Abstract
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 [0–30 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—forest, cassava, and rice paddy—in Northeast Thailand. Sequestration of SOC in topsoils under all land uses was higher, as indicated by SOC stocks (59.0–82.0 Mg ha−1) than subsoils (30–100 cm) (27.0–33.0 Mg ha−1). The soil profile (0–100 cm) of the forest had higher stocks of SOC and humic acid (115.0 and 6.8 Mg ha−1, respectively) than those of cultivated land uses [paddy (100.0 and 4.8 Mg ha−1, respectively) and cassava (87.0 and 2.3 Mg ha−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 (3.2–3.6). Subsoil C was higher quality, as indicated by the lower E4:E6 ratio of humic acids than topsoils in all land uses.
Highlights
Soil organic carbon (SOC) is the largest reservoir of C in active exchange with atmospheric carbon dioxide (CO2 ), changes in the SOC pool exert substantial impacts on global climate [1].Land–use changes from forest to cultivated lands, in the tropics, are responsible for 12–20%of greenhouse gas emissions induced by humans [2,3]
Carbon stocks in topsoils (0–30 cm depth) of the three different land uses ranged from 59.0 to 82.0 Mg ha−1 (Figure 3a) and accounted for 68–73% of total SOC stock in the whole soil profile. These carbon sequestration values were of the same magnitude as those found in the literature; for example, soil under pure Cedrus deodara forest had SOC stocks that amounted to 49.0 Mg ha−1 higher than those of agricultural land (29.0 Mg ha−1 ) throughout a 0–30 cm soil depth [50]
The largest share of SOC was found in the topsoil (0–30 cm), we found that the subsoil (30–100 cm) accounted for an average of 30% of the total amount of C in the whole profiles in all land uses in our study
Summary
Soil organic carbon (SOC) is the largest reservoir of C in active exchange with atmospheric carbon dioxide (CO2 ), changes in the SOC pool exert substantial impacts on global climate [1].Land–use changes from forest to cultivated lands, in the tropics, are responsible for 12–20%of greenhouse gas emissions induced by humans [2,3]. Soil organic carbon (SOC) is the largest reservoir of C in active exchange with atmospheric carbon dioxide (CO2 ), changes in the SOC pool exert substantial impacts on global climate [1]. Land–use changes from forest to cultivated lands, in the tropics, are responsible for 12–20%. Of greenhouse gas emissions induced by humans [2,3]. This land–use change is the second largest source of greenhouse gas emissions [2], CO2 emissions [3]. Conversion from forest to agricultural land involves burning of vegetation and surface litter and soil disturbance through plowing, which accelerates decomposition of both soil protected and non–protected SOC, which leads to changes in microbial communities and activities contributing to C loss. The C loss is in terms of CO2 emission and involves rapid loss of C by leaching to subsoils [5,6]
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