Simulation Study On Water Amount,Nitrogen Application And Groundwater Depth To Maintain The Steady Growth Of Maize In Hetao Irrigation District

The Hetao Irrigation District is located in Inner Mongolia the arid northwest of China,which is short of water resources and fragile ecology.Unreasonable irrigation and fertilization patterns("the more the better")lead to serious fertilizer loss,reduced water and nitrogen use efficiency,and serious pollution of groundwater,rivers and lakes.In addition,the groundwater depth in this area is shallower all year round,and the shallow groundwater is an important source of soil moisture in arid areas.The contribution of groundwater recharge to crop growth should not be ignored in the process of farmland water conversion and water diversion.Therefore,aiming at the problems of lack of water resources and low efficiency of water and nitrogen utilization in this area,main economic crops of maize in Hetao Irrigation District as the research object.Moreover,two years field experiment in Inner Mongolia Hetao Irrigation District was carried out,which was studied to set out from the different growth period of maize research different water and nitrogen supply on soil moisture and nutrient absorption and utilization of situation,the growth period of maize growth,yield and the effect of water and nitrogen use efficiency.Then,we combined with the AquaCrop model and the DNDC model to simulate the growth period of maize under different situation that are analyzed water use mechanism,soil nitrogen utilization and production change.After that we put forward to maintain the steady growth of maize,the depth of groundwater and the water and nitrogen management mode in Hetao Irrigation District.These results provide the theoretical foundation of the reasonable allocation of water resources,reduce nitrogen non-point source pollution and ensuring the stability of maize growth.The main results are as follows:(1)By analyzing the changes of soil moisture and nutrients under different water and nitrogen treatments at different growth stages of maize,the water consumption modulus of maize at tasseling stage and filling stage can reach more than 65%,indicating that maize at this stage has a greater demand for water.At jointing stage,the soil nitrate nitrogen accumulation decreased significantly,indicating that maize at this stage grew rapidly and needed to absorb a lot of nutrients,and the soil nitrate nitrogen accumulation increased with the increase of nitrogen application rate.In 2019 and 2020,the soil nitrate nitrogen accumulation of CK was 65.7%,30.8%and 23.2%,33.1%,20.0%and 12.5%higher than that of low nitrogen,medium nitrogen and high nitrogen treatments,respectively.Therefore,water and nitrogen resources should be rationally allocated according to the absorption and utilization of water and nutrients in maize to avoid the waste of resources.(2)Irrigation amount and nitrogen application rate had significant or extremely significant effects on plant height,stem diameter,leaf area index,yield and yield components of maize.When water and nitrogen are in short supply,maize plant height,stem diameter,leaf area index,yield and yield components were significantly lower than other treatment,but as the irrigation amount and nitrogen application rate increased to a certain degree,the maize plant height,stem diameter,leaf area index,yield and yield components gradually tends to be stable and even fell,there was no significant difference between the all treatments.(3)AquaCrop model was used to indicate the effects of different groundwater depths on the water consumption and growth of maize at different growth stages.The results showed that comprehensive maize yield,water use efficiency and irrigation water use efficiency of the simulation results,when the local water depth in 1.5～2.5 m,irrigation amount is 279mm,and the priority in the growth period of maize key(jointing stage,tasseling stage and filling stage)for irrigation,the maize yield,water use efficiency and irrigation water use efficiency can maintain at a high level.(4)The DNDC model was used to simulate different nitrogen application rates and topdressing times,and the results showed that,considering maize yield,nitrate nitrogen leaching loss and plant nitrogen uptake,nitrogen application rate ranged from 165.50 kg/hm~2to 200 kg/hm~2 and applied fertilizer at the stage of jointing,tasseling and filling,respectively.This fertilization management could guarantee maize yield and nitrate nitrogen leaching loss in the acceptable range.(5)Based on the above analysis,the suitable irrigation amount and nitrogen application amount to ensure the stable growth of maize in the study area are 279 mm,165.50～200kg/hm~2,and the suitable groundwater depth is 1.5～2.5 m.Moreover,irrigation and nitrogen application should be carried out in the key growth stages of maize(jointing,tasseling and filling stages).