Assessing soil organic carbon stocks under different land uses in Uganda.

Abstract

Currently, there is a lot of debate on the total potential of agricultural soils to store additional carbon, the rate at which soils can accumulate carbon, the permanence of this sink, and how best to monitor changes in soil organic carbon stocks. The general lack of research in this area is currently preventing a more quantitative assessment of the carbon sequestration potential of soils across land uses, yet soil information is relevant for the transfer of soil technologies, estimation of amounts and distribution of carbon stocks, provision of data to support model simulations of soil carbon change, and provision of relevant information for the establishment of the national soil monitoring system. This study assessed soil organic carbon stocks and the determinants across land cover tyes (Cropland, Forestland, Grassland and Wetland). Soil organic carbon stocks were calculated using models suggested by IPCC (2006) and outlined in the REDD+ methodological module (2009). The determinants of soil organic carbon stocks were assessed through a regression analysis using a mixed-effect generalized linear regression model. Croplands contained, on average 17.95, 29.74, 34.84 and 37.01 Tc/ha for 0-15, 15-30, 30-45 and 45-60cm depths, respectively; forestlands had 127.78, 167.12, 148.47 and 124.49Tc/ha for 0-15, 15-30, 30-45 and 45-60cm respectively; grasslands had 55.30, 70.35, 81-83 and 73.17Tc/ha for 0-15, 15-30, 30-45 and 45-60cm respectively, while wetlands had 6.36, 10.785 14.59 and 15,47Tc/ha for the same respectice soil layers. SOC stocks were found to vary significantly across land uses. Regression analysis revealed that SOC stocks are significantly influenced by type of land use, bulk density of the soil, altitude, silt and clay contents of the soil. Within the same land use class such as cropland, different crop cominations store different carbon in the soil. Therefore, there is need to assess soil organic carbon stocks at landscape and plot level so as to identify appropriate plant, tree and crop species with abilities to enhance soil organic carbon storage and develop carbon sequestration finance programs that focus on livelihood and income improvement so that there is an incentive for farmers to invest in climate smart agriculture.