Land–Use Changes Influencing C Sequestration and Quality in Topsoil and Subsoil
2019
Benjapon Kunlanit | Somchai Butnan | Patma Vityakon
Soil capacity as a major carbon (C) sink is influenced by land use. Estimates of soil organic carbon (SOC) sequestration have mostly focused on topsoils [0&ndash:30 cm official Intergovernmental Panel on Climate Change (IPCC) soil depth]. We investigated SOC stocks and their quality as influenced by land-use changes. Soil samples were collected from five soil depths down to 100 cm of three adjacent fields each representing a different land use&mdash:forest, cassava, and rice paddy&mdash:in Northeast Thailand. Sequestration of SOC in topsoils under all land uses was higher, as indicated by SOC stocks (59.0&ndash:82.0 Mg ha&minus:1) than subsoils (30&ndash:100 cm) (27.0&ndash:33.0 Mg ha&minus:1). The soil profile (0&ndash:100 cm) of the forest had higher stocks of SOC and humic acid (115.0 and 6.8 Mg ha&minus:1, respectively) than those of cultivated land uses [paddy (100.0 and 4.8 Mg ha&minus:1, respectively) and cassava (87.0 and 2.3 Mg ha&minus:1, respectively)], which accounted for an average 30% increase in SOC sequestration over those with only topsoil. Topsoils of the forest had higher humic acid content but narrower E4:E6 ratio [the ratio of absorbances at 465 nm (E4) and at 665 nm (E6)] of humic acids (2.8), indicating a higher degree of humification and stabilization than the cultivated soils (3.2&ndash:3.6). Subsoil C was higher quality, as indicated by the lower E4:E6 ratio of humic acids than topsoils in all land uses.
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