The effects of land use systems on soil organic carbon
and total nitrogen are presented in Tables 1 and 2. Soil
organic carbon was significantly affected by the type
of land use systems. In all soil depth, except 30-60 cm,
organic carbon is lower in cultivated fields as
compared to other land uses. For instance, the analysis
of surface sample (0-5 cm) at Sinana Dinsho showed
that the highest SOC (12.95%) was recorded from
soils under virgin forest and the least SOC (2.75%)
was in cultivated soil. Similarly, the highest SOC
(7.58%) was recorded in soils under grassland
followed by fallow lands (4.09%) and the least in
cultivated soils (2.56%) at Gassera district in similar
depth. Most cultivated soils of Ethiopia are poor in
organic matter contents due to low amount of organic
materials applied to the soil and complete removal of
the biomass from the field (Yihenew, 2002), and due
to severe deforestation, steep relief condition,
intensive cultivation and excessive erosion hazards
(Eylachew, 1999). In agreement with this all
agricultural fields in the study areas had low organic
carbon content according to the classification
presented in Landon (1984). Barrow (1991) states that
an organic matter content of less than two per cent for
tropical soils is an indication of soil degradation
involving a highly raised risk of soil erosion.