Effects of tillage and seasonal variation of rainfall on soil water content and root growth distribution of winter wheat under rainfed conditions of the Loess Plateau, China

Drought is the leading cause of low and unstable wheat yield in dryland. The field experiment was performed from 2009 to 2017 in the eastern part of Loess Plateau, China, to study the effect of tillage (deep ploughing, DP and no-tillage, NT) and seasonal variation in precipitation on soil moisture and root traits and grain yield of wheat. In dry seasons, soil water content, root length surface density (RLSD), and root diameter peaked at 60 cm depth, but in the normal/wet seasons, peaked at 40 cm depth. The reduction of RLSD at anthesis by drought was 44% under NT and 29% with DP, while the reduction in above-ground dry weight was 67% under NT and 56% under DP. More soil water was depleted from the deep soil layer (80-100 cm depth) than that in the shallow layer (20-60 cm depth) from jointing in the dry seasons, and from anthesis in the normal/wet seasons. The higher amount of effective in-seasonal rainfall in the dry seasons increased RLSD at anthesis by 44% with NT and 21% with DP and increased grain yield by 24.1% under NT and 14.2% under DP. The average grain yield in the dry seasons was 28-41% lower than in the normal/wet seasons. The average water use efficiency (WUE) in the dry seasons was 42-54% lower than that in the normal/wet seasons. WUE with DP was 32% higher than that with NT in the dry seasons, while it was 15% higher than that with NT in the normal/wet seasons. The average contribution rates of soil water content at sowing to grain yield under DP and NT were 23-25% in the dry seasons, and 52-53% in the normal/wet seasons. Thus, deep ploughing in summer fallow should be adopted for high water storage and yield stability.