Soil Organic Carbon Stock Tracking in Uganda
Estimation of the size and changes of soil organic carbon (SOC) stocks is of great importance for decision makers to adopt proper measures to protect soils and to develop strategies for mitigation of greenhouse gases. In this study, we assess the relationship between soil organic carbon stocks and different land management practices by farmers at different landscape positions across nine Agricultural Production Zones (APZs) of Uganda. This is done systematically by:
(1) conducting household surveys from three purposively selected sub counties, one each, from three selected districts in each of the nine APZs. For every selected sub-county, six households are randomly selected from each of the landscape positions (shoulder/ upper slope, mid slope, lower slope/ valley bottom) present in the area of interest and interviewed to collect plot level information e.g. the land management history. This is intended to establish the link between SOC levels of the sampled soils, the prevailing land management practices and landscape positions. A total of 18 households are interviewed per sub-county in each district, bringing the total number of households interviewed per APZ to 54 (18hh x 3 districts x 1 APZ) and the total sample size for this survey to 486 households (54hh x 9 APZs);
(2) after a brief interview with the household head, a one acre plot is purposively selected (should be representative of that particular landscape position) and about 15 soil cores obtained from a depth of 0-20 cm, mixed up thoroughly to make a homogenous sample (of about 100 g) which is then sent to the laboratory at the National Agricultural Research Laboratories (NARL) – Kawanda for analysis.
While sampling, great care is taken to avoid particular spots like old fence lines, old compost pits, and termite hills that can potentially bias the SOC results. In total about 54 homogenous core samples are obtained from every APZ. These sampling/ augering points have elevation and spatial information (Lat/Long) and therefore will be processed in GIS environment to produce the Soil Organic Carbon Stocks Map of Uganda. Since samples are taken from only a few representative selected sub counties in a district, statistical interpolation is employed to have an estimate of soil organic carbon stocks for places where no samples were picked. Therefore supplementary field surveys will be conducted to validate the soil organic carbon stock map and determine its accuracy.
Dr. Drake. N. Mubiru, Principal Scientist-NARO and SLM Project Coordinator;
Mr. Joram Bahati, Research Assistant-NARL-Kawanda and;
Mr. Joseph Tamale, Soil Fertility Scientist-Ngetta Zonal Agricultural Research and Development Institute (NgeZARDI).