Long-Term Impacts of Cultivation and Residue Burning Practices on Soil Carbon and Nitrogen Contents in Cambisols of Southwestern Ethiopia

Soil organic carbon (OC) and total nitrogen (N) are important indices for evaluating land management system, so that assessing the management effects on soil OC and total N dynamics is essential for addressing sustainable land productivity and environmental quality issues. This study was carried out to determine the impact of long-term agricultural practices on the distribution and contents of OC and total N in Cambisols of Abobo, southwestern Ethiopia. Three adjacent fields: Cultivated field with continuous residue burning (CB), Grassland with annual burning (GB) and the Virgin land with native vegetation (VL) were used in this study. The soil in VL was used as a reference to assess extent of changes in soil OC and total N contents. Composite soil samples were collected from four soil depths (0-15, 15-30, 30-45 and 45-60 cm) of each land units, in the triplicate sites. A one-way ANOVA and correlation coefficient analysis were used to test the mean differences of the soil OC and total N contents in each soil depth, and to determine their degree of association with other soil variables. The result revealed that the existing management practices significantly affected soil OC and total N contents in all the studied soil depths. The depletion of soil OC and total N from CB and GB fields were up to 83 and 66%, respectively, as compared to those in the VL. Changes in soil OC and total N were more pronounced in the top 30 cm depth of soil, although significant reduction observed in the 30- to 60 cm depth. The contents of deeper soil layers (45-60 cm) in burned and burned/cultivated sites were comparable, implying that immediate fire/tillage impacts were restricted to the near surface soil depth. The overall results suggest that the existing land management is not sustainable; hence, proper residue management is imperative in order to sustain the soil quality and maintain long-term productivity of the farmland.