Profile Difference Characteristics And Influencing Factors Of Organic Carbon Components In Typical Paddy Soil Under Long-term Fertilization

Aiming at the profile difference characteristics of organic carbon and its carbon components in typical paddy soil under long-term fertilization in Jiangxi Province,the difference characteristics of organic carbon chemical structure and the influencing factors of organic carbon components are not clear,this study takes the soil samples at the depth of0～100 cm from the national monitoring points in four counties of Jiangxi Province(Wannian in Shangrao,Shanggao in Yichun,Xingguo in Ganzhou,Jinxian in Nanchang)in2019 as the research object,to study the profile changes of organic carbon and its carbon components in typical paddy soils under long-term fertilization in Jiangxi Province,explore the impact of long-term fertilization on the stability of chemical structure of organic carbon,clarify the main sources of organic carbon,and quantify the main soil factors affecting the content of organic carbon components.The main results are as follows:(1)The organic carbon content in the profiles of Wannian,Shanggao,Xingguo and Jinxian national monitoring points is 6.26～29.06,2.58～21.80,3.38～22.18,2.15～23.03 g/kg,respectively.The organic carbon content in the lower layer(0～20 cm)of the conventional treatments at Wannian,Shanggao and Jinxian sites was significantly higher than the no-fertilizer treatment;there was no significant difference in the surface organic carbon content between the no-fertilizer and conventional treatments at the Xingguo site.The soil organic carbon content in the deep layer(20～100 cm)was significantly lower than that in the surface layer,and there was no significant difference in the organic carbon content between the 40～60,60～80,and 80～100 cm soil layers in the deep soil.This shows that the surface soil is greatly affected by agricultural management measures such as fertilization and long-term conventional fertilization treatment is more conducive to the accumulation of surface organic carbon.(2)Long-term conventional fertilization significantly increased the contents of dissolved organic carbon,potassium permanganate oxidizable carbon,non-labile organic carbon by 65.78%,10.21%～55.22% and 26.02%～46.21%,respectively;the contents of dissolved organic carbon,potassium permanganate oxidizable carbon in Jinxian point were significantly reduced by 75.43% and 34.89%,respectively,compared with the no-fertilizer treatment.The contents of dissolved,potassium permanganate oxidized carbon,non-labile organic carbon in deep soil were lower than those in surface soil.(3)The characteristic peak shapes of the infrared absorption spectra of the four monitoring sites in Wannian,Shanggao,Xingguo,Jinxian at 0～20 cm and 80～100 cm without fertilizer and conventional treatment are basically the same.The relative percentage of different types of carbon functional groups showed the same trend.These results indicated that fertilization method and depth had no effect on the chemical structure of soil organic carbon,and the similarity of chemical structure of exogenous carbon(organic fertilizer,rice roots,stubble)was the main reason for the similarity of chemical structure of organic carbon.(4)In the topsoil,the ratios of aliphatic C/aromatic C and alkyl C/alkoxy C ranged from 3.05～7.21 and 0.39～0.65,respectively,and the aromaticity ranged from 0.12～0.25.In the deep layer(80～100 cm),the ratios of aliphatic C/aromatic C,alkyl C/alkoxy C were1.98～8.03 and 0.20～1.29,respectively,and the aromaticity was between 0.11～0.34.Compared with the no-fertilizer treatment,long-term conventional fertilization increased the surface stability of Wannian and Xingguo points,and decreased the surface stability of Shanggao and Jinxian points;increased the deep stability of Shanggao and Xingguo points,and increased the stability of Wannian and Jinxian points.The deep stability of the Yin point has been reduced.(5)Under the condition of long-term conventional fertilization,the ratio of(Gal + Man)/(Ara + Xyl)in the deep layers of Wannian,Shanggao,Xingguo and Jinxian sites were all higher than those of surface layer,which increased by 41.94%,1.98%,32.98% and 7.32%,respectively.Under the condition of long-term conventional fertilization,the ratio of Glu N/Mur N in the deep layer of Wannian,Shanggao and Jinxian points was higher than that in the surface layer,increasing by 14.97%,19.59% and 32.84%,respectively;the ratio of Glu N/Mur N in the deep layer of Xingguo point is lower than that in the surface layer,decreasing by 9.88%.This shows that compared with the surface soil,the organic carbon of microbial origin in the deep soil of the four sites increased under long-term fertilization conditions;the relative contribution of fungal residues in the deep soil of Wannian,Shanggao and Jinxian sites was greater than that of bacteria,while the Xingguo site the relative contribution of bacterial residues in deep soil was greater than that of fungi.(6)The interpretation rate of soil properties to the total variance variation of soluble organic carbon content at Wannian,Shanggao and Jinxian points was 83.2%.Among them,p H,AN,AP and SOC could explain 0.9%(P < 0.05),70.1%(P < 0.01),6.8%(P < 0.01)and 5.0%(P < 0.01)of the variation of soluble organic carbon content,respectively.The interpretation rate of soil properties to the total variance variation of potassium permanganate oxidized carbon and non-labile organic carbon content at Wannian,Shanggao,Xingguo and Jinxian sites was 92.6%.p H,AK,AN,AP and SOC could explain1.1%(P < 0.01),1.1%(P < 0.01),0.9%(P < 0.01),0.7%(P < 0.01)and 88.4%(P < 0.01).Therefore,p H,AK,AN,AP and SOC are the main factors affecting the content of organic carbon in typical paddy soil under long-term fertilization in Jiangxi Province.