Effect Of Long-term Fertilization And Soil Management Regimes On Soil Organic Carbon And Its Fraction On Loess Soil

Soil organic carbon (SOC) is the most important indicator of soil quality,since it profoundly influence in soil physical, chemical and biological properties. Increasing soil organic matter not only contributes to agricultural development, but also to the entire global ecosystem. However, soil total organic carbon (TOC) is not very sensitive to soil management practice changes because of the large background value in nearly all soils. We investigated the responses of four labile fractions of soil organic carbon, specifically, particulate organic carbon (POC), light fraction organic carbon (LFOC), microbial biomass carbon (MBC) and dissolved organic carbon (DOC), to management practices.20-year long-term field experiment on loess soil was employed, it comprises two systems: 1) The soil management system, include cropland abandonment (Abandonment), bare fallow without vegetation (Fallow) and 2) The nutrient management practices for wheat-maize cropping system were control (CK, no any nutrient input), N, NK, PK, NP, NPK, straw plus NPK (SNPK) and manure plus NPK (M1NPK and M2NPK).1. The results revealed that soil management had significant effects on SOC and its fractions. Abandonment was more conducive to increase soil organic carbon than Fallow and winter wheat-summer maize rotation, in sharp contrast, bare fallow without vegetation cover was not effective for soil organic carbon sequestration. Under cropping system, balanced fertilization could promote soil organic carbon content. Organic manure plus NPK significantly increased soil organic carbon content, organic manure play an important role of soil organic carbon sequestration.2. Different soil managements had significant effects on SOC and its fractions dynamics, Abandonment was conducive to the increased in SOC, POC and LFOC, and the levels of these three parameters were linearly increased as a function of time. Under cropping system, SOC, POC and LFOC showed growing trends on treatments those receiving both N and P(NP and NPK), while those treatments given no N (PK) or no P (N and NK) decreased the LFOC and DOC contents. Addition of organic materials integrated with NPK, and organic manure in particular, substantially enhanced the levels of all SOC fractions. LFOC and DOC exhibited quite different trends from that of SOC, while the POC had a consistent trend with SOC, could better reflected the trend of soil organic carbon changes induced by fertilization and management practices.3. Different soil management regimes significantly changed the distribution of water stable aggregates, Abandonment increased the proportion of water stable aggregates larger than 2mm , and SOC contents in all aggregate sizes. Under cropping system, fertilizer application had the tendency to increase the percentage of >2mm water stable aggregate. The fertilization, especially the organic materials plus inorganic fertilizers significantly increased SOC levels in aggregates of all sizes, the order of SOC contents in aggregates was M2NPK > M1NPK > SNPK > NPK > NP> PK > N > NK > CK. Long term inorganic fertilizer application or combining inorganic and organic fertilizers enhanced the allocation of SOC in macro aggregates ( (>0.25mm) and decreased the percentage of SOC in micro aggregate (<0.25mm).4. Stalk plus NPK (SNPK) and manure in addition of NPK (MNPK) significantly increased the levels of MBC and DOC in both rhizospheric and bulk soils. In wheat growth season, the highest MBC levels on all treatments were found to be at flowering stage at which the DOC level was the lowest among all growth periods. There were no significant changes in MBC and DOC contents under maize growth period. MBC and DOC contents were higher in rhizospheric than in bulk soils under wheat growth period. As with in the maize season, only MBC showed higher contents in rhizospheric soils other than in bulk soils, DOC showed an opposite trend to MBC.