Effects Of Plastic Film Mulching On Winter Wheat Yield And Water Use Efficiency And Nitrogen Use Efficiency Under Different Pre-sowing Soil Moisture Levels

The Loess Plateau is an important dryland farming area in China,water shortage is the main factor limiting the agricultural production in this region.Plastic mulching has the good effect on soil moisture conservation and can significantly improve the yield of dryland wheat.The soil moisture before sowing is the main water source for dryland wheat as precipitation during growing period.Previous studies mainly discussed the influence of film mulching on soil water and temperature,crop yield,water use efficiency and nitrogen use efficiency,but few reports on how does the interaction between soil moisture before sowing and mulching effects on wheat yield,water use efficiency and nitrogen use efficiency.The objective of this study was to investigate the effects of soil moisture before sowing and plastic mulching on wheat grain yield,water use efficiency and nitrogen use efficiency based on the 2-year field positioning experiment.The experiment involved three pre-sowing soil water levels:high pre-sowing soil water（W1）,medium pre-sowing soil water（W2）,low pre-sowing soil water（W3）,and two mulching levels:conventional tillage（C）and plastic film mulching（M）,six treatments in total.The obtained main results and conclusions were as follows:（1）The winter wheat yield ranged from 4490 to 8813 kg ha^-1,the plastic mulching significantly increased grain yield by 11.0%.Year,soil moisture before sowing and mulching had significant interactions on yield.In the average year（2019～2020）,plastic mulching had no significant effect on yield under high pre-sowing soil water level,while it significantly increased yield by 20.9%and 25.0%under the medium and low pre-sowing soil water levels,respectively.In the wet year（2020～2021）,plastic mulching significantly increased yield by6.1%under high pre-sowing soil water level,but it tended to increase yield under medium and low pre-sowing soil water levels.The harvest index ranged from 40.7%to 48.3%,mulching did not significantly affect the harvest index,soil moisture and mulching had a significant interaction effect on the harvest index.For example,mulching significantly reduced the harvest index by 4.2%and 4.4%under the high soil moisture level in 2 years,respectively,while it increased by 0.9%and 9.6%,respectively under the medium soil moisture,and had no significant effect under the low soil moisture level.（2）The range of evapotranspiration in the growth period of winter wheat was 341.1～444.4 mm.Mulching significantly reduced total evapotranspiration by 3.6%,the pre-anthesis evapotranspiration by 15.7 mm and had no significant effect on the post-anthesis evapotranspiration.The interaction between soil moisture levels and mulching had no significant effect on the total and pre or post-anthesis evapotranspiration.The water use efficiency ranged from 12.8 to 22.2 kg ha^-1 mm^-1.Under the levels of high,medium and low soil moisture,the water use efficiency increased by 0.9%～27.6%,but had no obvious response to the interaction of soil moisture and mulching.（3）The grain nitrogen uptake of winter wheat ranged from 108.0 to 179.1 kg ha^-1 and the grain nitrogen uptake under plastic film mulching significantly increased by 14.1%.The variation of aboveground nitrogen uptake ranged from 133.4～212.8 kg ha^-1,and plastic mulching significantly increased the aboveground nitrogen uptake by 12.0%.The interaction of pre-sowing soil moisture and plastic mulching had no significant effects on both grain and aboveground nitrogen uptake.The nitrogen requirement for producing 100 kg of grain ranged from 1.9 to 3.0 kg.Mulching and the interaction of mulching and pre-sowing soil moisture had no significant effects on the nitrogen requirement for producing 100 kg of yield.（4）The nitrogen partial factor productivity was 41.6～65.3 kg kg^-1,it was significantly increased by 10.9%under mulching.Nitrogen uptake efficiency（balance method）changed from 1.0～1.6 kg kg^-1,plastic mulching significantly increased by 17.7%.The nitrogen use efficiency ranged from 33.9 to 53.5 kg kg^-1,nitrogen harvest index varied from 79.6%to89.1%.Plastic film mulching had no significant effect on both nitrogen use efficiency and nitrogen harvest index.The interaction of pre-sowing soil moisture and film mulching only had significant effects on nitrogen partial factor productivity.In the average year（2019～2020）the nitrogen partial factor productivity under plastic mulching did not change significantly at the high soil moisture level,but increased significantly by 20.9%and 25.0%under the medium and low soil moisture levels,respectively.In the wet year（2020～2021）the nitrogen partial factor productivity under film mulching increased significantly by 6.1%under the high soil moisture level,and had no significant changes under both medium and low soil moisture levels.In conclusion,plastic mulching improved wheat grain yield,reduced crop water consumption,and improved water use efficiency.Plastic mulching also promoted the nitrogen uptake of wheat,which significantly improved the nitrogen partial factor productivity and nitrogen uptake efficiency.Pre-sowing soil moisture and film mulching had significant interactive effects on wheat yield and nitrogen fertilizer productivity,in the average year,plastic mulching significantly increased the grain yield and nitrogen fertilizer productivity of winter wheat under medium and low soil moisture levels,while in the wet year,mulching had obvious effect on increasing production and improved the productivity of nitrogen fertilizer under high moisture levels.Thus,plastic mulching could be applied in water conditions.