Effects Of Straw Input And Nitrogen Fertilizer On Greenhouse Gas Emissions From Farmland

The large emissions of greenhouse gas are the main causes of global warming and a range of environmental problems,and agriculture is an important source of greenhouse gas emissions.It is of great significance to mitigate climate change and the sustainable development of agriculture that to use effective measures to reduce greenhouse gas emissions in the process of agricultural production.Straw input is a key measure for improving soil quality,it can boost soil carbon sequestration capacity to mitigate climate change.In order to further clarify the impacts of straw input combined with other farmland management practices on soil properties,crop productivity and greenhouse gas emissions,this study was based on323 literatures data published before 2021 on greenhouse gas emissions and soil properties changes from farmland under straw input,using the meta-analysis method,obtained the effects of greenhouse gas emissions and soil properties changes under straw input and the interaction between straw input and other farmland management practices,and a long-term positioning experiment in wheat-maize rotation system in the Guanzhong Plain（started from 2003）was selected to carry out field observations.Two straw management measures（F:straw mulching,C:no straw mulching）,three fertilizer application rates[no fertilizer（N0）,120 kg N·ha^-1（N120）,240 kg N·ha^-1（N240）]and one fallow district（CK,no planting of any crops）were conducted in this study,with a total of seven treatments,which were recorded as CKN0,CN0,CN120,CN240,FN0,FN120 and FN240.A two-year field experiments were conducted in2019-2021 to assess the effects of long-term straw mulching and fertilization on soil properties and greenhouse gas emissions.The main results are as follows:1.Study on the effects of straw input on soil properties and comprehensive warming effect based on meta-analysis（1）Overall,straw input improved crop agronomic features,increased soil nutrient content,lowered soil bulk density,and had no influence on soil p H when compared to no straw input.Straw application rate and experimental period are the key factors affecting soil properties.Straw input boosted considerably crop yield by 8.86%and soil carbon storage by 12.8%,with no-tillage and upland fields benefiting the most from straw input.Furthermore,straw input boosted nitrogen use efficiency by 22.2%and water use efficiency by 23%,respectively.（2）Straw input increased CO₂,CH₄,and N₂O emissions by 24.8%,79.3%,and 28.3%,respectively.Under straw input,global warming potential（GWP）and greenhouse emission intensity（GHGI）increased,whereas net global warming potential（NGWP）decreased.Adopting appropriate agricultural management strategies,such as low straw application rate(<4.5 t·ha^-1),straw mulching,long-term straw input（Y≥5 years）,and no-tillage can minimize greenhouse gas emissions and produce lower GWP.The GWP and GHGI were also shown to be highly related to area-scaled CH₄ emissions,but the correlation with N₂O emissions was minor.Reasonable straw incorporation（such as straw application during the non-rice season）is the most important measure for reducing CH₄ emissions in paddy-upland fields.2.Effects of long-term straw mulching and fertilization on soil properties,crop yields and greenhouse gas emissions.（1）Whether straw mulching or not,long-term fertilization increased the content of soil total nitrogen,nitrate nitrogen,microbial biomass carbon and nitrogen,improved the activities of soil sucrase,cellulase and urease in the topsoil at maize harvest period,and reduced the content of ammonium nitrogen,while high fertilization level significantly reduced the soil p H and soil sucrase and cellulase activities.Compared with no straw mulching,straw mulching with the same fertilizer application rate increased soil organic carbon,total nitrogen,nitrate nitrogen,microbial biomass nitrogen content,increased significantly soil water content and urease activity in the topsoil at maize harvest period.Long-term fertilization increased significantly the yields of wheat and maize,but there was no significant difference in wheat and maize yields between N120 and N240 fertilization levels.Compared with no straw mulching,straw mulching with the same fertilizer application rate increased significantly maize yield,but had no significant effect on wheat yield.Correlation analysis showed that soil organic carbon content,total nitrogen content,nitrate nitrogen content,soil invertase activity,urease activity correlated positively with crops yield.（2）The wheat-maize rotation system in Guanzhong Plain is the emission source of CO₂and N₂O,the uptake sink of CH₄.Long-term fertilization and straw mulching increased the growth period cumulative emissions of CO₂.Whether straw mulching or not,high fertilizer application rate（N240）significantly increased the cumulative CH₄ emissions.Compared with CN0 treatment,the cumulative CH₄emissions of CN240 treatment increased by 38.73%-50%and 30.0%-43.07%in wheat and maize season,respectively;Compared with FN0 treatment,the cumulative CH₄emissions of FN240 treatment increased by 35.71%-61.14%and 29.34%-43.18%in wheat and maize season,respectively.Compared with no straw mulching,straw mulching with the same fertilizer application rate has no significant effect on the cumulative CH₄ emissions.The cumulative emissions of N₂O showed a pattern of high N fertilization and high release,and the N₂O emission flux was high about two weeks after fertilization.Compared with no straw mulching,straw mulching with the same fertilizer application rate had no significant effect on the cumulative N₂O emissions.Fertilization increased GWP and GHGI,compared with N120 treatment,N240 treatment significantly increased GWP by37.50%-146.87%and GHGI by 31.21%-174.33%,respectively.In general,under the same fertilizer application rate,straw mulching had no significant impact on GWP and GIGI compared with no straw mulching.In conclusion,an effective straw management practice coupled with appropriate farmland management measures has a great potential in mitigating greenhouse gas emissions on a long-term scale.The long-term experiment study showed that straw mulching combined with 120kg N·ha^-1 nitrogen fertilizer application rate is the best combination of crops,soil nutrients and environmental benefits,and is an excellent combination scheme for reducing greenhouse gas emissions and sustainable agricultural production in Guanzhong Plain.