Response Mechanism Ofwinter Wheat Yield And Water Use Efficiency To The Change Of Rainfall In The Loess Tableland

A typical climatic feature of the Loess Plateau is the large variation in the annual and interannual precipitation.Winter wheat is the main crop in the Loess Plateau area,but its growth period is not synchronized with the precipitation and the precipitation in the growing season is sparse.As a result,soil water storage becomes an important source of water for winter wheat growth.Investigating the responses of winter wheat yield and water use efficiency?WUE?and their relationships with soil water under rainfall changes,quantifying the source of winter wheat water use are of great significance for the management of dryland farmland water management and the stability of winter wheat yield.In this paper,three precipitation gradients are simulated using artificial shelters and gravity drip irrigation systems in field observations:normal precipitation?Rc?,a decrease of 1/3 precipitation?R^-?and an increase of 1/3 precipitation?R⁺?.The impact of precipitation changes on soil water,winter wheat yield,and WUE for 2014-2017was combined with stable isotope hydrogen and oxygen isotope tracer technique to identify the source of wheat water use.The following conclusions were reached:?1?Changes in rainfall significantly affect soil water storage.The 0-300 cm soil water storage gradually decreased during the winter wheat growing season and recovered in the rainy season.Soil water storage at depths of 0-380 cm decreased by 167.1 mm and 216.4 mm,respectively,for Rc and R-treatments.Soil water storage at depths of 0-300 cm for R+treatment decreased by 31.5 mm,and soil water at a depth of 300-380 cm increased by 32.8 mm.Soil water storage is positively correlated with rainfall amount.?2?Soil water and precipitation both affect the biomass and yield of winter wheat.When the soil water before sowing is sufficient,even if the growing season rainfall amount is reduced,the winter wheat yield and biomass have little difference compared with the normal rainfall treatment?2014-2015?;when the soil water before sowing is insufficient and the growth period is less,the winter wheat yield will be seriously reduced by around 50%?2015-2016?;When the soil water before sowing is insufficient,even if the growing seaon rainfall amount is large,the winter wheat yield will have a certain degree of reduction?2015-2016?.The relationship between grain yield and rainfall during the growth period and the soil water before sowing showed a saturation effect.?3?Changes in rainfall significantly affected the WUE of winter wheat.In 2014–2015,the WUE for R⁺treatment was reduced by 1.9 kg ha^-1mm^-1?15.7%?compared to Rc,but for R^-treatment,the WUE was increased by 0.9 kg ha^-1mm^-1?0.7%?.In 2015-2016,compared to Rc,the WUEs for R⁺and R^-treatments were reduced by 4.7 kg ha^-1mm^-1?30.5%?and 4.7 kg ha^-1mm^-1?30.9%?,respectively.In 2016-2017,the WUEs of R⁺and R^-treatments increased by1.3 kg ha^-1mm^-1?12.3%?and 4.8 kg ha^-1mm^-1?45.3%?,respectively compared to Rc.The WUE of winter wheat shows a“single-peak curve”relationship with rainfall amount and soil water during the growth period.?4?Winter wheat mainly utilizes 0-20 cm soil water.Its contribution rates are 71.8%for the jointing period,63.3%for the heading to anthesis,46.8%for the grain filling period,and53.3%for the milk ripening period to maturity.The contribution of 20-60 cm soil water reached its maximum?44.7%?during grain filling.Under the condition of increasing rainfall,winter wheat mainly uses shallow soil water?0-60cm?,but it still has a certain degree of utilization for deep soil water?60-300cm?;reduced rainfall promotes winter wheat to use deeper soil water.The distribution of winter wheat roots and soil water storage are the main factors determining the water use of winter wheat.In this study,we found that the soil water before sowing and rainfall at the growth stage play an essential role in maintaining the stability of winter wheat yield.Although the change of rainfall modified the utilization strategy of winter wheat to different depth soil water,the surface soil water is still the primary source of water use of winter wheat.Therefore,it is effective to adopt agricultural measures to increase soil water storage during summer and growing seasons for ensuring the stability of winter wheat yield in loess tableland region.