Quantitative Analysis Of Reactive Nitrogen Losses And Nitrogen Use Efficiency Of Three Major Grain Crops In China

Developing ecologically optimal nitrogen management integrating agronomic, economic, and environmental aspects is urgent to ensure national food security and protect resources and environment. However, there is shortage of quantitative analysis of reactive nitrogen losses and nitrogen use efficiency of major crops in China at regional scale.In this study, based on collecting literature data and field experiments fro several years, we focus on reactive nitrogen losses (Nr) of major cereal crops in different regions and their influence factors, the development and application of empirical model for estimating reactive nitrogen losses. Finally, we comprehensive understand nitrogen recovery efficiency of major crops in China at regional scale and the influence factors. The main results were concluded as follows:1. N leaching was the highest and N2O emission was the lowest for major cereal crops. Cross major cereal crops, N leaching loss and rate were average27.2kg N ha-1and12.6%, NH3volatilization loss and rate were average20.7kg N ha-1and11.2%, N2O emission loss and rate were average1.86kg N ha-1and1.0%. N2O emission losses and rate were the highest as2.68kg N ha-1and1.49%for wheat, N leaching losses and rate were the highest as47.6kg N ha-1and20.8%for maize, NH3volatilization losses and rate were the highest as35.2kg N ha-1and17.2%for maize,2. There was great variation of Nr losses in different regions. For N2O emission, single rice in Yangtze river basin and winter wheat in south of China were the highest, N2O emission were1.89and3.46kg N ha-1, N2O emission loss rate were0.84%and1.92%. There was no significant difference of N2O emission among different regions for maize. For N leaching, single rice in Yangtze river basin and winter wheat, summer maize in North China Plain were the highest, N leaching were16.8,34.1and58.3kg N ha-1, N leaching loss rate were4.5%,15.6%and24.9%. For NH3volatilization, late rice in southern China, winter wheat in south of China and summer maize in North China Plain were the highest, NH3volatilization were54.9,13.1and15.0kg N ha-1, NH3volatilization loss rate were35.2%,9.2%and8.5%.3. Both N2O emissions and N leaching increased exponentially with the N application rate or N surplus, while NH3volatilization increased linearly with the N application rate. Estimated Nr losses were higher by N-R than those estimated by the N-S, especially for high-yield, high-REN systems. Across on-farm experimental of wheat and maize in North China Plain, an in-season root-zone N management strategy with a60%and39%lower N application rate and5%and6%higher grain yield increased the REN by146%and98%and reduced Nr loss intensity (based on the N-S) by80%and45%compared to farmers’ typical N practices for wheat and maize, respectively.4. For winter wheat in Henan province, compared with economically optimal N rate as225kg N ha-1, ecologically optimal N rate was201kg N ha-1, Nr losses intensity decreased15%without yield losses. For summer maize, compared with economically optimal N rate as237kg N ha-1, ecologically optimal N rate was185kg N ha-1, without yield losses. Ecologically optimal N rate significantly increased with the increase in N-increased yield.5. The nitrogen recovery efficiency (REN) of major cereal crops decreased from1990-1999as35%to2000-2005as27%and then increased to34%in2006-2010. For rice, REN were37%,28%and37%in the three years. For wheat, REN were34%,28%and35%in the three years. For maize, REN were35%,26%and30%in the three years. There was great variation of REN in different regions. For rice, REN of single rice in north China was the highest as40%. Winter wheat was the highest as38%. The order of REN for maize in size was Northeast China (32%)> summer maize in North China Plain (29%)> maize in Southwest China (25%).