Tropentag, September 19 - 21, 2012 in Göttingen "Resilience of agricultural systems against crises"

Understanding Soil Organic Carbon Dynamics at the Landscape Scale: Hotspot Mapping

¹International Center for Tropical Agriculture (CIAT), Kenya
²World Agroforestry Centre (ICRAF), Kenya
³International Center for Tropical Agriculture (CIAT), Trop. Soil Biology and Fertility (TSBF), Malawi
⁴International Center for Tropical Agriculture (CIAT), Soils Program, Mali

Abstract

Soil organic carbon is an important indicator of soil health as it integrates inherent soil properties as well as aboveground landscape dynamics, including land-use change. Establishing regional soil organic thresholds using systematic and spatially explicit baseline data can guide restoration activities and land-use planning. The Land Degradation Surveillance Framework offers a methodology to assess soil organic carbon values and stocks across the landscape, while accounting for the variability at three different spatial scales. Seven sentinel sites were sampled in Tanzania in 2010. Each site has 160 plots, where topsoil (0-20 cm) and subsoil (20-50 cm) as well as cumulative mass samples were collected, current and historic land use was recorded, and vegetation measurements were made. A total of 1,993 plots were included in the current study. Average topsoil organic carbon was 10.9 g C kg^-1 (n=1058) and average subsoil organic carbon was 8.3 g C kg^-1(n=935) for the seven sites. Organic carbon concentrations measured in the lab were related to satellite image reflectance data using multilevel and ensemble models, and predictive maps were generated. These maps were also used to assess spatial patterns and landscape features that influence soil organic carbon concentrations and to identify low-carbon hotspot areas. These results can also be useful for establishing regional soil organic carbon reference values, for example according to climatic zones and native vegetation types. The systematic sampling employed in this study allows for robust comparisons of soil organic carbon values and soil mass within and between land uses and at different spatial scales.

Keywords: Hotspot mapping, landscape assessment, soil organic carbon

Contact Address: Leigh Winowiecki, International Center for Tropical Agriculture (CIAT), ICIPE Duduville Complex, Box 823-00621, Nairobi, Kenya, e-mail: l.a.winowieckicgiar.org