Study On Water Use Of Winter Wheat And Irrigation Patterns To Cope With Climate Change In Northern China

The shortage of water resources makes deficit irrigation gradually become the main irrigation pattern.It is crucial to explore the effects of different water supply conditions on crop water use processes,especially root water uptake.However,due to difficulties in sampling and other reasons,the law of water uptake by roots after water stress and rewatering is still unclear.With future climate changes,the environmental conditions such as water,heat,and light for crop growth have changed.Quantifying the impacts of these factors on regional agricultural production and reducing the adverse effects of climate change by adjusting cultivation strategies are critical to ensuring food security and efficient use of water resources.In this study,the evapotranspiration?ET?measured by the lysimeter was used as the standard.In different growth stages of winter wheat?Triticum aestivum L.?,the field experiment with three different irrigation levels including no stress?100%ET?,moderate stress?80%ET?and severe stress?60%ET?were set up.On this basis,the agro-hydrological model SWAP?soil-water-atmosphere-plant?was used to simulate the water transport in field.On this basis,this study first analyzed the sensitivity of the parameters in the agro-hydrological model SWAP?soil-water-atmosphere-plant?,and explored the order and direction of model parameter estimation.Then,the calibrated model was used to simulate winter wheat root water uptake and farmland water consumption on a field scale.The process of soil water being uptaken and transformed into evapotranspiration in the SPAC?soil-plant-atmosphere continuum?was studied.Secondly,by coupling the SWAP model with the automatic parameter optimization program PEST?parameter estimation?,the automatic estimation of a large number of parameters was completed,and the application of the model was upgraded to the regional scale from the field scale by combining with Arc GIS software.Finally,the future meteorological data provided by CMIP5?the fifth phase of the climate model intercomparison project?was used to drive the SWAP model.Under two RCP?representative concentration pathway?scenarios,the impact of climate change on wheat growth,water use and yield in winter wheat regions in Northern China was analyzed,and adaptive irrigation patterns were explored.The main results of this study are as follows:?1?The effects of water stress and rewatering on root water uptake of winter wheat were revealed,the main factors affecting root water uptake were obtained,and a root water uptake estimation model was constructed.The cumulative root water uptake in the 0-60 cm soil layer accounts for 89.4%of the total root zone,which is the main source of water uptake by the roots of winter wheat.The cumulative root water uptake in the reproductive growth stage accounts for 56.3%of the total growing season,which is slightly higher than that in the vegetative growth stage.The root water uptake has a certain compensation effect.Water stress and rewatering in the emergence-jointing stage can promote root water uptake,but water stress in other growth stages will inhibit root water uptake.The restoration of root water uptake has the hysteresis effect,and the time is 2-11 d.Winter wheat is more tolerant to water stress in the reproductive growth stage than in the vegetative growth stage,but water stress has a greater impact on the reproductive growth stage,which makes the root water uptake more reduced and the recovery time longer.Therefore,it is necessary to ensure that the soil water content in this growth stage is maintained above 65%of the field capacity.Crop height,net radiation and 0-60 cm soil water content are the key factors affecting the root water uptake of winter wheat.The model established based on them can estimate the root water uptake well?R²=0.836,P<0.01?.?2?The law of water consumption in winter wheat field under different water supply conditions was explored,and the influence of various factors on evapotranspiration was quantified,and an evapotranspiration estimation model was constructed.Under the condition of deficit irrigation,the consumption of soil storage water accounts for 15.99-35.58%of the total water consumption of winter wheat.There is a certain degree of deep leakage in the winter wheat field,and the average water flux at 100 cm soil layer is 14.54mm.The maximum evapotranspiration in winter wheat farmland occurres from the filling stage to the maturity stage,which is 6.21-7.75 mm d^-1.Plant transpiration accounts for 88.40%of the total evapotranspiration,which is the main water consumption method for winter wheat field.Irrigation has a greater impact on plant transpiration,but has a limited impact on soil evaporation.Water stress before jointing has little effect on evapotranspiration of winter wheat,which can often return to normal level after rewatering.However,the evapotranspiration is difficult to recover after water stress during heading-grouting stage.The model constructed with the crop coefficient and water stress coefficient can use a few easily measurable parameters to accurately estimate winter wheat evapotranspiration?R²=0.727,P<0.01?.?3?The sensitivity of SWAP model parameters had been analyzed,and the automatic estimation of SWAP model parameters was completed using the PEST program,which realized the improvement of model application scale.When simulating soil water content and evapotranspiration,the SWAP model is more sensitive to the soil saturated water content?_s and the soil water characteristic curve shape coefficient n in the Van Genuchten model parameters.However,the model is less sensitive to the soil residual water content?_r,the soil water characteristic curve shape factor?and the saturated hydraulic conductivity K_s.After coupling the automatic parameter optimization program PEST with the SWAP model,the automatic estimation of a large number of parameters of the model can be completed.The calibrated model can accurately simulate the soil water content,growth period and yield of winter wheat at each site in the region?MRE is0.99-20.87%,NRMSE is 1.33-25.83%?,which realizes the improvement in the application scale of the model.?4?The impact of future climate on regional winter wheat water use and yield was clarified,and winter wheat variety optimization and irrigation adjustment strategies adapted to climate change were proposed.In the MRI-CGCM3 climate prediction model provided by CMIP5,under RCP4.5 and RCP8.5 scenarios,the net radiation,accumulated precipitation and temperature during the wheat growing season in Northern China increased significantly?P<0.05?.The net radiation and temperature exhibit volatility changes with a period of 10 years.In terms of spatial distribution,there are significant differences in net radiation,accumulated precipitation,and temperature changes at each site?P<0.05?.The temperature rise of 5.39-7.26°C will shorten the growth period of winter wheat,which is mainly reflected in the reduction of the number of days from emergence to heading by 23.9-33.7 d.Under the two RCP scenarios,winter wheat evapotranspiration and yield increase significantly by 41.39%and decrease by 41.71%?P<0.05?,respectively.Path analysis results show that the increase in precipitation and the increase in minimum temperature are the main reasons for the increase in evapotranspiration and the decrease in production,respectively.Based on the simulation results of multiple varieties optimization and irrigation adjustment scenarios,this study suggests that under future climatic conditions,the irrigation quotas for well-irrigation areas and canal-irrigation areas can be 60 mm and 90 mm for winter wheat varieties whose harvest date is delayed by about30 days.In rainy years and normal years,one irrigation?joining stage?and two irrigations?joining stage and heading stage?respectively can increase yield to 38.21%and increase water use efficiency to 44.30%.For drought years,it is necessary to increase irrigation frequency and irrigation quota to avoid production reduction.This study explored the water use patterns of winter wheat in Northern China from the field to the regional scale,and proposed varieties optimization and irrigation adjustment strategies to ensure its yield and water use efficiency under future climate change conditions.However,it is still necessary to continue to compare the differences of various climate prediction models in subsequent studies to further enhance the reliability of the results.