Impacts Of Fertilizer On Greenhouse Gas Emissions And Yield Of Maize Farmland

To determine the suitable nitrogen（N）fertilizer rates and the ideal proportion of organic fertilizer combined with chemical fertilizer for summer maize in the black soil area.Two experiments were established to study the effects of fertilization on summer maize yield,nitrogen uptake and greenhouse gas emissions of summer maize in black soil area.Experiment one was the nitrogen fertilizer dosage test.Four nitrogen application rates were set in the summer maize growth period of 2018 and2019: CK（no fertilization）,N180（180 kg N·hm-2）,N270（270 kg N·hm-2）,N360（360kg N·hm-2）.The maize yield,biomass,root characteristics,plant nitrogen accumulation,soil ammonium nitrogen,nitrate nitrogen and N₂O and CO2 emission of maize were measured.The second experiment was the ratio test of organic and inorganic application under the condition of equal nitrogen.In the growth period of summer maize in 2018 and 2019,different organic and inorganic application ratios were set,respectively: 100% inorganic fertilizer（inorganic fertilizer 270 kg N·hm-2,NPK）,organic fertilizer replacing 30% inorganic fertilizers（inorganic fertilizers 180 kg N·hm-2+90 kg pure N organic fertilizer,NPKM30）and organic fertilizer replacing 50%inorganic fertilizers（inorganic fertilizers 135 kg N·hm-2+135 kg pure N organic fertilizer,NPKM50）and CK（no fertilizer input）.The yield,biomass,root characteristics,plant nitrogen accumulation,soil ammonium nitrogen,nitrate nitrogen content of maize were measured.The N₂O and CO2 emissions were determined by static box-gas chromatography.Understanding the effects of N application rate and Organic and inorganic application on soil greenhouse gas emission and yield under the same N fertilizer input,could supplied the theoretical basis and technical support for reasonable fertilization,keeping crop yield stable,reducing fertilizer input and nitrogen（N）loss,reducing environment pollution.The main research results were as follows: Increasing nitrogen application significantly increased maize yield.The maximum grain yield was 10378.5 kg·hm-2when N application rate was 270 kg·km-2,and the yield decreased by 2.04% when N application rate was more than 270 kg·hm-2.Compared with the CK,the average maize yield for the NPK,NPKM30 and NPKM50 increased by 43.97%,50.77% and 43.64,there was no significant difference of maize grain yield among NPK,NPKM30 and NPKM50 under the condition of equal N fertilizer input.During the periods of maize growth,soil N₂O flux showed dynamic changes,and fertilizer input increased the greater the peak.Compared with the CK,the average accumulation N₂O emission of the three treatments N180,N270 and N360 of increased by 1.74%,38.23% and 77.89%.The N₂O emission response to increased N input is linear in the range of 0²70 kg·hm-2,but nonlinear in the range of more than 270 kg·hm-2.The cumulative N₂O emission of N360 treatment was 1.29 times that of N270 treatment.Compared with the NPK,the N₂O cumulative emission increased by 6.03%for the NPKM30 treatment,however reduced by 8.33% for the NPKM50.During the periods of maize growth soil CO2 flux showed similar temporal patterns among three treatments,the average CO2 flux for the two years ranged from 74.53 to 367.04 mg·m-2·h-1.Fertilization input significantly increased the cumulative CO2 emission,and the cumulative CO2 emission of organic fertilizer treatment was higher than that of chemical fertilizer treatment alone,and increased with the increase of organic fertilizer application.With the increase of nitrogen application rate,CO2 emission and Global Warming Potential（GWP）increased firstly and then decreased.Compared with CK,the average cumulative CO2 emission for the N180,N270 and N360 increased by 2.82%,21.63% and 8.87%;Global warming potential（GWP）increased by 4.77%,28.15% and 22.52%;However,the greenhouse gas emission intensity（GHGI）reduced by 22.93%,16.66% and 18.02%.Compared with the NPK treatment,the average CO2 accumulation increased by 0.92% and 5.88%.The GWP of organic fertilizer treatment was higher than that of chemical fertilizer treatment alone,However,the GHGI decreased by 2.55% for the NPKM30 treatment and increased by2.16% for the NPKM50 treatment compared with NPK.The results of correlation analysis showed that the yield with biomass,root nitrogen accumulation,aboveground nitrogen accumulation,rhizosphere soil NO₃^--N and INN content and non-rhizosphere soil NH₄⁺-N,NO₃^--N and INN content of summer maize had significant positive correlation,GWP with N₂O,CO2 cumulative emission had significant positive correlation,and GWP with non-rhizosphere soil NO₃^--N and INN content significant negative correlation.These results showed: In a certain range,maize grain yield,greenhouse gas emissions and global warming potential increased with the increase of N application rate,but when N application rate was 360 kg·km-2,maize grain yield and global warming potential did not increase,but decreased.Under the condition of constant nitrogen amount,the suitable organic fertilizer combined with chemical nitrogen fertilizer could keep maize yield stable,increase plant biomass and N accumulation,meanwhile reduce greenhouse gas emission intensity.Considering the maize yield,the economic benefit of nitrogen fertilizer and the ecological benefits of greenhouse gas emissions in the black soil area,it is considered that organic fertilizer replacing 30%inorganic fertilizers is the best proportion to achieve keep maize yield stable,reduce N fertilizer input and decreased emission.