Effects Of Maize Stover Biochar On Soil Carbon Pool Activity And C-budget Of Brown Earth

The increasing CO₂ emissions are believed to be the main cause of global climate change,and excessive greenhouse gases emissions will put the earth's ecosystem in an environment of continuous and drastic change,which is dangerous and difficult to reverse.Besides,agriculture,forestry and other land utilization types have become the second largest source of greenhouse gas emissions of the world,and improving soil carbon sequestration has become an important means to reduce agricultural greenhouse gas emissions.Northeast China is one of the three golden maize belts in the world,and it is an important grain producing area as well.A large amount of stover produced every year can not be directly returned to the field,which leads to the exploration of the technology of biochar returning to the field.The long-term effects of the two stover returning ways on the transformation of soil carbon sink components and carbon budget are not well studied.In this study,based on a long-term of brown soil with biochar trial platform,five consecutive years?2013-2017?experiment was carried out to investigate the carbon turnover of soil-crop systems under different stover returning ways and different application amount of biochar.This study is to provide the scientific basis and support for the carbon emissions reduction technology centering on biochar.The specific research contents and results are as follows:1.Effects of different stover returning approaches on soil physical and chemical propertiesBefore sowing in each maize growing season,the maize stover and its derived biochar were returned to the field respectively,and the amount of the maize stover and biochar returned to the field were 7.5 t�hm^-2 and 2.63 t�hm^-2.The five-year average shows that both stover and biochar returning can significantly improve soil p H value,porosity and lower soil bulk density,and there is no significant difference between the two treatments.In addition,both stover and biochar returning significantly increased the content of available potassium and total phosphorus in soil,but had no significant effect on the content of available nitrogen,available phosphorus and total potassium in soil.Only stover returning significantly increased soil total nitrogen content compared with the control,but there was no significant difference compared with biochar returning.2.Effects of miaze stover and its derived biochar on soil greenhouse gas emissions and carbon budget of farmland ecosystem.Both stover and its biochar returning significantly increased soil CO₂ emissions,but the soil CO₂ emissions under biochar treatment were significantly lower than that under direct stover returning treatment.These two treatments significantly reduced soil N₂O emissions,and the soil N₂O emissions under biochar treatment were significantly lower than that under stover returning.The stover and its biochar returning both significantly increased the amount of CH₄ absorbed by the soil,and the CH₄ absorption of stover returning was significantly higher than that of biochar treatment.In addition,both of them significantly reduced the global warming potential?GWP?of N₂O and CH₄,and the biochar returning was significantly lower than stover returning.The greenhouse gas emission intensity?GHGI?of N₂O and CH₄ under the biochar treatment was the lowest.The net C gains of biochar treatment was significantly higher than that of stover treatment.3.Response of soil labile organic carbon fractions to stover and its derived biochar returning.Both stover and biochar returning not only significantly increased the content of soil organic carbon?SOC? and dissolved organic carbon?DOC?,easily oxidizable organic carbon?EOC?,particulate organic carbon?POC?,light fraction organic carbon?LFOC?,and microbial biomass carbon?MBC?,but also improved the ratio of the labile organic carbon fractions to SOC.The biochar treatment was significantly higher than that of stover returning only on LFOC contents and LFOC/SOC,and stover returning for the other indexes above was significantly higher than that of biochar returning.In addition to DOC/SOC values,soil CO₂ emissions were significantly positively correlated with SOC,soil labile organic carbon fractions and their ratios to SOC.After five consecutive years of returning,both stover and its derived biochar returning significantly increased the carbon reserves of soil 0-60 cm compared with the control,besides,there was no significant difference between the stover and biochar treatments.4.Effects of different application amounts of biochar on soil labile organic carbon and carbon pool management index?CPMI?Before the start of the experiment,different amounts of biochar were applied at one time.The application amounts of biochar were 15.75 t�hm^-2?BC1?,31.5 t�hm^-2?BC2? and 47.25 t�hm^-2?BC3?,respectively.Under different biochar application rates,the contents of SOC,EOC,MBC,POC and LFOC were significantly increased in each biochar treatment.Only DOC contents decreased with the increase of biochar application rate.The application of biochar significantly increased the CPMI of maize field.All biochar treatments not only increased the contents of SOC and EOC,but also increased the contents of non-labile organic carbon?NLC?,and NLC increased significantly with the increase of the amount of biochar.This indicated that biochar could not only improve the quantity and quality of soil organic matter,but also increase the content of soil stable organic carbon.In other words,biochar could improve soil quality and increase soil carbon sequestration at same time.5.Different application rates of biochar had different effects on the content of soil aggregates after five years of continuous planting of maize.BC2 treatment significantly increased the aggregate content of particle size>2 mm.BC3 treatment significantly increased the content of 2-0.25 mm aggregates,and all biochar treatments had no significant effect on 0.25-0.053 mm aggregates.In addition,biochar treatments significantly reduced the contents of free particles in soil.Biochar application could significantly improve the stability of soil aggregates,among which BC2 treatment had the highest stability.The effects of different application rates of biochar on the organic carbon content of aggregates were different.Only BC3 treatment significantly increased the organic carbon contents of all size aggregates.The relative contribution rate of soil organic carbon in 2-0.25 mm soil aggregates was the highest.Moreover,the relative contribution rate of soil organic carbon in<0.053 mm particle size decreased with the increase of biochar application rate.