Understanding increased grain yield and water use efficiency by plastic mulch from water input to harvest index for dryland maize in China’s Loess Plateau

Abstract

In China’s Loess Plateau, plastic mulch (PM) is an effective agronomic practice for dryland maize (Zea mays L.) to increase grain yield (GY) and water use efficiency (WUE) under water-limited conditions. However, there is dearth of quantitative data on how PM affects field water use step by step, subsequently increasing GY and WUE. The study aimed to identify which changes in the field water use pathway generated the positive effects of PM on GY and WUE. During the early vegetative stage (EVS), late vegetative stage (LVS), reproductive stage (RS), and entire growing season (GS), the field water use pathway was divided into five sequential steps: total water input (TWI), evapotranspiration to TWI ratio (ET/TWI), transpiration to ET ratio (T/ET), transpiration efficiency (TE), and harvest index (HI). A seven-year field experiment demonstrated that although TWI_GS exhibited no change, TWI_LVS and TWI_RS increased by 6.7 % and 5.4 %, respectively, on average following PM application. This highlighted the PM’s ability to increase water input into fields. Overall, PM negatively, neutrally, and positively affected ET/TWI_EVS (−29.8 %), ET/TWI_LVS, and ET/TWI_RS (+23.9 %), respectively, and thereby made unchanged ET/TWI_GS. There were average increases of 83.3 %, 29.8 %, 26.1 %, and 33.9 % by PM for T/ET_EVS, T/ET_LVS, T/ET_RS, and T/ET_GS respectively. Therefore, increased diversion of inputted water to T occurred in fields with PM. TE positively responded to PM during the LVS and RS. PM increased TE_LVS by 20.9 % and TE_RS by 44.1 % on average, signifying increased aboveground biomass produced per unit T under PM. The proportion of aboveground biomass partitioned to grains remained unaffected by PM as indicated by the neutral response of HI to PM. Increased water input into fields, diversion of inputted water to T, and aboveground biomass produced per unit T contributed to increased GY (+19.9 %) and WUE (+20.0 %) after applying PM. The study enhances our understanding of improved field water use pathway to produce more grains using limited water supplies in PM-based drylands in China’s Loess Plateau and similar regions worldwide.