Soil water storage, winter wheat yield, and water-use efficiency with cover crops and nitrogen fertilization

Summer cover crops extract soil water and may affect succeeding winter wheat (Triticum aestivum L.) yield and water-use efficiency (WUE). We examined the effect of summer cover crops and N fertilization rates on soil water storage at wheat planting (SWP) and harvest (SWH), winter wheat yield, evapotranspiration (ET), and WUE from 2017-2018 to 2019-2020 at Changwu and Chang'an in the Loess Plateau of China. Cover crops were soybean [Glycine max (L.) Merr., SB], sudangrass [Sorghum sudanense (Piper) Stapf, SG], soybean and sudangrass mixture (SS), and no cover crop (CK) and N fertilization rates were 0, 60, and 120 kg N ha(-1) applied to winter wheat. Soil water was measured to a depth of 2 m at wheat planting and harvest, and grain yield, ET, and WUE of wheat were evaluated. Cover crop biomass was greater for SS than SB at both sites. The SWP and ET were greater for CK than other cover crops at all N fertilization rates, but SWH varied for cover crops, N fertilization rates, years, and sites. Winter wheat grain yield and WUE were greater for SS than other cover crops and increased with increased N fertilization rates in all years and sites. Although SS and 120 kg N ha(-1) reduced SWP and ET, wheat yield and WUE were greater than other cover crops and N fertilization rates in the semiarid climatic condition of the Loess Plateau of China where annual precipitation is adequate to reduce the detrimental effect of water stress.