Water Consumption Of Winter Wheat And Its Simulation Under Differentt Lower Limits And Planned Wetting Depths For Irrigation Management

Different lower limits of soil moisture and planned wetting depths have obvious impact on crop growth,development,and absorption and utilization of water and nutrients.By changing the planned wetting depths and the lower limits of soil moisture,the spatial and temporal distribution of root zone soil moisture can be regulated effectively,and water stress in local crop root zone may alsoe be achieved,which thereby may regulate crop yield and quality,and improve water use efficiency.A field experiment was conducted in 2017-2018 and 2018-2019 winter wheat growing seasons to search the optimal lower limit and planned wetting depth for irrigation management in North China Plain.The experiment set 3lower limit of soil moisture levels(40%、 50%、 60% of total available water content,refered respectively as L40、 L50、L60)and 3 planned wet depth levels(60 cm、80 cm、100 cm,respectively refered as D60、D80、 D100).The complete random design is employed and total 9 treatments are combinated.The spatial and temporal distribution of soil moisture under different irrigation lower limits and planned wetting depthes and its effects on growth,development,grain yield and water use efficiency of winter wheat are investigetd and analyszed.Based on the experimental data and the RZWQM2 model,scenario simulations are performed on the lower limit of soil moisture and the planned wetting depth.For exploring the most suitable combination of the irrigation index for local winter wheat production,analyzing the effects of different treatments and optimizing irrigation controlling index also ware carried out furtherly.The research results are helpful to support and guide the scientific irrigation management of winter wheat in the North China Plain.The main findings are as follows:(1)The smaller the depth of the planned wetting depth and the higher the lower limit of soil moisture,the smaller the irrigation quota and the shorter the irrigation interval.Increasing the planned wetting depth will cause more water to accumulate in the deep soil(60-100 cm),while the main root distribution area in the middle and upper layers may be significantly more exposed to water stress.If combined with increasing the lower limit of soil moisture,it can effectively reduce the occurrence of water stress phenomenon.As the planned wetting depth increases,or the the lower limit of soil moisture increases,the total water consumption during the whole growth period of winter wheat will gradually increase.If the planned wetting depth is small,or the lower limit of soil moisture is high,the water consumption of winter wheat will mainly come from the surface and shallow soil(0-40 cm).The greater the planned wetting depth is set,the more water will be stored in the deep soil,and the use of deep soil moisture is not directly proportional to the planned wetting depth,and there is room for water saving.(2)If the planned wetting depth is too high or the lower limit of soil moisture is too low,it will inhibit the growth of winter wheat leaves and the accumulation of dry matter.The treatment with the lower limit of soil moisture of 60% has a relatively large number of grains per panicle.With the decrease of the lower limit of soil moisture,the quality of 1000-grain showed an increasing trend;at the lower planned wetting depth of 60 cm,the quality of 1000-grain was the largest.The higher the lower limit of soil moisture,the higher the grain yield of winter wheat;the grain with the planned wetting depth of 80 cm has the highest yield.The planned wetting depth is reduced,the lower limit of soil moisture is increased,and the water use efficiency of winter wheat is showing a trend of improvement.Under the environmental conditions of this experiment,if the yield is used as the evaluation index,it is recommended to adopt the irrigation control mode of “the planned wetting depth is 80 cm + the lower limit of soil moisture is 60%”(D80L60);if the WUE level is used as the evaluation index,“the planned wetting depth is 60 cm + the lower limit of soil moisture is 50%”(D60L50)or “the planned wetting depth is 60 cm + the lower limit of soil moisture is 60%”(D60L60)is recommended,which can achieve the effect of water saving and stable yield;if IWUE is used as the evaluation index,it is recommended to choose the irrigation control mode of “the planned wetting depth is 80 cm + the lower limit of soil moisture is 40%”(D80L40),which can realize the most efficient use of irrigation water.(3)The RZWQM2 model can be used to more accurately simulate the growth and development and water use of winter wheat under different irrigation control modes in the test site.The simulated water content,LAI and grain yield values of different soil layers are in good agreement with the measured values.The results of the multi-scenario simulation show that the simulated changes in the irrigation conditions of different treatments are completely consistent with the actual irrigation conditions under the corresponding combinations measured in the field experiments.With the increase of the lower limit of soil moisture,the grain yield of winter wheat presents an increasing trend;for the planned wetting depth,the corresponding grain yield will reach the maximum when the value is 55 cm.Considering the simulation results under different combinations of irrigation control indicators,it can be determined that when IWUE maximum is used as the evaluation indicator of the water-saving and stable yield performance of winter wheat production,the optimal combination of irrigation control indicators is “the planned wetting depth is 55 cm + the lower limit of soil moisture is 60%”(D55L60).