Gaseous Nitrogen Loss And Nitrogen Use Efficiency Of Rainfed Maize As Affected By Nitrogen Application And Its Underline Mechanisms

The application of full film double furrow technology makes corn become one of the main crops in the dry farming area of loess plateau.Application of nitrogen fertilizer is an important means to increase maize yield.Long-term unreasonable nitrogen application has caused low response to fertilization,severe losses of nitrogen in various forms,low nitrogen use efficiency,and the problem of environmental pollution.Therefore,in the pursuit of nitrogen fertilization for increased production,at the same time,it is necessary take into account the nitrogen use efficiency,nitrogen loss and establishing reasonable nitrogen system.Based on the nitrogen fertilizer localization experiment setup in 2012 in the rain-fed farming area of the Loess plateau,the study treatments included four nitrogen levels(no nitrogen,N0,low level is 100 kg·hm^-2,N1,medium level is 200 kg·hm^-2,N2,high level is 300 kg·hm^-2,N3)and fertilizing time and proportion?base fertilizer:jointing fertilizer=1:2 and base fertilizer:jointing Fertilizer:belling fertilizer=1:1:1?.The aim was to study in the corn field gaseous nitrogen losses,nitrogen use efficiency and its underlying mechanism which influence the main research results are as follows:?1?Rational nitrogen application can significantly improve the biological yield and grain yield of maize and increase the nitrogen uptake of maize plants.Biological yield and grain yield of maize with 200 kg·hm^-2 nitrogen application were not significantly different from those applied with 300 kg·hm^-2 nitrogen but increased by 106%and 176%compared with the control group without nitrogen application.The treatment of the fertilizer in proportion did't affect the yield.There was no significant difference in nitrogen accumulation of the whole plant between high and medium nitrogen levels at the mature stage.But the nitrogen accumulation of the whole plant was significantly increased by 306%and 281%compared with the control.?2?With the increase of nitrogen application level,nitrogen surplus,nitrogen apparent loss and soil nitrogen residue all increased,and nitrogen agricultural efficiency?NAE?and nitrogen partial nitrogen productivity?NPFP?of nitrogen fertilizer decreased.The surplus of nitrogen at different nitrogen application levels was significantly increased by 33.5%¹49.4%compared with that without nitrogen application.The apparent loss includes gaseous nitrogen loss and other forms of nitrogen loss,mainly in the form of gaseous nitrogen loss,and the apparent loss rate of high and medium nitrogen level increased by 115%and 49.9%compared with the low nitrogen level.The residual nitrogen in soil after maize harvest also indirectly affects the gaseous nitrogen loss.Compared with 300 kg·hm^-2,the NPFP and NAE of 200kg·hm^-2 increased by 33%and 26%respectively.Fertilization period and proportion had no effect on the above indexes.?3?Ammonia volatilization loss was the main form of gaseous nitrogen loss.Ammonia volatilization and Nitrous oxide emissions at each nitrogen application level accounted for 80%⁹6%and 4%²0%of the total nitrogen gaseous loss,respectively.The higher the nitrogen application level,the higher the gaseous nitrogen loss rate and total amount.With the increase of nitrogen application level,the proportion of Nitrous oxide emission in total gaseous nitrogen loss decreased.The time required for Ammonia volatilization rate to reach its peak at high and medium nitrogen application levels was shorter than that at low nitrogen application levels.The total volatilization of Ammonia at high,medium and low nitrogen application levels increased by 6.5,5.9 and 5.4 times as compared with the control group without nitrogen application.The Ammonia volatilization loss at the jointing stage was significantly reduced by 37%at the first application.The Nitrous oxide emission fluxes at high and medium nitrogen levels were significantly increased compared with the control group.The Nitrous oxide emission flux could be significantly reduced by 18.2%⁵9.2%after partial fertilizer application.Nitrous oxide emission and Ammonia volatilization were mainly affected by the amount of nitrogen fertilizer applied in the season.In addition,Nitrous oxide emission was also significantly related to the residual mineral nitrogen in the before sowing 0¹40cmsoil.To sum up,in the dry farming area of loess plateau,the yield of maize increased with the increase of nitrogen application,but the yield no longer increased significantly when the nitrogen application exceeded 200 kg·hm^-2.Gaseous nitrogen loss dominated the apparent nitrogen loss of corn farmland,while gaseous nitrogen loss was dominated by ammonia volatilization.As higher nitrogen application level leads to more nitrogen surplus,more ammonia volatilization loss and more soil nitrogen residue,leading to lower nitrogen utilization efficiency,and the one-time dressing at jointing stage can reduce the loss of nitrogen in the form of ammonia volatilization.Therefore,in order to give consideration to high yield,low nitrogen loss and high nitrogen utilization efficiency in maize production in the dry farming area of the loess plateau,it is suggested to apply about 200 kg·hm^-2 of pure nitrogen and reduce the number of fertilizer application.