Mechanism Of Maize Staged Water Deficit And Its Simulation Under Drip Irrigation In Shallow Buried Soil

In recent years,with the increasing of agricultural water’s consumption,the overdraft problem of groundwater has increasingly became serious in the Xi Liao River Basin.It is necessary to restrict the use of agricultural water resources.Instead,the concept of water saving priority should be implemented,so only with appropriate irrigation technology and scientific and reasonable water control measures can we stabilize production and save agricultural water resources.Based on local background and needs,around the optimization of maize irrigation technology in Xi Liao River Basin,and the regulation mechanism of water deficit by stages on crop growth and water utilization,the comparative selection of agricultural water model and the parameter sensitivity and simulation accuracy in the process of use.The studies of field experiments and model simulation were carried out,the main conclusions were obtained as follows:1.Film drip irrigation increased the leaf area index and shortened the time of population canopy development in the early and rapid growth periods of maize compared with film-free drip irrigation.Within 75 days after sowing,filming increased the soil water storage at the 1 m soil layer by 3.9%-15.7%.After the canopy was fully developed,soil water storage was close to or less than that of bare land.The soil temperature decreased sharply after irrigation and effective rainfall,and recovered subsequently.The soil heat showed alternating cycle fluctuation with water supply and consumption changes.Filming significantly increased the soil temperature in the early and rapid growth periods.Because of film mulching,the 5 cm soil layer obtained more than 44.92℃ daily average soil accumulated temperature within 75 days after sowing,which was significantly reflected in water accumulation and heat loss(after well irrigation and rainfall)of the soil to the soil temperature recovery period.Filming could stabilize the soil temperature amplitude and obtain more soil accumulated temperature when the soil was cold.According to comprehensive benefit analysis,drip irrigation under mulch only scored first in terms of technical effects,while drip irrigation in shallow buried soil received the highest score for economic benefits(0.369)and the highest score for environmental benefits(0.577)to make its total score(1.012)ranked first.2.When the values of Dual Crop Coefficient model parameters were fluctuated within±10%,the maximum soil evaporation was 18.72%higher than the minimum value,the maximum crop transpiration was 25.37%higher than the minimum value,and the maximum evapotranspiration was 19.9%higher than the minimum value during the whole growing season of maize.When the total soil evaporation in the whole growing season of maize was simulated,the sensitive parameters were evaporable water on soil surface and basic crop coefficient of middle growth period,and their corresponding global sensitivity indexes were 0.662 and 0.321,respectively.Their global sensitivity indexes were 33.6-69.4 times higher than the mean of insensitive parameters.When the total crop transpiration during the whole growing season was simulated,the sensitive parameters were the threshold of soil water storage of roots free from water stress,basic crop coefficient of middle growth period and field water capacity,and their corresponding global sensitivity indexes were 0.569,0.485 and 0.455,respectively.Their global sensitivity indexes were 34.5-43 times higher than the mean of insensitive parameters.3.The model of AquaCrop and Dual Crop Coefficient were more similarly express The process of maize consumption of soil water during the period of maximum canopy development without beginning to decay.However,the simulation of SWS with water storage in 1m soil layer during the rapid growth period and the later period was greatly different.Dual Crop Coefficient model underestimates SWS in more cases,and the AquaCrop model simulates an even distribution of positive and negative bias but overestimates it when the SWS is too low.The capacity of AquaCrop model to describe the variation of evapotranspiration ETstage at each growth stage due to water deficit was slightly better than that of Dual Crop Coefficient model and the RMS errors NRMSE of the two models were 8.158%～9.510%and 5.980%～15.022%.The simulation accuracy of AquaCrop is slightly better in general,and it is recommended to be a maize water management model which suitable for drip irrigation in shallow buried soil.4.The minimum effect of water deficit(0.6ETc)in different stage on maize canopy coverage CC was DI-α,which did not affect the canopy level at reproductive stage.Water deficit DI-β decreased the rapid growth period of CC and continued to affect to the reproductive stage.The middle period of water deficit DI-γ would reduce the duration of canopy maintenance at the maximum level and cause the canopy premature senility.At the rapid growth and the middle stage of DI-αβ significantly decreased CC which was in reproductive stage.At the rapid growth and the middle stage of DI-βγ weakened the canopy deepest.Compared with full irrigation of FI in the whole growth period,single stage water deficit decreased 3.27%～10.91%of the final biomass B,and the continuous water deficit in 2 stages reduced B by 16.84%～25.86%.The grain yield of maize Y which in different stages of water deficit and different situations from high to low was DI-α,DI-(β,DI-γ,DI-αγ,DI-αβ,DI-β,DI-βγ,the initial water deficit had no significant effect on grain yield.Water deficit in early stage or rapid growth stage can promote more nutrients to be transformed into grains,while water deficit in reproductive stage will reduce harvest index HI,and water deficit in 2 stages would reduce HI in different situations,and under different conditions,water deficit in 2 stages reduced HI.During the rapid growth of canopy,water loss would affect the middle evapotranspiration of ETmid and weaken the transpiration capacity in reproductive stage,while the initial loss of water did not decrease ETmid.The effect of early water deficit on ET was the least,and water deficit during the rapid growth of canopy or single growth stage of reproductive process significantly reduced ET.Compared with the full irrigation FI,the ET of DI-αβ and DI-βγ decreased by 10.40%～12.32%and 12.01%～13.14%respectively in the 2 successive stages.Initial water deficit can improve WUE,and it was significantly higher than that of single stage water deficit in reproductive stage,and the 2 stages continuous water deficit had a significant negative effect on Y and WUE,and WUE of rapid growth stage and middle stage continuous water deficit was the lowest.Water deficit(0.6ETc)in the early growth stage can save water,increase efficiency and stabilize production,which is the best way to control water deficit.5.The original parameters of AquaCrop model can not effectively describe the changes of crop system caused by different stages of water deficit.A set of modified model parameters obtained in this study can obtain better simulation accuracy.The average absolute error MAE of each simulated indicators are 25.39%～67.08％lower than the original parameters,respectively.The model has high simulation accuracy when the measured values of CC and Bi(time-varying biomass)are low and high,while The simulation error of CC rapid change stage is large,and the biomass was significantly overestimated in the first half of rapid growth of stems and leaves.The NRMSE of simulated full irrigation CC was 7.523%～9.865%,and the NRMSE of the simulated single-stage and adjacent the 2 stages continuous water deficit CC were 6.395%-18.714%,11.935%-19.537%.In the Bi simulation,the NRMSE of full irrigation,single stage deficit,and successive 2 stages deficit were 10.718%～11.810%,12.852%～20.372%,and 17.588%～26.033%.The AquaCrop model was more effective to simulate full irrigation during the whole growth period,and the error increases when there was water deficit.The simulation accuracy of corn growth,yield and water use was significantly reduced under the 2 stages continuous water deficit.It is necessary to pay attention to this disadvantage when using the model to avoid decision-making errors,and this model still needs to be improved in terms of mechanism to describe the response degree of water deficit.