Soil organic carbon and stable carbon locations in different textural paddy soils

Abstract

The objective of this study was to determine location of stable organic carbon identified by using appropriate indicator conducting with various soil-aggregate sizes of two textural paddy soils, loam (Ratchaburi series, Rb) and sandy loam (Ubon series, Ub ). Soil aggregate sizes were separated into: 4-2 mm (LMa), 2-1 mm (MMa), 1-0.25 mm (SMa), 0.25-0.053 mm (Mi) and <0.053 mm (FMi). Soil organic carbon (SOC), labile organic carbon (LOC) and non LOC:SOC ratio were determined and calculated. It was found that SOC content in loam and sandy loam were 1.073-1.557 percent and 0.377-0.823 percent, respectively; LOC content in loam and sandy loam were 0.721-0.885 mg/kg and 0.603-0.806 mg/kg, respectively; while non LOC:SOC ratio in loam and sandy loam were 0.909-0.954 and 0.811-0.925 respectively. In respect of soil aggregate sizes of both textural soils, SOC content in FMi was highest, 1.188 percent; while that in LMa was lowest, 0.92 percent. LOC content in LMa was highest, 0.798 mg/kg; while that in Mi was lowest, 0.641 mg/kg. And non LOC:SOC ratio in Mi was highest, 0.935; while that in LMa was lowest, 0.875. The results from both textural soils led to a conclusion that aggregates of Mi has stability more than that of LMa by mean of the proposed mechanisms: clay–P–non LOC, clay–P–SOC, clay–P–LOC and clay–P–clay. The present research showed that non LOC:SOC ratio is an appropriate indicator, which is essential to explain soil-organic-carbon stability in soil aggregates. And it also revealed that non LOC contains with a large quantity as a major component of SOC more than LOC in each soil aggregate size.