Response Mechanism And Quantitative Assessment Of Crop To Drought Stress Based On Experiments

Agricultural drought risk management can effectively improve people’s ability to cope with drought and reduce losses of grain yield.Furthermore,the formation mechanism of crop drought loss is the foundation and core of agricultural drought risk management.However,due to so much uncertainty in the crop physiological growth process under drought conditions,the response mechanism of crop to drought stress is extremely complex.Meanwhile,relevant quantitative evaluation methods and realization ways have always been the frontier and difficulty in the field of natural disasters.Huaibei Plain is an important commodity grain base in China,where frequent agricultural droughts severely threaten the regional food security and social stability.Therefore,this study focused on the scientific problems in the response mechanism and quantitative evaluation of crop to drought stress,combining with the crop drought experiments implemented in the Huaibei Plain.Accordingly,the corresponding theoretical methods and empirical applications were conducted.Drought experiment of wheat based on lysimeters and that of soybean planted in pots were implemented in the Huaibei Plain of Anhui Province,a leading grain production region with frequent droughts.The experiments provided observed data for studying the response mechanism and quantitative evaluation of crop to drought stress,combining with the actual crop physiological growth process under drought situations.The quantitative responses of evapotranspiration and accumulated aboveground biomass at each growth stage from drought stress,and also yield components to different drought conditions were analyzed for wheat and soybean.In addition,the linear function between aboveground biomass at harvest time and seed yield,and that between evapotranspiration and accumulated aboveground biomass at each stage from stress were respectively established for soybean.Drought stress at a given stage not only influenced the crop physiological growth during this stage,but also produced a cumulative effect,which transferred the stress effect to the subsequent stages.Moreover,if the stress was not severe,the physiological growth could return to normal by re-watering later.Drought at a given growth stage of soybean directly affected the evapotranspiration,and it further influenced the matter accumulation during this stage by plant physiological growth.There was a certain correlation between the influences of drought stress on soybean evapotranspiration and aboveground growth at each stage from stress.Nevertheless,the farther away from the stage of stress,the weaker the correlation was.The linear function between soybean evapotranspiration and accumulated biomass at a given stage was closely related to the drought situation before.The method for estimating crop evapotranspiration under drought stress during multiple growth stages was built.Meanwhile,the method was combined with the wheat drought experiment.Basal crop coefficients K_{cb ini},K_{cb mid},K_{cb end} and maximum crop coefficient K_{c max} of wheat were optimized by the genetic algorithm,based on the estimation of evapotranspiration under full irrigation,and then the wheat evapotranspiration under drought situations were estimated.The optimized K_{cb ini},K_{cb mid},K_{cb end} and K_{c max} of winter wheat in the Huaibei Plain were 0.32,1.38,0.33 and1.39,respectively.Additionally,the estimated wheat evapotranspiration under full irrigation and five drought stress conditions using the optimized coefficients were all closer to the corresponding measured values,compared with the estimated results based on the coefficients recommended by the FAO-56.The estimation precisions were significantly improved.Furthermore,the estimated wheat evapotranspiration under drought stress based on the optimized coefficients were slightly higher than the observed values,and were not as good as those under full irrigation in general.The soil water stress coefficients calculated by the optimized crop coefficients under various drought situations,were consistent with the corresponding measured wheat evapotranspiration.In a word,the estimation method was reasonable and reliable.The basic connotation and quantitative evaluation method of crop drought sensitivity were proposed.Meanwhile,the method was combined with the soybean drought experiment.Soybean drought sensitivity curves at each growth stage were established from the perspectives of drought influence at a given stage on the plant aboveground growth during this stage and seed yield formation,respectively.Moreover,the soybean drought sensitivity at different stages was compared.The crop drought sensitivity function based on S-shape loss curve could accurately describe the quantitative relationship between the water deficit intensity at a given growth stage and the corresponding crop growth loss,which reflected the formation mechanism of drought loss.From the perspective of drought influence on plant aboveground growth,when the intensity of drought-inducing factor was low,the soybean drought sensitivity at four growth stages ranked from large to small was in the order of flowering-podding stage,seed filling stage,branching stage and seedling stage.However,when the intensity was high,the order changed to seed filling stage,flowering-podding stage,branching stage and seedling stage.In addition,from the perspective of influence on seed formation,soybean seed formation was more sensitive to water deficit during the seedling stage when the deficit was mild,but it became more sensitive to water deficit during the flowering-podding stage when the deficit was relatively serious.Therefore,it is crucial to strictly control the water deficit intensity during the seedling stage and ensure an adequate water supply during the reproductive growth period,especially during the flowering and pod-enlargement stage,so as to guarantee a high soybean yield.An irrigation scheme multi-level optimization system was constructed with the consideration of crop physiological growth process.Moreover,a grey entropy weight method and a grey relation–projection pursuit model were proposed to calculate the weight of evaluation index.Meanwhile,the optimization model was combined with the soybean drought experiment.Then soybean irrigation schemes were evaluated and sorted according to the comprehensive grey relation degree between each alternative scheme and the ideal scheme from different perspectives.When using the entropy weight or projection pursuit method to calculate index weight,it was more effective to calculate the entropy value or projection eigenvalue based on the sequence of the actual study object.According to the order of grey relation degree from large to small in the crop water consumption–crop growth process–crop water use efficiency comprehensive optimization system,the optimal scheme was that with severe-deficit irrigation at the soybean branching stage,and the superiority of this scheme was significant.The worst scheme was that with serious-deficit irrigation at the flowering-podding stage.In addition,the schemes with deficit irrigation during the soybean vegetative growth phase were more effective than those during the reproductive growth phase,and full irrigation during the whole growth period was a moderate scheme.