Simulation Variation Characteristics Of Wheat Yield And Soil Water,carbon And Nitrogen Evolution Under Drought Stress

With the frequent occurrence of global extreme climate events,the agricultural production is facing an increasing threat in the Loess Plateau Gully Region of central Gansu.The reduction and harvest failure of agricultural production induced by the frequent droughts,it was urgent to take appropriate farmland management measures to promote the efficient utilization of the regional agricultural water and soil resources.Taking the typical Semi-arid Loess Plateau Gully Region of central Gansu as the study area and the dry land spring wheat as the study object,we carried out the research by the field experiments about different growth periods,degrees,and duration of drought stress and combined with crop model simulation.The suitable management measures of the Loess Plateau Gully Region of central Gansu under different drought stress were discussed.The response laws of spring wheat yield,water and nitrogen use efficiency under different drought stress were studied.The dynamic characteristics of soil moisture,carbon and nitrogen transport under different drought stress were defined.These studies will provide the basis for the efficient use of water resources in the region.The following main results have been concluded:1.The APSIM model could better simulate yield formation process of spring wheat under different drought stress in the semi-arid region of central Gansu,the simulation of soil water content,nitrate nitrogen content in 0～110cm soil layer and soil organic carbon content in0～50cm soil layer had high simulation accuracy.The values of the average root mean square error（RMSE）,normalized root mean square error（NRMSE）and model effectiveness index（M_E）of the grain number of the simulation model were 167.05 number·m^-2,3.27%,and 0.76,respectively;the values of the average RMSE,NRMSE and M_E of thousand-grain weight of the simulation model were 1.29g,3.87%,and 0.59,respectively;the values of the average RMSE,NRMSE and M_E of the yield of the simulation model were 107.34kg·hm^-2,4.52%,and 0.69,respectively.In the 0-110cm soil layer,the values of the average RMSE,NRMSE and M_E of the soil water content of the simulation model were 1.57%,9.55%and 0.62,respectively;In the 0-50cm soil layer,the values of RMSE,NRMSE and M_E of the soil organic carbon content of the simulation model were 1.34g·kg^-1,15.85%and 0.79,respectively.In the 0-110cm soil layer,the values of RMSE,NRMSE and M_E of the soil nitrate nitrogen of the simulation model were 0.93g·kg^-1,12.31%and 0.64,respectively.2.The spring wheat had the worst tolerance to drought stress at jointing stage.With the increase of times of drought stress,the tolerance of spring wheat to drought stress decreased.When drought stress occurred at jointing stage,heading stage and grain filling stage,the yield of spring wheat decreased.When continuous drought stress occurred from emergence to tillering stage,and the amount of supplementary irrigation was less than 100mm in the later stage,the yield of wheat significantly decreased.However,the moderate drought stress was beneficial to improve the yield of spring wheat at tillering stage.When the irrigation amount reached 400mm,the maximum yield reached 4631.00kg·hm^-2.3.When the drought stress occurred at reproductive growth stage,the evapotranspiration of farmland system would increase,this would lead to decrease of soil water content.The drought stress had significant influence on the change of soil water content at grain filling stage during wheat growth period,the moderate drought stress was beneficial to improve the soil water content at emergence and tillering stage.When the amount of irrigation was less than 200mm,the variability of soil water content in 0-30cm soil layer was greater than other soil layers,and it was apt to form the highest peak of soil water content.The soil water content was related to the occurrence period of drought stress in 30-110cm soil layer.When drought stress occurred at the vegetative growth stage,the soil water content gradually increased with the soil layer depth.However,when drought stress occurred at the reproductive growth stage,the soil water content gradually decreased with the soil layer depth.When the amount of irrigation was 300-500 mm,the soil water content increased slowly with the depth of soil layer,and the difference was not significant between 400mm and 500mm.4.The soil organic carbon content decreased with the growth and development of spring wheat.The soil organic carbon content would be improved under the drought stress at heading stage,flowering stage,and grain filling stage.The soil organic carbon content reached the maximum values of 8.03g·kg^-1 under the drought stress at flowering stage.The soil organic carbon content showed a trend of firstly increased and then decreased,when the irrigation amount reached 200mm,it reached the maximum value of 8.00g·kg^-1.5.The nitrate-nitrogen uptake would be improved under the drought stress at heading,it could reduce the nitrate-nitrogen content in the surface soil,and also reduce the risk of nitrate nitrogen leaching into the deep soil.When the amount of irrigation reached 200mm,the nitrate-nitrogen uptake reached the maximum value of 163.98kg·hm^-2.Different irrigation changed the distribution of nitrate-nitrogen in soil profile,it showed under the amount of irrigation less than 200mm,the soil nitrate-nitrogen was mainly concentrated in the surface of soil.When the amount of irrigation was 300-500 mm,nitrate-nitrogen content decreased significantly in soil surface,and it had obvious transport in 0-110cm soil layer.6.The water use efficiency and nitrogen use efficiency of spring wheat would be improved under drought stress at emergence stage and tillering stage,but the drought stress after tillering stage had adverse effects on the water use efficiency and nitrogen use efficiency of spring wheat.The water use efficiency and nitrogen use efficiency showed a trend of firstly increased and then decreased,when the amount of irrigation reached 300 mm in the growth period,the water use efficiency and nitrogen use efficiency reached the maximum values of12.94kg·mm^-1 and 32.04kg·kg^-1,respectively.The study confirmed the model’s description ability on the growth and development process of wheat,soil moisture,carbon,nitrogen transport in the Loess Plateau Gully Region of central Gansu.It also expounded the response laws of wheat production,soil moisture,carbon,and nitrogen to water limits factors in semi-arid regions with.This study held significance and application value for improving the water use efficiency of Dryland Spring Wheat in the study area.