Response Mechanism Of Hybrid Maize Seed Production To Water And Nitrogen And Crop Modeling In Arid Northwest China

Aiming at the problem of shortage of water resources and extensive management of agricultural water and nitrogen(N)in the arid northwest China,this thesis takes hybrid maize seed production as the object and adopts the method of field experiment combined with model simulation.The experiment of different irrigation and N treatments and the experiment of deficit irrigation at different growth stages were carried out at the Shiyanghe Experimental Station of China Agricultural University between 2013 and 2015.In addition,Evapotranspiration data measured by eddy covariance(EC)system from 2011 to 2015 and experimental data of deficit irrigation at different growth stages in 2012 were collected.The response mechanism and quantity relationship of hybrid maize seed production to different irrigation and N conditions were studied.The simulation accuracy of the AquaCrop and SIMDualKc model for the evapotranspiration partition was compared.A set of crop parameters of AquaCrop models were obtained for yield forecasting of hybrid maize seed production,and furthermore the AquaCrop model was modified and improved.A total of five aspects of the research results are outlined as follows:(1)The difference in response of water productivity based on biomass(WPB-ET)and yield(WPY-ET)to different water and N conditions were revealed.With the reduction of irrigation amounts WPY-ET significantly decreased but WPB-ET remained stable.Both WPY-ET and WPB-ET tended to decrease under low N supply.Water was the main factor and N the secondary factor in determining yield and final biomass.A higher irrigation level(65-70%field capacity)combined with a lower N rate(100-300 kg N ha-1)was a proper irrigation and N management measure for hybrid maize seed production in the arid northwest China.(2)The effects of different irrigation and N treatments on yield components,biomass partitioning and harvest index of hybrid maize seed production were investigated.Reducing the irrigation amounts significantly decreased the kernel number per plant,while the effect of reducing the N rate was relatively small.100-kernel weight was relatively stable under different irrigation and N treatments.With the reduction of irrigation amount the stem and leaf partitioning index at harvest increased significantly,while the ear partitioning index at harvest decreased significantly.The reduction of N application rate(from 500 to 100 kg N ha-1)did not significantly change the distribution pattern of biomass between organs above the ground.The harvest index was not a constant under different irrigation and N conditions and it was extremely sensitive to irrigation levels.(3)The accuracy of AquaCrop and SIMDualKc models on the ET partitioning of hybrid maize seed production with plastic film mulch in the arid northwest China were compared.Under full irrigation conditions,both AquaCrop and SIMDualKc models showed acceptable accuracy in simulating the daily evapotranspiration(R2 was 0.849 and 0.852,respectively)and crop transpiration(R2 was 0.853 and 0.898,respectively).However,under deficit irrigation conditions,the AquaCrop model had higher accuracy for daily evapotranspiration and crop transpiration simulation(R2 was 0.812 and 0.823,respectively)than the SIMDualKc model(R2 was 0.641 and 0.728,respectively).(4)Parameterization and validation of the AquaCrop model for full and deficit irrigated hybrid maize seed production under plastic film-mulch in arid northwest China were conducted.Parameterized AquaCrop model simulated the changes of canopy cover with acceptable accuracy(R2 and NRMSE were 0.818 and 19.3%,respectively).For biomass accumulation process,the simulated values matched the measured values with R2 and NRMSE of 0.929 and 19.1%,respectively.When the water stress occurs,the model generally overestimated the final biomass,yield and harvest index,and the error of the model increased with the increase of water stress.Parameterized AquaCrop model reflected the trend of soil water content(SWC)well,with R2 and NRMSE were 0.736 and 15.2%,respectively,but slightly overestimated SWC for most treatments.(5)A crop yield simulation model based on the newly established non-linear dynamic normalized water productivity model and the newly established water deficit multiplicative harvest index model was developed.The newly developed water productivity model calculated the biomass with NRMSE decreased by 6.5%and the newly developed harvest index model showed NRMSE reduced by 7.7%.Compared with the original AquaCrop model,the Improved-AquaCrop model showed better performance in simulating yield,with R2 increased from 0.496 to 0.747 and NRMSE decreased from 26.2%to 13.6%.With the increase of water stress,the error of Improved-AquaCrop model was much less than that of the original AquaCrop model.