Abstract
Typical red soil samples were collected from 17 years long-term fertilization experiments in Qiyang county of southern China. Physical fractions of the red soil include free particulate organic carbon (fPOC), intra-microaggregate particulate organic carbon (iPOC) and mineral associated organic carbon (MOC), were measured and the effects of fertilization on changes of soil organic carbon (SOC) stocks were analyzed. The results indicated that application of manure and manure-mixed-chemical fertilizer (M, NPKM, 1.5NPKM) significantly enhanced SOC and changed its physical fraction distribution. The highest sequestration rate in fPOC (290.6∼408.3 kg·ha−1·yr−1), iPOC (162.0∼179.2 kg·ha−1·yr−1) and MOC (322.9∼514.5 kg·ha−1·yr−1) were observed in these treatments. However, the content of iPOC and MOC didn’t increase in unbalanced chemical fertilizer application treatments (NP, N) in red soil, and they maintained lower SOC sequestration rate. The percentage of SOC sequestration distribution in different physical fractions under balanced fertilization treatments (NPK) followed the order: MOC (45.2%∼62.7%) > fPOC (21.9%∼35.2%) < iPOC (15.1%∼20.0%). The highest percentage of MOC implied that SOC associated silt and clay were the primary mechanism of SOC sequestration in red soil.
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