Effects of ridge tillage and mulching on water availability, grain yield, and water use efficiency in rain-fed winter wheat under different rainfall and nitrogen conditions

Tillage practices which improve water availability and water use efficiency (WUE) are beneficial for rain-fed agriculture. However, there is little consensus about the effects of ridge tillage and mulching, combined with different rainfall and N fertilization conditions, on water status and productivity in winter wheat fields. The current study aimed to investigate the effects of ridge tillage and mulching on water availability, grain yield, and WUE in rain-fed winter wheat under different rainfall and N conditions. A three-year field experiment was conducted during 2011-2014 following a split-split plot design. The experiment included two humid growing seasons (2011-2012 and 2013-2014) and one dry growing season (2012-2013). Nitrogen application rates were 0 and 180 kg N ha(-1). Tillage systems included conventional tillage (CT, as control), stalk mulching (SM), film mulching (FM), ridge tillage without mulch (RT), ridge tillage with film on ridges (RTf), and ridge tillage with film on ridges and stalk in furrows (RTfs). Results showed that averaged across growing seasons and N treatments, ridge tillage and mulching decreased evapotranspiration by 8.3%-16.2%, and increased grain yield and WUE by 4.2%-15.2% and 16.7%-36.8% compared with CT, respectively. Ridge tillage and mulching tended to increase grain yield especially when rainfall was deficient, and tended to increase WUE especially when N supply was deficient. Spike number per hectare and grain number per spike made significant contributions to grain yield when all three yield components were considered. Ridge tillage and mulching tended to increase mass based and area-based canopy moisture during regreening (stage 6 in Feekes scale, late Feb-early Mar) to grain filling stage (middle May) which was positively correlated with grain yield. Lower leaf area index (LAI) in ridge tillage and mulching treatments led to grain yield loss, but the loss was alleviated by greater total chlorophyll in flag leaves. Overall, ridge tillage and mulching improved water availability, grain yield, and WUE in rain-fed winter wheat, especially when N and rainfall were deficient.