Response Of Greenhouse Gases Emissions And Net Greenhouse Effect To Nutrient Management In Purple Soil

The massive emission of greenhouse gases caused by human activities has led to a series of major global environmental problems,such as climate change and global warming,and it is one of the main research topics on global changing.The farmland ecosystem is the most active part of human activities.As one of the most important sources of man-made greenhouse-gases emissions,the cropland soil is strongly influenced by agricultural management measures.Seeking reduction in greenhouse gas emission from the perspective of farmland management is an important direction of current research.Inputs and the application of chemical fertilizers have a great effect on the substantial increase of food production,but the excessive application of chemical fertilizers in the farmland ecosystem has brought worrying environmental problems.Nutrient management is an important factor affecting greenhouse gas emissions and also the most important part of farmland management.At present,there have been some reports on the greenhouse gas emission of purple soil,but they focuses mainly on the effect of different farming systems and methods,nitrogen fertilizer types,and mulching.Different nutrient management measures,especially the application of phosphate fertilizer,the interaction of nitrogen and phosphorus,and the application of calcium/sulfur fertilizer（Flue-gas desulfurization gypsum）on soil greenhouse gas emissions are scarce.The characteristics and generation mechanism of greenhouse gas emissions from agricultural sources in the purple soil area and the response mechanism of the net greenhouse effect to nutrient management are still unclear.Therefore,based on the long-term fertilization positioning test at the National Purple Soil Fertility Monitored Base in Beibei,Chongqing（selecting no fertilization（CK）,PK fertilization（PK）,N fertilization（N）,NP fertilization（NP）,NK fertilization（NK）,NPK fertilization（NPK））for purple soil rice-wheat rotation farmland ecosystems（cycling from May 2014 to May 2015）,and relying on the International Base for S&T Collaboration on Water Environmental Monitoring and Simulation in TGR Region in Fuling,Chongqing(setting 4 calcium/sulfur fertilizer（Flue-gas desulfurization gypsum）levels（P₁S₀ treatment:0 t/hm²,P₁S₂ treatment:2 t/hm²,P₁S₄ treatment:4 t/hm²,P₁S₈treatment:8 t/hm²）,4 phosphate fertilizer levels(P₀S₀ treatment:0 kg/hm²,P_0.5S₀ treatment:75 kg/hm²,P₁S₀ treatment:150 kg/hm²,P₂S₀ treatment:300 kg/hm²))for purple soil mustard-maize rotation farmland ecosystems（cycling from November 2015 to November 2016）,we takes the purple soil in the Three Gorges Reservoir area as the study object,using static chamber-based method,to conduct the annual scale of the soil-gas interface greenhouse gas（N₂O,CH₄,CO₂）exchange flux in-situ dynamic monitoring research.Through field in-situ monitoring test of greenhouse gas emissions from purple soils under different crop rotation systems,to determine the system’s greenhouse gas emissions and net greenhouse effect,discuss its emission rules,generation mechanisms and main control factors,and further clarify the response mechanism of greenhouse gas emissions to the nutrients management under different crop rotation systems and also the estimation of the N₂O emission coefficient applicable to the purple soil area related to chemical fertilizer application,can not only improve the carbon/nitrogen cycle research of the purple soil farmland ecosystem,but also reduce the greenhouse gas emission of the farmland in the purple soil area.Nutrient management measures provide scientific reference and theoretical basis,which have important practical significance for China’s agricultural cost-saving and efficiency-increasing,energy-saving and emission reduction,and also the establishment of a regional greenhouse gas emission inventory.The main research conclusions of the thesis are as follows:（1）Effects of Balanced Fertilization on Greenhouse Gas Emissions from Purple Soil in Rice and Wheat RotationDuring the entire test monitoring period,soil N₂O,CH₄,and CO₂ emissions had certain seasonal variation