Effects of data uncertainties on estimated soil organic carbon in the Sudan

Estimating the rate of soil carbon sequestration in degraded semiarid agroecosystems is of great interest due to the beneficial effects on soil properties, soil fertility, and the potential atmospheric CO2 mitigation. One of several applied methodologies, biogeochemical modeling, offers possibilities to distribute estimates of soil organic carbon (SOC) over regions, estimate the effects of changes in climate and ecosystem management on SOC, and quantify changes of soil properties over time or space. In this study, the sensitivity of the Century model was assessed in regards to uncertainties for soil texture, natural fire return periods, grazing intensities, and climate. The study area was situated in central Sudan and dominated by subsistence agroecosystems. Uncertainties in the modeling of historical SOC levels, prior to known human interactions, can be reflected in the estimation of the current or future SOC levels, as some soil processes take many years to occur. The relationship between these differences in historical and current SOC levels was calculated. Soil texture, derived from a number of different sources, had the greatest impact on modeled SOC. Overall, data uncertainties for the five parameters tested resulted in SOC variations of up to 160 g C/m(2) (1.6 t C/ha) for the estimation of the current level (year 2002), which corresponds to a difference of approximately 80% of the average current level.