In Situ Maize Residue Mulch Improves the Water Use Efficiency and Yield of the Subsequent Wheat under a Strip Inter‐Cropping System

CORE IDEAS: Irrigation and straw mulch increased yields and WUE, compared with non‐mulch, especially in dry years. Enhanced grain yield was largely influenced by changes in WUE, soil water, SPAD and dry matter. Residue retention in the fallow period conserves soil moisture, delays senescence and improves wheat production. Seasonal drought is a limiting factor for wheat (Triticum aestivum L.) production in the southwest hill regions of China. During a 4‐yr field experiment conducted in Jianyang, Sichuan Basin, we evaluated the effects of production‐system residue retention on water use, physiological characteristics, and grain yield of winter wheat grown in a relay strip cropping system. Four treatments were used: whole‐period without mulch or irrigation (NM), no mulch plus irrigation at sowing and jointing (NMI); whole‐period mulch without irrigation (WM); and fallow‐period mulch without irrigation (FM). The results were that irrigation and straw mulch increased yields by 0 to ∼42% and water use efficiency (WUE) by 0 to ∼30%, compared with NM, especially in dry years. Improvement in grain yield under residue retention was attributed to increased spike number. Residue retention significantly improved the following crop parameters; tiller numbers, aboveground dry mass accumulation, soil moisture, root length density, and root surface area at critical growth stages, as well as inhibiting leaf chlorophyll loss after anthesis. The FM achieved greater performance on the above parameters than WM. Enhanced grain yield was largely influenced by changes in WUE, gravimetric soil water, SPAD value and dry matter accumulation. In conclusion, residue retention over the fallow period is instrumental in conserving soil moisture, delaying leaf senescence and improving wheat production. This treatment was also the most convenient for farmers.