characteristics.The emission of N₂O fluctuated significantly in the wheat season,and an emission peak appeared after fertilization.However,in the rice and fallow season,all treatments were subjected to soil moisture and fluctuated at a low level.CH₄ emission peaks appeared after fertilization in the rice season,and the emission rate fluctuated greatly in the rice season,which was considered as a large CH₄ emission source.However,the fallow and wheat season remained at a weak rate for a long time.Each treatment alternately becomes CH₄ small source or small sink.The seasonal change trend of CO₂ was more consistent with temperature.Except for the relatively stable in the early and middle of winter wheat growth,the fluctuation was more obvious in other time ranges.Nitrogen fertilizer treatments increased the cumulative emissions of soil N₂O,CO₂,and CH₄.The cumulative N₂O emissions of phosphate fertilizer treatments were lower than those without phosphate fertilizer treatment.Applying phosphate fertilizer treatments increased the cumulative CH₄ emission compared with no phosphate fertilizer treatment in the rice and fallow season,but the cumulative CH₄emissions of phosphate fertilizer treatments in the wheat season were lower than those without phosphate fertilizer treatment.At the same time,the cumulative CO₂ emissions of phosphate fertilizer treatment were higher in the rice,fallow and wheat season than the treatment without phosphate fertilizer.So,it showed that phosphorus application can promote CO₂ release.Compared with the application of phosphorus or potassium fertilizer alone,the combined application of phosphorus and potassium fertilizer suppressed N₂O emissions in the rice,fallow and wheat season.Moreover,the combined application of nitrogen and phosphate fertilizer stimulated CH₄emissions in the rice and fallow seasons,but suppressed CH₄ emissions in the wheat season.Compared with the separate application of nitrogen or phosphate fertilizers,combined application of nitrogen and phosphate fertilizer stimulated CO₂ emissions in the rice and wheat seasons,but suppressed CO₂ emissions in the fallow season.According to the annual monitoring period,N₂O emissions from different treatment were mainly affected by temperature,soil moisture,NO₃^-（P<0.01）and available phosphorus（P<0.05）.CH₄ emission was mainly affected by temperature,soil moisture,p H value,NO₃^-,available phosphorus（P<0.01）.CO₂ emissions was mainly affected by temperature,soil NH₄⁺（P<0.01）and NO₃^-（P<0.05）.Compared with no nitrogen fertilizer,applying nitrogen fertilizer increased soil NH₄⁺,NO₃^-content and reduced soil available phosphorus content,and the mixed application of nitrogen and phosphorus fertilizers was more conducive to the absorption and utilization of soil phosphorus by crops.Compared with no phosphate fertilizer,applying phosphorus increased the soil available phosphorus content,while reducing soil NH₄⁺,NO₃^-content.（2）Effects of Balanced Fertilization on the Net Greenhouse Effect of Purple Soil in Rice and Wheat RotationThe balanced fertilization promoted the improvement of nitrogen fertilizer agronomic utilization,but also improved the N₂O emission coefficient to a certain extent.At the same time,balanced fertilization promoted the increase of crop yield and income compared with partial application of chemical fertilizers,and the effect of nitrogen fertilizer was better than that of phosphate fertilizer.Among different treatments,NPK performed the best among all three indicators.Through the literature analysis method,compared with the research on N₂O emission in various places before July 2020,it can be seen that the results of calculating the N₂O emission coefficient with CK,PK,P,and K fertilizer treatments as the control of nitrogen-free treatments are quite different,which will bring great uncertainty to the estimation of N₂O emissions.In terms of NECB’s interannual value,all treatments appear to be a net source of atmospheric CO₂,of which the contribution of wheat season was 54.33-83.51%.Except for the CK in the rice season,the remaining NECB contribution almost all came from the fallow season.During the monitoring period throughout the year,the Net GWP for different treatments was between9798.71-14178.40 kg CO₂-eq/hm².The wheat season contributes 43-60%,coupled with the fallow period,this proportion was further increased to 65-85%.According to the annual monitoring period,the GHGI of each treatment was between 0.93-2.72 kg CO₂-eq/kg grain.Among the treatments,the GHGI of NPK was the lowest.