Effects Of Nitrogen-Saving Mode Of Maize-Soybean Intercropping On Crop Growth And Greenhouse Gas Emission In Farmland

The use of synthetic nitrogen fertilizer has greatly improved food production and alleviated the global food shortage.However,the excessive use of nitrogen fertilizer has a serious impact on the nitrogen cycle balance of agricultural ecosystem,resulting in soil compaction,soil fertility decline,excessive greenhouse gas emissions in farmland,and certain damage to the environment.Maize-soybean intercropping is a green planting mode that can not only reduce weight and medicine,but also fix nitrogen and reduce emissions.Based on this,this study took maize-soybean intercropping as the research object,and set four treatments in 2020 and 2021:monoculture of maize,monoculture of soybean,maize-soybean intercropping,and maize-soybean intercropping to save nitrogen.The static dark box/gas chromatography was used to monitor the whole growth season,and the effects of maize-soybean intercropping nitrogen saving mode on crop growth,greenhouse gas emission in farmland,and the variation law of soil physical and chemical properties were analyzed,aiming to explore the optimal nitrogen application rate under maize-soybean intercropping mode without reducing yield.The results are as follows:（1）The photosynthetic characteristics and aboveground dry matter accumulation of maize-soybean intercropping were significantly higher than those of monoculture maize.The nitrogen accumulation in the upper part of corn field of maize-soybean intercropping at harvest stage was 5.28%–11.17%higher than that of maize-soybean intercropping with nitrogen-saving treatment,while the dry matter of soybean under maize-soybean intercropping with nitrogen-saving treatment at harvest stage was 2.49%–3.67%higher than that of maize-soybean intercropping with nitrogen-saving treatment.The land equivalent ratios of intercropping treatments were 1.1-1.21,and the actual yield loss indexes of soybean and maize were all greater than 0.The occupation forces of intercropping maize and soybean were 0.08and-0.08,respectively.The occupation forces of intercropping maize and soybean were 0.07and-0.07,respectively.In the two years,the partial productivity of nitrogen fertilizer in the intercropping treatment was 18.50%-26.10%higher than that in the intercropping treatment.（2）From the perspective of greenhouse gas emissions,the cumulative emissions of N₂O and CO₂ of maize monoculture were higher than those of maize-soybean intercropping.The cumulative emissions of N₂O of maize monoculture were 4.9%–7.45%higher than those of maize-soybean intercropping.The cumulative emissions of CO₂ of maize monoculture were2.7%–10.28%higher than those of maize-soybean intercropping.The cumulative emissions of N₂O of maize-soybean intercropping were 14.42%–14.57%higher than those of maize-soybean intercropping.The cumulative CO₂ emission of maize-soybean intercropping was1.43%–1.59%higher than that of maize-soybean intercropping.The global warming potential of monoculture maize was 5.94%–11.42%higher than that of maize-soybean intercropping,5.78%–9.25%higher than that of maize-soybean intercropping,and 2.01%–2.79%higher than that of maize-soybean intercropping.In terms of soil physical and chemical properties,the contents of nitrate nitrogen,ammonium nitrogen and total nitrogen in maize-soybean intercropping were higher than those in maize-soybean intercropping.The content of total nitrogen in maize-soybean intercropping was 24.72%–26.1%higher than that in maize-soybean intercropping.（3）From the perspective of yield and economic benefits,the average yield of maize-soybean intercropping and maize-soybean intercropping nitrogen-saving treatments in the two years reached 65.37%and 62.85%of the yield of single maize,respectively,and the average yield of soybean reached 50.88%and 49.27%of the yield of single soybean,respectively.The maize yield of maize-soybean intercropping was 2.34%–5.73%higher than that of maize-soybean intercropping nitrogen-saving treatment,and the soybean yield of maize-soybean intercropping was 8.71%higher than that of maize-soybean intercropping nitrogen-saving treatment in 2020.The soybean yield of maize-soybean intercropping was 1.92%higher than maize-soybean intercropping in 2021.The ear weight,ear length,ear diameter,grain number per row,row number per ear and 100-grain weight of intercropping maize were higher than those of monoculture maize.There was no significant difference in grain number per plant,pod number per plant and 100-grain weight between intercropping soybean and monoculture soybean.The total income and net income of each treatment in two years were:maize-soybean intercropping was higher than that of maize-soybean intercropping was higher than that monoculture maize was higher than that monoculture soybean.There were significant differences in nitrogen content of maize grain in two years.The nitrogen content of soybean grain was significantly higher than that of maize grain.In summary,the tillage measures of maize-soybean intercropping nitrogen-saving mode(N:150 kg hm^–2)in this study can make greater use of the complementarity and coordination of the two crops under the condition of appropriate reduction of nitrogen fertilizer,which can not only improve the utilization rate of light and heat resources,improve the system yield,but also reduce the greenhouse gas emissions in farmland.It is a better planting method in this study.