Assessment of soil organic matter under four land use systems in Bale highlands, Southeast Ethiopia: A. Soil organic matter contents in four land use systems: forestland, grassland, fallow land and cultivated land.

2 Abstract: A study to assess soil organic matter (SOM) stock and its distribution under four land use systems in major soils of Bale highlands were conducted in 2005. in which major soil parameters of SOM storage as affected by four land use systems in 0-5, 5-15, 15-30 and 30-60 cm soil depths were evaluated. The result indicated distribution and abundance of soil organic carbon (SOC) in all land use systems was affected differently. The commonality trends were a consistent decrease in SOC content with increasing soil depths in all land use systems across locations. Highest SOC content (12.95%)(0-5 cm) and lowest 2.86% (30-60 cm) were in the forestland use of Sinana-Dinsho soils. Whilst the lowest SOC and TN stocks were found in cultivated and fallow lands of the three Districts in a range of degradation. The critical element, total nitrogen (TN) was affected by land use systems. The highest TN (0.8%) (0-5 cm) and the lowest (0.2%) (30-60 cm) was in the forestland use of Sinana-Dinsho districts. The C:N ratio was lower in the cultivated soil 10:1- 15:1 indicating more SOM mineralization. However, C:N ratio (20.1:1 to 27.4:1) (0-5 cm) in virgin forest soil indicated TN in neither mineralization nor immobilization process. In all soils under investigation, pH (5.8-7.2) was not in low level to restrict root growth for crop production. Need to restore fertility of long cultivated land, land use policy for proper land use systems to sustain productivity of land, follow-up of similar work in lowland soils; to restore natural soil fertility, sequester SOC and TN, increase soil biological activity and provide precise information which supports to fill the potential gap in crop production were recommended.