（3）Effects of Phosphorus and Calcium/Sulfur（Flue-gas desulfurization gypsum）Input on Greenhouse Gas Emissions from Purple Soil in Maize and Mustard Rotation SystemThe N₂O emission rate of each treatment fluctuated slightly in the mustard,fallow season,but more obviously in the maize season,and the emission peaks appeared after fertilization.The fluctuation of CH₄ emissions from different treatments throughout the year were not obvious.The CO₂ emission rate was higher in spring and summer,and lower in autumn and winter.The fluctuation range of CO₂ emission of each treatment was relatively small in the mustard and fallow season but larger in the maize season,and the emission peaks also appeared after fertilization.As far as the annual monitoring period was concerned,P_0.5S₀ promoted N₂O emissions,while P₂S₀ and P₁S₀ suppressed N₂O emissions.And it can be seen that the addition of FGDG significantly inhibited the cumulative N₂O emission.The treatment of phosphate fertilizer promoted CH₄emission compared with the control,but the more phosphate fertilizer was applied,the less obvious the promotion effect.The addition of FGDG treatment significantly inhibited soil CH₄ emissions.The cumulative CO₂ emissions of different phosphate fertilizer treatments were increased compared with the P₀S₀,indicating that phosphate fertilizer application significantly promoted CO₂ emissions.With the increase of the amount of FGDG added,the CO₂ emission has changed from promoting to inhibiting.According to the annual monitoring period,the N₂O emissions from different treatment was mainly affected by temperature,soil moisture,water-soluble Ca²⁺,NH₄⁺,NO₃^-（P<0.01）and water-soluble SO₄^2-,available phosphorus（P<0.05）.CH₄ emissions was mainly affected by temperature,soil NO₃^-,NH₄⁺,water-soluble Ca²⁺,SO₄^2-（P<0.01）and NO₃^-（P<0.05）.CO₂ emissions was mainly affected by temperature,soil NH₄⁺（P<0.01）and water-soluble Ca²⁺,SO₄^2-,NO₃^-（P<0.05）.（4）Effect of Phosphorus and Calcium/Sulfur（Flue-gas desulfurization gypsum）Input on the Net Greenhouse Effect of Purple Soil in Maize and Mustard Rotation SystemCompared with CK,the different fertilization treatments all showed an increase in yield.In the whole year,for different phosphate fertilizer treatments,a reasonable constant phosphate fertilization was more conducive to improving the nitrogen fertilizer agronomic utilization and increasing crop yield than the treatment of reducing and increasing phosphorus.Except for the P₁S₀ in the mustard season,the application of FGDG reduced crop nitrogen fertilizer agronomic utilization.In addition to the P₁S₂ which showed an increase in crop yield,the other two high FGDG treatments showed a decrease in crop yield for the whole year.The variation range of the total N₂O emission coefficient for each treatment in the two seasons was between 0.25-11.77%,with an average value of 3%,which was generally decreased with the increase of amount of phosphate fertilizer and FGDG.The NECB values of the treated soils were all negative,which were considered as a net source of atmospheric CO₂.Generally speaking,in terms of the whole year,phosphate fertilizer and FGDG application reduced the system NECB value.The contribution of different components to Net GWP were in the same order in crop growing season and fallow season,which was NECB>R_N2O>R_CH4.The Net GWP during the whole year was between 7813.32-19218.18 kg CO₂-eq/hm².Generally speaking,the application of phosphate fertilizer increased and the FGDG treatments decreased the net GWP value of the system.The GHGI during the whole year ranged from 0.54 to 1.88 kg CO₂-eq/kg grain.The application of phosphorus fertilizer increased system GHGI,and with the increase of the amount of FGDG,GHGI showed a trend of first increasing and then decreasing.P₁S₄ performed best among all the FGDG treatments.