Effects Of Nitrogen Reduction And Organic Fertilizer Instead Of Partial Chemical Fertilizer On Greenhouse Gas Emissions In Rice-rape Rotation

In recent years,the rapid increase of greenhouse gas concentration in the atmosphere has led to the rising global temperature.Climate warming has gradually become the focus of global attention.In addition to chemical combustion,agricultural emissions also have an important contribution to global warming.Nitrogen control is the most direct and effective measure to reduce agricultural greenhouse gas emissions.Therefore,it is important to study the low emission fertilization method on the premise of ensuring the output.Replacing part of chemical fertilizer with organic fertilizer can improve the yield of crops,but the application of organic fertilizer will also cause the increase of greenhouse gas emissions,so how to realize the scientific and reasonable utilization of organic fertilizer and how to reduce the greenhouse gas emissions in the process of returning farmland are the current research hotspot and focus.In order to explore Greenhouse gas emission characteristics of rice-rape rotation farmland were not clear and how to reduce greenhouse gas emissions and other important issues,a field experiment was conducted at Laisu town,Yongchuan District,Chongqing Municipality,in Southwest China,from 2018 to 2019.The study included six treatments:Nitrogen fertilizer（recorded as CK）,farmers’habit fertilization（recorded as FFP）,comprehensive nutrient management I（recorded as Z1）,comprehensive nutrient management II（recorded as Z2）,comprehensive nutrient management III（N reduction with bio-organic fertilizer substitution,Z3）,IV（N reduction with bio-organic fertilizer substitution and straw return substitution,Z4）,they were used to study the CH₄,CO₂,N₂O emission characteristics of rice-rape rotation under N reduction and organic substitution,and to estimate the global warming potential（GWP）and GHGI,the effects of environmental factors and soil physical and chemical properties on greenhouse gas emissions from farmland were analyzed,and the rational fertilization model of rice rape rotation system in Southwest China was discussed.The main results are as follows:1.The emission fluxes of three greenhouse gases in rice-rape rotation cropland showed obvious seasonal variation,and the seasonal variation patterns of three greenhouse gases under six treatments were similar.The greenhouse gas emissions of rice-rape rotation in Southwest China are mainly concentrated in CH₄,CO₂ and N₂O emissions of rice season and rape season.Compared with FFP treatment,nitrogen reduction and organic substitution significantly reduced the total emissions of CH₄,CO₂and N₂O in rice season,with the emission reduction effects of 23.2%-40.3%,25.4%-35.4%and 29.6%-31.3%respectively.2.The contribution of CH₄ and CO₂ to GWP was higher in rice-rape rotation farmland.The net contribution of CH₄ and CO₂ to GWP was 25.3%-46.3%and 31.2%-55.8%respectively.Compared with FFP treatment,the yield of rice and rape under nitrogen reduction and organic substitution did not change significantly,but GWP decreased significantly,which also led to the significant decrease of GHGI,with the decrease of20.6%-22.9%and 27.0%-37.8%respectively.3.The CH₄ and CO₂ emissions were positively correlated with the air temperature,the box temperature and the soil temperature（P<0.01）,N₂O emission flux had a significant positive correlation with soil temperature and box temperature and a significant negative correlation with precipitation（P<0.05）.CH₄ emission flux had a significant positive correlation with precipitation in rice and rape seasons（P<0.01）,but had no correlation in rice seasons,and CO₂ emission flux had no correlation with precipitation.Compared with FFP treatment,nitrogen reduction reduced CH₄,CO₂,N₂O emissions,organic substitution increased CH₄,CO₂ emissions,and reduced N₂O emissions.4.Compared with FFP treatment,Z4 treatment reduced CH₄,CO₂,N₂O cumulative emissions and GWP by 40.3%,25.4%,31.3%and 22.9%respectively,and Z4 treatment increased rice yield,but the yield effect was not significant.Considering the GWP and yield of rice-rape rotation,Z4 treatment was the best fertilization mode of rice oil vegetable rotation system in Southwest China.