Effects Of Long-Term Fertilization On Soil Properties And Organic Carbon Pools And Chemical Structure Of An Ultisol

Ultisol, the most widely distributed soil in southern China, covering1.13million square kilometers, accounting for11%of the total land, which has low organic matter and low soil fertility, and intense compaction. Thus, the scientific issues related to how to increase soil organic carbon (SOC), then improve the soil structure, finally enhance the soil productivity is urgent to be solved. It is well known that the long-term fertilization could alter the soil properties, as the result of the changes of soil organic matter structure and organic carbon pools. So the combination experiments of indoor and field including the long-term different fertilizer on the soil properties, corn yields, soil organic carbon pools distribution and turnover rates, and the structure of soil organic matter were investigated from a long-term fertilization experiment since1986in an Ultisol of subtropical China (Jinxian County, Jiangxi Province). The main results are showed as follows:1. The long-term fertilization treatments significantly changed the soil properties. In all fertilization treatments, the soil chemical properties including the contents of SOC, labile organic carbon (LOC), pH, Cation exchange Capacity (CEC), total nitrogen (TN), and total phosphorus (TP) were highest after the application of organic fertilizer (NPKOM, OM). Furthermore the>0.25mm water stable aggregate content, soil aggregate stability, and also the corn yields were greatest in these two treatments. Long-term fertilization significantly affected soil microbial biomass, especially the organic fertilizer which significantly increased soil microbial biomass carbon (SMBC), microbial biomass nitrogen (SMBN) and microbial quotient (qMB). Compared with control treatment (CK) and the applications of nitrogen without phosphorus (N, NK), the application of organic manure, especially the combined application of inorganic and organic fertilizer, not only effectively reduced soil acidification, but also significantly improved the qMB and the structure of soil microbial community, as the consequence benefited to the maintenance of soil fertility. 2. Through SOC physical fractionation and chemical analysis methods, the results showed that:s+c_M and s+c_mM associated C accounted for31%～53%and28%～38%of SOC, followed by fPOM (8%～15%) and iPOM_mM (7%～21%), and then by cPOM (5%～12%). Organic fertilizer application (NPKOM, OM) significantly increased POM associated C pools (cPOM、fPOM and iPOM_mM), but had no significant effect on mineral associated C pools (s+c_M and s+c_mM). As a result, the turnover rates of SOC were the fastest in the two treatments.3. The long-term fertilization treatments changed the chemical structure of soil organic matter. Compared with CK, chemical fertilizer treatments reduced the alkyl C (0.3%～21.1%) and0-alkyl C (0.4%～7.8%), respectively, but increased the aromatic C (3.4%～21.4%) and carboxyl C (1.1%～24.5%), respectively, expect for the application of K. Moreover, the application of organic fertilizer (NPKOM, OM) enhanced the carboxyl C (17.0%～20.2%). While NPKOM and OM only lightly increased alkyl C and O-alkyl C contents, and aromatic C, respectively, within the low increasing rate. Compared with CK, the organic fertilizer improved the ratios of alkyl C/O-alkyl C and aliphatic C/aromatic C, and also aromatic C content resulted into the aliphatic improvement of soil organic matter and more complex and aliphatic structure of organic matter molecular, which was favorable for enhancing the stability of SOC and soil aggregate.