Effect Of The Application Of Biochar On Carbon Sequestration Of Aggragates In Red-yellow Soils

As the basis of agricultural production,cultivated land is an important resource to ensure human eating and national food security.However,people ’s long-term highintensity use of cultivated land and the contradiction between economic development and cultivated land protection have greatly reduced high-quality cultivated land resources.There is an urgent need for high-quality new cultivated land to maintain sustainable agricultural development and alleviate the severe agricultural production situation.As a high-quality soil amendment,biochar has many characteristics such as high p H value,porosity,and high carbon-nitrogen ratio.After being applied to soil,it can effectively increase soil p H value,improve soil structure,repair contaminated soil,and fix carbon and reduce emissions.It has received more and more attention in the field of agricultural environmental research.In this paper,the newly reclaimed red and yellow soil cultivated land was taken as the research object.Firstly,the effects of corn straw biochar,rice straw biochar and pig manure biochar on soil physical and chemical properties and aggregate size distribution under different application rates(0,0.75 %,2.25 %)were studied.Secondly,the distribution and carbon and nitrogen contents of heavy fraction and different combined humus in water-stable aggregates with different particle sizes under different treatments were analyzed,and the effects of different biochar application on the stability of soil aggregates with different particle sizes were explored.Finally,the different forms of iron-aluminum oxides and their respective combined organic carbon were further extracted,and the effects of different biochar applications on the mechanism of iron-aluminum oxide cementing organic carbon in aggregates with different particle sizes were discussed,and the dynamic relationship between each cementing material was analyzed.Based on this,the effects of different biochar applications on the carbon sequestration mechanism of red-yellow soil aggregates were explored,and the optimal biochar type and application amount for improving the newly reclaimed red-yellow soil were clarified,which provided a theoretical basis for improving the fertility of newly reclaimed red-yellow soil and maintaining high-quality sustainable development.The main results are as follows :(1)Compared with the control,the application of different types of biochar increased the soil p H value,and the application of biochar effectively increased the soil total nitrogen,organic carbon and total phosphorus content.Single application of chemical fertilizer and different biochar under different application rates had no significant effect on the particle size distribution of red and yellow soil aggregates.Compared with the control,different biochar application treatments had a significant improvement effect on the content of organic carbon and total nitrogen in soil aggregates of each particle size.The total nitrogen and organic carbon in the soil mainly existed in > 0.25 mm soil aggregates,and the contribution rate of both was above 50 %.All treatments increased the soil C / N ratio compared with the control,and the C / N ratio between the same biochar treatments increased with the increase of application rate.The application of biochar will increase the total phosphorus content in the aggregates of each particle size,but the effect on the total potassium content is not obvious.(2)The application of different biochars effectively increased the content of heavy fraction organic carbon and total nitrogen in soil aggregates of different particle sizes,and the treatment of 2.25 % pig manure biochar had the best effect on the improvement of the two.In the particle sizes of > 0.25 mm and 0.25-0.053 mm,the application of different biochars increased the C/N ratio of the soil and heavy fraction compared with the control,and the heavy fraction C/N ratio was significantly higher than the soil C/N ratio.Compared with the control,the application of different biochar significantly increased the content of loosely,stably and tightly combined humus in aggregates of each particle size,and the effect of 2.25 % application of corn straw biochar was the most obvious.Under the same particle size aggregates,the content of tightly combined humus was the highest,followed by loosely combined humus,and the content of stably combined humus was the least.The content of loosely,stably and tightly combined humus in < 0.053 mm aggregates was the highest in all particle sizes.(3)The content of iron and aluminum oxides in the same particle size aggregates treated with biochar showed free iron and aluminum oxides > amorphous iron and aluminum oxides > complexed iron and aluminum oxides.Compared with the control,the 2.25 % application rate of biochar reduced the content of free iron and aluminum oxide in the aggregates of each particle size.The 0.75 % application rate of pig manure biochar and the 2.25 % application rate of corn straw biochar had a reduction effect on the content of amorphous iron and aluminum oxide.Under the condition of 0.75 %application rate,different types of biochar increased the content of complex iron and aluminum oxide(except pig manure biochar treatment).Compared with the control,all biochar treatments significantly increased the content of complex iron-aluminum oxide-bound organic carbon in aggregates of different particle sizes.In > 0.25 mm aggregates,0.75 % application of different types of biochar increased the content of amorphous iron-aluminum oxide-bound organic carbon,while 2.25 % application treatment was the opposite.The content of complexed iron-aluminum oxide bound organic carbon aggregates in each particle size is 0.25 mm and 0.25-0.053 mm,respectively.In the same particle size,the bound organic carbon content of complex iron-aluminum oxide > the bound organic carbon content of crystalline iron-aluminum oxide > the bound organic carbon content of amorphous iron-aluminum oxide.(4)There was no correlation between the physical and chemical properties of soil aggregates,the distribution of heavy fraction carbon and nitrogen,and the different combined humus and the particle size distribution of soil aggregates.Soil organic carbon content was significantly correlated with the contents of different bound humus in aggregates <0.053 mm in size,but the correlation between soil organic carbon content and compact,stable and loose bound humus content in aggregates >0.25 mm in size decreased gradually,and no correlation was found in aggregates between 0.25 and 0.053 mm in size.There was a significant or extremely significant positive correlation between the content of recombinant organic carbon and the content of loose,stable and tightly bound humus in the aggregates with particle size >0.25 mm and<0.053 mm.The increase of organic carbon in the original soil promoted the cementation of complex organic carbon in the aggregates of >0.25 mm and <0.053 mm.The free ferric oxide and aluminum transform to other forms and promote the increase of the content of hravy fraction organic carbon.