Effects Of Biochar On Soil Organic Carbon Components And Humic Acid Structural Characteristics In Black Soil

Soil organic carbon plays an important role in soil fertility and is also a significant index to evaluate soil quality.The application of biochar is an effective measure to increase soil organic carbon storage and improve soil fertility.In order to explore the impact of biochar on the fraction and quality of soil organic carbon,this experiment took the black soil area of Northeast China as the research object,and added the same amount(7500 kg hm^-2)of different kinds of biochar:Rice husk biochar（P1）;Corn stalk biochar（P2）;Tobacco stalk biochar（P3）.The effects of different kinds of biochar on the soil physical and chemical properties,content of soil active organic carbon,aggregate organic carbon and humus carbon were compared,and the chemical structure of humic acid was analyzed spectroscopically to clarify the turnover characteristics,quantity and quality changes of soil organic carbon under the treatment of different kinds of biochar.The main research results are as follows:（1）Rice husk,corn stalk,and tobacco stalk biochar significantly increased soil moisture content during the tobacco harvest by 13.00%,6.62%,and 5.21%,respectively.The tobacco stalk biochar significantly increased soil p H from 6.01 to 6.48.At the same time,soil organic carbon content was significantly increased by 5.85 g·kg^-1 compared with no biochar treatment.The C/N ratio increased by 42.34%.（2）The addition of biochar significantly increased the soil active organic carbon content.Compared with no biochar treatment,rice husk and tobacco stalk biochar increased the soil microbial biomass carbon by 31.99%and 33.68%,and the readily oxidizable organic carbon was increased by 34.81%and 22.78%,respectively.In addition,rice husk biochar treatment significantly increased soil particle organic carbon content by 33.48%.The proportion of particulate organic carbon in soil organic carbon reached 7.01%to 8.69%,and the contribution to soil organic carbon was greater.Microbial biomass carbon and readily oxidizable organic carbon have a high sensitivity index.（3）Biochar improved soil aggregate structure and increased the content of 1-2mm granular aggregates.Corn stalk biochar had the best effect,and the stability of soil aggregates was the highest.Compared with no biochar application,the proportion of micro-aggregates decreased significantly,and the content of<0.25mm granular aggregates decreased by 14.28%,under the tobacco stalk biochar treatment.Rice husk and tobacco stalk biochar increased the organic carbon content of>2mm grain size aggregates by 6.50 g·kg^-1 and 7.40 g·kg^-1,respectively,while corn straw and tobacco stalk biochar increased the organic carbon content of 0.25～0.5 mm grain size aggregates by 53.24%and 30.81%.All treatments had no significant effect on the organic carbon content of micro-aggregates<0.25mm.Tobacco stalk biochar significantly increased the contribution rate of organic carbon in granular aggregates of0.25～0.5mm and 1～2mm,while corn stalk biochar significantly increased the contribution rate of organic carbon in granular aggregates of 1～2mm.（4）Biochar had no significant effect on humus carbon content.Compared with no biochar application,the humic acid carbon content increased significantly by 23.5%under the rice husk and tobacco stalk biochar treatment.The application of rice husk biochar also significantly promoted humin carbon accumulation,increasing by 66.88%.Under tobacco stalk biochar treatment,the content of fulvic acid carbon reduced,and the ratio of HA/FA increased significantly by 37.93%.（5）According to FTIR and ¹³C-NMR spectral analysis,the application of biochar changed the chemical structure of soil humic acid.Compared with no biochar application,the Aliphatic C/Aromatic C of tobacco stalk biochar treatment increased significantly by 25%,which enhanced the aliphatic property of humic acid molecules,weakened the aromatic property and simplified the structure;Tobacco stalk biochar also increased the Hydrophobic C/Hydrophilic C of humic acid by 35.16%.To sum up,different kinds of biochar have different effects on soil organic carbon composition due to their different structures and properties.In the short term,biochar can improve soil physical and chemical properties and supplement soil carbon.Rice husk biochar is superior in stimulating soil organic carbon activity.Corn stalk biochar showed advantages in improving soil structure.Tobacco stalk biochar promoted the accumulation of organic carbon in black soil aggregates（especially in large aggregates）,enhanced the physical protection of aggregates,and performed well in soil humification process and carbon fixation.However,the application of tobacco stalk biochar simplified the molecular structure of soil humic acid,which tended to be an adverse effect.