Straw retention and plastic mulching enhance water use via synergistic regulation of water competition and compensation in wheat-maize intercropping systems

Synergistic regulation of water competition and compensation is critical for the effective use of water in sustainable intercropping systems. A field experiment was conducted on different measures of plastic mulching and straw retention (no-tillage with straw standing in wheat strip and two-year plastic mulching in maize strip, NTSSI2; no-tillage with straw covering in wheat strip and two-year plastic mulching in maize strip, NTSI2; conventional tillage with straw incorporation in wheat strip and annual new plastic mulching in maize strip, TSI; and conventional tillage without straw retention in wheat strip and annual new plastic mulching in maize strip, CTI), which were used in strip intercropping from 2014 to 2016. We determined the effects of integrated measures on coordinating water competition and compensation between inter-strips. The intercropped wheat competed for soil water from the maize strips during the wheat growth period. After wheat harvest, the intercropped maize obtained compensatory soil water from the wheat strips. The results showed that the NTSI2 treatment favorably weakened wheat competition of soil water from the maize strip and strengthened wheat strip compensation of soil water for maize growth compared with CTI treatment. Thus, compared to the CTI treatment, the potential movement amount of soil water in NTSI2 was lowest, decreased by 25.8–58.9% during wheat growth period, but it arrived at the highest, increased by 42.2–60.8% after wheat harvest. The NTSI2 treatment improved grain yield by 13.8–17.1% and enhanced WUE by 12.4–17.2% compared with CTI. The improvement in crop yield and WUE was partly attributed to the coordinated water competition between the inter-strips and the water compensation effect from the early-maturing wheat to the late-maturing maize.