Effects Of Nitrogen Reduction And Water Saving On Winter Wheat Yield,Water And Nitrogen Use Efficiency In Guanzhong Plain

The Guanzhong Plain is an important grain production region in China.Excessive nitrogen application,insufficient water resources and uneven spatial-temporal distribution of precipitation are important obstacles to the local agriculture's realization of green and sustainable development,which seriously affects the normal growth and development of domestic winter wheat and its yield.Study the growth and development of wheat,grain yield,water and nitrogen utilization in the Guanzhong Plain under nitrogen reduction and water saving·conditions.On the basis of ensuring yield,improve water and nitrogen use efficiency,reduce nitrogen and water loss,which is of great significance to maintain soil fertility,and nitrogen leaching loss,achieve agricultural cost-savings and efficiency-increasing,and promote agricultural green development.The three-factor split-plot field experiment?2017-2019?was conducted in Cao Xinzhuang Experimental Farming of Northwest Agriculture and Forestry University of Science and Technology,Yangling District,Xianyang·city,Shaanxi Province,where the nitrogen application rates are N300(300 kg·ha^-1),N225(225 kg·ha^-1),N150(150 kg·ha^-1),N75(75 kg·ha^-1),N0(0 kg·ha^-1),the irrigation treatments are W2(1200 m³·ha^-1),W1(600 m³·ha^-1),W0(0 m³·ha^-1),the tested varieties are Xi Nong 979 and Pu Bing 151.Under different water and nitrogen treatments,to study the winter wheat growth,yield and yield components,the dynamics of soil water content,water and nitrogen use efficiency,the distribution characteristics and the leaching situation of soil nutrients and nitrate nitrogen were studied.The main results of the study were as follows:1. Adding nitrogen fertilizer can effectively increase the aboveground biomass,LAI,and plant nitrogen content of winter wheat,which were maintained at a high level under N150,N225,and N300 treatment;increasing irrigation can increase aboveground biomass,LAI and plant nitrogen content,and each indicator of irrigation treatment is significantly greater than W0 treatment,between W1 and W2 treatment,each indicator under W2treatment was sometimes slightly lower than W1 treatment,sometimes the increment was not significant.From the perspective of water use efficiency,W1 treatment is appropriate.In terms of varieties alone,Pu Bing 151 was more dominant in accumulating biomass.2. The yield was higher under N150 and N225,but there was no significant difference.In the two-year experiment,irrigation treatment increased yield by 9.4%to 11.9%and 2.64to 2.69 times compared to no-irrigation treatment,the yield difference between the W1 and W2 treatments was not significant,but the wheat lodging phenomenon existed in the W2treatment.From the perspective of water use and economic benefits,combined with the actual situation in the field,it was appropriate to irrigate 600 m³·ha^-1 during the over-wintering period.Under the irrigation of 600 m³·ha^-1,the maximum yield and net income can be obtained by applying nitrogen 150 kg·ha^-1 in 2017-2018;although the yield and net income were the highest under the nitrogen application of 225 kg·ha^-1 treatment in2018-2019,the yield of the two varieties treated with the nitrogen application amount of 150kg·ha^-1was only reduced by 7.4%and 6.7%compared to the nitrogen application of 225kg·ha^-1;the net income only decreased by 8.4%and 7.4%.Among the two varieties,the yield and economic benefits of Pu Bing 151 were slightly higher than Xi Nong 979 under the same treatment.3. With the increase of nitrogen application,nitrogen agronomic efficiency?NAE?,nitrogen recovery efficiency?NRE?,and nitrogen use efficiency?NUE?all decreased,whereas,WUE showed a trend of increasing first and then decreasing.Can make the water and nitrogen use efficiency can keep at a high level?N150?.With the increase of irrigation volume,the dynamics of soil water content in 0?60 cm were most actively,followed by the water content of the 80?140 cm depth,but below 140 cm is relatively stable,the change of soil water content under different irrigation treatments is W2>W1>W0;between W1 and W2,the water use efficiency is expressed as W1>W2.Therefore,nitrogen application of 150kg·ha^-1 and irrigation of 600 m³·ha^-1 during the over wintering period can achieve higher yield and economic benefits on the basis of higher NUE and WUE.The NUE showed no difference between the two varieties,but WUE of Pu Bing 151 was better than Xi Nong 979.4. With the amount of nitrogen applied increases,the accumulation of nitrate nitrogen and the amount of leaching also increased.Nitrate nitrogen driven by irrigation to the deeper soil.Nitrate nitrogen was integrated in the 0?60 cm under the W0,and mainly distributed in the 80?200 cm under W1 treatment,the accumulation peak of nitrate nitrogen fluctuated at160 cm also;the nitrate nitrogen accumulation peak moved down below 200 cm of W2treatment.It demonstrated that the greater irrigation volume,the deeper of leaching peak,and the greater of the soil nitrate nitrogen leaching.5. Over-wintering stage of the irrigation 600 m³·hm^-2,N150 both and fitting under the condition of the optimum N application or N225 comparison in the process of production,NUE is promoted,nitrate leaching amount also declined significantly.In summary,in the Guanzhong Plain area,the 600 m³·ha^-1 irrigation during the over-wintering period,and reduce the nitrogen application by 50%to 150 kg·ha^-1nitrogen,it not only supply water and nutrients required for wheat growth,also improve water and nitrogen use efficiency,which can obtain higher yield and economic profits,as well can maintain a relatively stable soil fertility and reduce nitrate nitrogen leaching losses.Therefore,it can be used as a recommend method for nitrogen application and irrigation amount in wheat production in the Guanzhong Plain.