with non-mulching. Importantly, an effective water recovery effect was observed at the deep soil layer under plastic mulching, as evidenced by the significantly greater SWS (+30%) over the fallow season, in comparison with that of non-mulching. Nitrogen input level and mean annual precipitation proved to be the most important factors in driving SWS. As a result, crop yield and water use efficiency were substantially improved under plastic mulching, and such enhancements were the most pronounced under full plastic mulching and lower annual mean precipitation. Increased vegetation growth due to plastic mulching can turn to impact soil water dynamics in both growing and fallow seasons, but it did not disrupt the annual equilibrium of SWS. Particularly, more precipitation storage at deep soil layer during the non-growing season appeared to fully offset the extra water loss by enhanced ET. Our findings provide critical insight into the success of plastic mulching farming practice regarding field productivity and soil water sustainability.