Effects Of Water Saving And Nitrogen Reduction On Summer Maize Yield And Water And Nitrogen Use Efficiency In Guanzhong Plain

In the current summer maize production,insufficient irrigation water resources and excessive nitrogen application not only seriously waste water and fertilizer resources,but also adversely affect the ecological environment of farmland.This study intends to analyze the influences of nitrogen reduction and water saving modes on summer maize growth,yield,water and nitrogen utilization,soil nitrate nitrogen distribution and residual status.Meanwhile,we construct and verify the critical nitrogen concentration dilution curve of summer maize under different irrigation conditions.It aims to provide a basis for the production model of summer maize in the Guanzhong Plain to decrease irrigation and nitrogen amount,and increase the efficiency,and accelerate the sustainable and green agricultural development.A field trial on water and nitrogen reduction in summer maize was carried out in Yangling,Shaanxi at 2018 and 2019.Three irrigation treatments were conventional irrigation(800 m³ hm^-2),reduced irrigation(400 m³ hm^-2)and no irrigation(0m³ hm^-2);and five nitrogen treatments were as follows:conventional N application(300kg N hm^-2),reduced 25%(225 kg N hm^-2),reduced 50%(150 kg N hm^-2),reduced 75%(75kg N hm^-2)and no N fertilizer(0 kg N hm^-2),respectively.The tested varieties are Zhengdan958 and Xundan 20.The aboveground growth,yield and its components of summer maize,soil water dynamics,water and nitrogen use efficiency,the residual characteristics of nitrate nitrogen distribution during maturity were analyzed under different water and nitrogen treatments.At the same time,a critical nitrogen concentration dilution curve model was constructed.The main research results of study are as follows:（1）Appropriately reducing the amount of nitrogen and irrigation will not have a significant impact on the growth of summer maize.Compared with the conventional water and nitrogen model,under reduced irrigation and 25%nitrogen reduction,the dry matter accumulation process of summer maize is reasonable,and the dry matter accumulation during maturity is not reduced;it has no significant effect on the leaf area index（LAI）of maize,meanwhile increased obviously before anthesis and slow down the rate of decline of LAI after anthesis;and kept a higher net photosynthetic rate from the tasseling stage to the maturity stage;it has no significant effect on the SPAD value;the aboveground plant nitrogen content change process is reasonable in following stage.（2）Appropriately reducing the amount of nitrogen and irrigation did not obviously reduce the yield,and improved the quality and profitability.Compared with conventional irrigation（W2）,non-irrigation decreased the yield of Zhengdan 958 about 17.3%,and the yield of Xundan 20 was significantly reduced by 14.3%,there is a risk of production reduction.However,the reduced irrigation did not obviously influce the grains per ear,number of ears,and 100-kernel weight,and did not reduce the yield;there was no significant difference between the 25%nitrogen reduction and the conventional nitrogen application in summer maize yield and yield components.A 25%reduction in nitrogen under reduced irrigation has a certain effect on the quality of grains.The two-year average income of Zhengdan 958increased by 1,048 yuan hm^-2 compared with conventional water and nitrogen treatment,and Xundan 20 increased by 2,151 yuan hm^-2.（3）Reducing the amount of irrigation and nitrogen application obviously improved the water and nitrogen use efficiency of summer maize.The soil moisture content of conventional irrigation has always remained high from maize jointing stage.The soil moisture below 80 cm has a tendency decrease.The moisture content of each soil layer gradually increases in the mature period and basically maintained above 18%,which has a significant effect on soil water replenishment;The soil moisture content of conventional irrigated maize is always high from the jointing stage,its tends to decrease below 80 cm in some stage and gradually increases at the maturity stage of each soil layer,basically maintaining above 18%,which has a supplementary effect on the soil moisture,Significantly.Reduced irrigation treatment of summer maize in all stages of soil moisture content was lower than conventional irrigation,but the shallow soil moisture content in the mature stage was significantly higher than that before planting,which also played a role in supplementing water.WUE increased first and then decreased with the increase of nitrogen and irrigation application rates.NAE,NRE and NUE decreased with the increase of nitrogen application rates.Compared with conventional water and nitrogen combination（W2N300）,The two-year average WUE of ZD958 and XD20 was significantly increased by 20.9%and 31.6%,respectively,under reduced irrigation and 25%nitrogen reduction.NAE was significantly increased by 51.1%and 25.7%,repectively;NRE was significantly increased by 8.4%and 5.9%,and NUE was significantly increased by 21.2%and 13.7%,repectively.（4）The nitrate-nitrogen content in the 0～200 cm soil profile after summer maize harvest increases with the increase of nitrogen application rate.The average annual nitrate nitrogen residue amount of ZD958 and XD20 decreased by 25.2%～86.8%and 30.2%～87.6%;the accumulation peak of nitrate nitrogen gradually moved to the lower soil with the increase of irrigation,and the leaching phenomenon of conventional irrigation and nitrogen treatment was most obvious.Combined with the analysis of the relationship between yield,nitrogen use efficiency and residual nitrate nitrogen,the comprehensive performance of207～210 kg hm^-2nitrogen application is better under reduced irrigation.（5）There was a exponential relations between nitrogen concentrations（Nc）and aboveground biomass under different irrigation conditions(W0:Nc=35.04DM^-0.27;W1:Nc=37.15DM^-0.31;W2:Nc=33.36DM^-0.37),W1 had high nitrogen uptake and appropriate nitrogen concentration dilution rate.The relatively stable model had a linear correlation between the fitted and actual plant N concentrations,the evaluation index root mean square error and normalized root mean square error of the fitted model were 2.14,1.45,1.30 and9.90%,7.48%,8.24%,respectively,with fine stability among years.NNI was W1>W2>W0under different irrigation.NNI increased with the increase of nitrogen application at different growth stages.When the NNI was close to“1”under W0,W1 and W2 treatment,the nitrogen application rates were 225,150～225 and 225～300 kg hm^-2,respectively.NNI was significantly positively correlated with yield,negatively correlated with the agricultural utilization efficiency of nitrogen fertilizer,and was significantly correlated with relative yield.Therefore,NNI could further explain the yield changes under different water and nitrogen conditions.In this study,the critical N dilution curve and N nutrition index,which is of great significance for N diagnosis and water and fertilizer management of summer maize.Therefore,considering the yield level,water and fertilizer use efficiency,plant nitrogen nutrition status,and nitrate nitrogen residues,it is recommended to reduce nitrogen application by25～30%in summer maize production in Guanzhong Plain,that is,nitrogen application is 200～225 kg hm^-2,irrigate with 400 m³ hm^-2 during the jointing stage.It can achieve the goal of water saving and nitrogen reduction that takes into account crop yield and ecological benefits.