Factors controlling potentially mineralizable and recalcitrant soil organic carbon in humid Asia
2010
Kadono, A., Tokyo Metropolitan Univ., Hachioji (Japan) | Funakawa, S. | Kosaki, T.
To understand and estimate soil organic carbon (SOC) sequestration and depletion potentials in humid (monsoon) Asia, it is necessary that factors controlling the SOC pools with different turnover rates be determined. Eighty-nine surface soil samples were collected in Thailand, Indonesia and Japan from cropland and forest ecosystems. The SOC was fractionated to two pools: potentially mineralizable organic carbon (PMC) and recalcitrant organic carbon (ROC). The PMC for the soils was determined by fitting models to the cumulative curves of CO2 released during incubation of the fresh soils under constant temperature and moisture conditions. The ROC was determined by subtracting PMC from total carbon (TC). The soil and meteorological properties were divided into five factors using principal component analysis: 'light fraction (LF)', 'amorphous', 'clay', 'humid and warm' and 'carbon to nitrogen ratio (C:N)'. Using multiple regression analysis and a stepwise method, equations were determined that could be used to estimate PMC and ROC using the five identified factors as follows: PMC (mg C/kg) = 4044 + 2629 x (LF factor) + 1072 x (clay factor) + 751 x (humid and warm factor) (N = 81, R**2= 0.63**), ROC (g C/kg) = 45.3 + 24.5 x (LF factor) + 12.6 x (amorphous factor) + 8.8 x (clay factor) - 7.2 x (humid and warm factor) + 3.4 x (C:N factor) (N = 81, R**2 = 0.91**). PMC was well estimated by the LF and clay factors. This suggests that both the clay-associated organic matter as well as the LF are partially labile in nature. Major factors controlling ROC were LF organic matter, amorphous materials and clay content, suggesting the importance of parent materials in estimating the amount of recalcitrant organic matter in humid Asia.
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