Effects Of Different Fertilization Practices On Structure Of Aggregates And Stability Of Organic Carbon In Paddy Soil

The soil carbon pool is the biggest one in the earth surface system. Increasing SOC levels play a critical role in agricultural sustainability and, maybe more important, in mitigating greenhouse effects and global climate changes. Aggregate is considered as a substituted index of the stability of soil structure, and the mechanisms of SOC stabilization are associated with capacity of SOC sequestration. So the studies in this field will help the governments make efficient policies to increase SOC and reduce greenhouse gas emission. And the paddy soil is very important soil carbon pools of China, which is an especial artifical wetland soil under long-term paddy management.The studied soil sampled from long-term chemical/organic matter fertilizer field experiment maintained for 22 years, located in Jinxian Country, institute of red soil of Jiangxi Province. Treatments were: (1)CK, (2)N, (3)P, (4)K, (5)NP, (6)NK, (7)NPK, (8)2NPK, (9)NPK+0M. This paper aimed to study: l)the distribution pattern and stability of aggregates, and the content of organic carbon and nitrogen in different size aggregates under different fertilization practices; 2)the content of different soil organic carbon fraction, and the labile and recalcitrant indices for organic carbon under different fertilization practices; 3) the content of soil potential mineralized carbon under different fertilization practices, and the relation between soil potential mineralized carbon and organic carbon fraction in physical and chemic method. The results were expected to improve the understanding of the effects of different fertilization practices on the structure of aggregate and stability of SOC, which is helpful in optimizing paddy fertilization practices to increase carbon sequestration.Soil samples was separated four level by modified humid method: >2mm,2-0.25mm,0.25-0.053 mm <0.053mm. Among of those, 2-0.25mm occupied the most percentage with 39.59%-54.76%. Compared with CK, the treatments of P, K, NK and NPK+OM prominently increased the content of macroaggregates and the stability of aggregates; The content of soil organic carbon and nitrogen increased under long-term fertilizer practices, And the combined treatment of NPK+OM also increased the content of soil organic carbon and nitrogen in bulk soil and in different size aggregates; Organic carbon and nitrogen were mainly sequestrated in 2-0.25mm macroaggregate; C/N ratio of aggregates decreased with decrease of the aggregates size.SOC was divided into two basic fractions: labile(hydrolyzed) organic carbon and Non-hydrolyzable residue(NHC) by HCl and H₂SO₄ acid hydrolysis. In the H2SO4 method, the content of labile carbon under fertilization practices obviously decreased in the sequence of labile fraction I >labile fraction II. Compared with CK, the content of labile fraction I,labile fraction II and total labile carbon all increased under long-term fertilizer practices except K treatment, which the effect of N treatment was the most prominent. N treatment prominently increased the labile index for organic carbon(LIc), but K treatment prominently reduced it. NPK+OM prominently increased the content of labile organic carbon and LI_C. Compared with CK, the content of NHC increased except N treatment, which the effect of K and NPK+OM treatments were the most prominent. K treatment increased the recalcitrant index for organic carbon(RIc), and N and NPK+OM treatments reduced RI_C. It had positive liner relation between the content of different organic carbon fractions and TOC.Soil potential mineralized carbon and mineralization rate constant were obtained by ecological model based on mensurating the content of CO₂ emission through short-term lab incubation. The carbon mineralization rate increased prominently under NPK+OM in short-term incubation within 1-4 days, then declined gradually. Compared NPK+OM with CK, the content of soil potential mineralized carbon prominently increased by 243.43 mg kg^-1, and it also appear to be increased tendency under long-term fertilizer, which didn't reach significant difference level, and the effect of mixed fertilizer was higher than singal fertilizer. The soil potential mineralizable carbon had positive relation with the content of organic carbon combined with aggregates(>0.053mm) and labile organic carbon through hydrolyzation by H₂SO₄ and HCl.