Influence of Long-term Fertilization on Content and Distribution of Organic Carbon in Particle-size Fractions of Red Soil and Fluvo-aquic Soil in China

【Objective】 The objective of this study was to clarify the effect of long-term fertilization on content and distribution of organic carbon in particle-size fractions in red soil and fluvo-aquic soil, and discuss fertility maintaining model for sustainable land use.【 Method】 The red soil and fluvo-aquic soil with different long-term fertilizations, collected from the seventeen years filed experiments, were separated into sand, coarse silt, fine silt, coarse clay and fine clay by physical way, and the content and distribution of organic carbon in these particle-size fractions were analyzed. 【Result】 Compared with treatment of CK, the treatment of M, NPKM and NPKS significantly increased the content of total organic carbon (TOC) and organic carbon in particle-size fractions in the two soils, however, application of chemical fertilizer was more favorable for increasing organic carbon in fine clay. Application of manure was the most effective practice for increase soil organic carbon. The POC in sand was the most sensitive fraction to the fertilization among the particle-size organic carbon fractions, as its increase extent of the content was the highest after fertilization and reached 1.7-3.8 times and 1.9-2.8 times in the red soil and fluvo-aquic soil, respectively. The distribution percentage of organic carbon in sand was significantly increased after fertilization by 37.7%-91.5% and 63.6% in the red soil and fluvo-aquic soil, respectively. However, the percentage in different-sized clay and silt was significantly different, but it was decreased as a whole, followed by corresponding increase the ratio of POC to MOC (WPOC/WMOC), which aroused improvement of soil organic carbon. 【Conclusion】 Loam red soil could retain more organic carbon than light fluvo-aquic soil and the application oforganic manure or straw is a better way to increase organic carbon in particle-size fractions of the two soils.