Chaplot V., Podwojewski P., Phachomphon K., Valentin C.
Centre IRD d'île de France, 32, avenue Henri Varagnat, 93143 Bondy Cedex, France; School of Bioresources Eng. and Environ. Hydrology, Rabie Sanders Bldg., Univ. of Kwazulu-Natal, Scootsville, 3209, South Africa; Soil Survey and Land Classification Center, National Agric. and Forestry Research Institute, Vientiane, Laos
Chaplot, V., Centre IRD d'île de France, 32, avenue Henri Varagnat, 93143 Bondy Cedex, France, School of Bioresources Eng. and Environ. Hydrology, Rabie Sanders Bldg., Univ. of Kwazulu-Natal, Scootsville, 3209, South Africa; Podwojewski, P., School of Bioresources Eng. and Environ. Hydrology, Rabie Sanders Bldg., Univ. of Kwazulu-Natal, Scootsville, 3209, South Africa; Phachomphon, K., Soil Survey and Land Classification Center, National Agric. and Forestry Research Institute, Vientiane, Laos; Valentin, C., Centre IRD d'île de France, 32, avenue Henri Varagnat, 93143 Bondy Cedex, France
The main objectives of this study were to evaluate soil organic C (SOC) variability in a representative hillslope of Laos and to quantify the impact of some environmental factors. We collected 2348 soil samples from 581 georeferenced soil pits within a hillslope of northern Laos under traditional shifting cultivation at 0- to 0.05-m depth and then every 0.1 m to 0.35-m depth. The SOC stocks at 0- to 0.05-m depth varied between 0.4 kg C m-2 (standard error of ±0.046 kg C m-2) and 1.9 (±0.22) kg C m-2 and stocks in the 0- to 0.35-m depth were between 2.6 (±0.29) and 11.4 (±1.31) kg C m-2. About 85% of SOC spatial variability occurred at a distance less than 20 m. As expected, SOC content and stocks at 0-to 0.05-m depth were significantly greater with higher soil clay content and shorter durations of cultivation (P < 0.001). But at 0- to 0.35-m depth, the significance of clay content was only P = 0.04 and stocks surprisingly increased with increasing slope gradient (P < 0.001). Thus, it seems that sloping lands under shifting cultivation act as a conveyor that stores atmospheric inorganic C in soils during the regeneration of natural fallows and ultimately transfers it by water erosion to the steepest areas of hillslopes, where it accumulates, probably due to greater infiltration by water. These results on SOC spatial variations under steep slope conditions of the tropics give a better picture of SOC dynamics that may allow development of optimal strategies of land management to foster main soil functions and offset the current rise in atmospheric CO2. © Soil Science Society of America.
Atmospheric CO; Clay content; Current rise; Environmental factors; Hillslope; Hillslopes; Land managements; Optimal strategies; Slope gradients; Sloping land; Soil clay content; Soil erosion; Soil function; Soil organic C; Soil organic carbon; Soil pits; Soil sample; Spatial variability; Spatial variations; Standard errors; Steep slope; Water erosion; Clay minerals; Erosion; Fire hazards; Forestry; Land use; Organic carbon; Programmable logic controllers; Strategic planning; Soils; carbon dioxide; clay soil; environmental factor; infiltration; land management; shifting cultivation; slope dynamics; soil carbon; soil erosion; soil organic matter; spatial variation; water erosion; Asia; Eurasia; Laos; Southeast Asia