The Study On The Emission Characteristic Of Farmland Nitrogen In Typical Cropping Patterns

The North China Plain is one of the most important food crop production bases in China,with winter wheat,summer maize and soybean being the main crops in agricultural production.It is also one of the areas with the highest fertilizer application rate.Fertilization can increase crop yields,at the same time,it results in serious environmental costs.Therefore,it is urgently needed to be solved to balance the reducing of environmental cost while achieving high crop yield in North China area.In this study,based on results from different nitrogen（N）fertilization rates experiment in winter wheat and summer maize and track the farmers,using the nutrient flow model and geographic information system tools,systematically investigated the yield-improving effects,N emission characteristics and the main influencing factors of winter wheat-summer maize and winter wheat-soybean rotation system,to explore the mitigation strategies and potential of crops N emission,in order to provide evidences for increasing crop yield and nutrient use efficiency,controlling environmental pollution risk and keeping sustainable agricultural development.The main results are summaried as follows:（1）Compared with N₀ treatment,grain yield was increased by 6.1%,7.3%,7.3%and7.0%in N₁₅₈,N₂₂₅,N₂₇₀ and N₂₉₃ treatments in wheat wheat,respectively,while was increased by 23.5%,30.9%,32.1%and 25.5%in N₁₅₈,N₂₅₅,N₂₇₀ and N₂₉₃ treatments in summer maize,respectively.Winter wheat and summer maize got the highest yield at N225and N₂₇₀ level,respectively.Nitrogen fertilization with reasonable rate could significantly increase crop yield,but excessive N application is not conducive to the improvement of crop yield.From the apparent surplus and deficit of soil N,the apparent surplus and deficit increases with the increase of N application.In winter wheat season,the N₀ treatment was deficit,the other treatments were surplus.In summer maize season,N0 and N158 treatments were deficit,but N₂₂₅,N₂₇₀ and N₂₉₃ treatments were surplus.（2）The soil nitrate-N content in 0-200 cm depth in different treatment showed the characteristics of the increase in winter wheat season and the decrease in summer maize season,and the nitrate-N content in different depths increase with the increasing of N fertilizer.After basal fertilizer application for winter wheat,the cumulative ammonia volatilization of N₀ and N₂₂₅ treatment was 0 and 3.2 kgN/hm²,respectively,and the N loss rate of N₂₂₅ was 2.9%.After the second fertilizer application of winter wheat,the cumulative ammonia volatilization of N₀ treatment was zero,the accumulations of other N treatments showed that:N₂₇₀>N₂₂₅>N_{270 no irrigation},the values were 31.7,27.8 and 26.5 kg N/hm²,and N loss ratio of them were 56.4%,49.5%and 47.1%,respectively.After basal fertilizer application for summer maize,the accumulated ammonia volatiles of each treatment were basically:N₂₇₀>N₂₂₅>N₀,its value was 31.6,24.5,11.0 kg N/hm²,and the N loss rate of N₂₇₀ and N₂₂₅ was 7.61%and 5.99%respectively.（3）The N emission in winter wheat season was mainly ammonia volatilization,followed by nitrate N leaching,and the emission of nitrous oxide was relatively small.The environmental loss of N fertilizer in summer maize season was mainly nitrate-N leaching,followed by ammonia volatilization,and the emission of nitrous oxide was relatively small.The amount of ammonia volatilization and nitrous oxide emission of soybean land was lower than 5 kg N/hm².（4）In winter wheat season,the ammonia volatilization,nitrous oxide emission,and nitrate leaching would increase by 9.6,0.3 and 2.0 kg N/hm² with N fertilization rate increment by 100 kg/hm²,respectively.When the irrigation increases one time,the intensity of nitrous oxide emission and nitrate leaching intensity will increase by 0.1 and1.7 kg N/hm²,respectively.In the summer maize season,if the amount of N fertilizer increase 100 kg/hm²,ammonia volatilization,nitrous oxide emission and nitrate N leaching will increase by 12.6,0.9 and 30.5 kg N/hm²,respectively.For each increment of irrigation,the intensity of nitrate leaching will increase by 18.6 kg N/hm².In the soybean season,the amount of N fertilizer will increase by 100 kg/hm²,and ammonia volatilization and nitrous oxide emission will increase by 3.1 and 0.9 kg N/hm²,respectively.The intensity of ammonia volatilization and nitric oxide emission will increase by 0.6 and 1.2 kg N/hm²,respectively.（5）The N emission intensity from winter wheat,summer maize and soybean fields was 99 kg N/hm² in XinAn village during 2016-2017 crop season,and the N emission intensity in winter wheat season was the highest,and it was 53.2 kg N/hm².The N emission intensity in summer maize season was 43.9 kg N/hm².The N emission intensity in soybean season was the least,it was only 1.9 kg N/hm².Optimizing the N application,planting,irrigation times and spray insecticide times can improve crop yield and reduce the N emissions.The emissions reduction potential of winter wheat was 1.9 kg N/hm².The emissions reduction potential of summer maize was 2.4 kg N/hm².The emissions reduction potential of soybean was 0.5 kg N/hm².By turning the winter wheat-summer maize rotation into winter wheat-soybean rotation,the N potential could be reduced by 40 kg N/hm²,while the profit of crop planting decreased by 43 yuan/hm².（6）Under the management measures of high yield,the emission of farmland nitrogen can be reduced by reducing the N fertilization rate and irrigation times of winter wheat and summer maize.In the winter wheat season,when N inputs were between 184 and 234kg/hm²,the yield will decrease by 15,44,72,101 and 130 kg/hm²,respectively,with the decrease of N input by an increment of 10 kg/hm².The N emission intensity will decrease by 0.7,0.6,0.5,0.4 and 0.3 kg N/hm²,respectively.When the irrigation was conducted 2-7times,the yield will decrease by 50,246,443,639,835 kg/hm²,respectively,and the N emission intensity will reduce by 3.8,3.8,1.8,1.8 and 1.5 kg N/hm²,respectively,with the reduce of irrigation by one time.When the N application amount of summer maize was130-180 kg/hm²,the yield will reduce by 12,36,59,83 and 106 kg/hm²,respectively,and the N emission intensity will decrease by 2.3,1.7,1.1,0.4 and 0.1 kg N/hm²,respectively,with the decrease of N input by an increment of 10 kg/hm².When the irrigation times reduced from twice to zero,the yield will reduce 296,1425 kg/hm²,and the N emission intensity will reduce 1.1 and 1.0 kg N/hm² respectively.In conclusion,the emission of farmland nitrogen could be reduced while grain yiled being increased through the optimization of management scheme during crop production by reducing N application rate and irrigation times to certain extent,or by changing crop planting patterns.