Abstract:
Land degradation, which includes degradation of vegetation cover, soil degradation and nutrient
depletion, is a major ecological problem generally in Ethiopia and particularly in the study area.
As a response of the ever expanding land degradation, rehabilitation of degraded lands through
closed areas has been practiced in the study area. Despite this concern, there are relatively few
studies in the study area, which would provide a measure of usefulness of closed areas as one
strategy to help prevent decline of soil degradation and thereby increase agricultural
productivity. A field study was conducted in the Busuqi and Gubesay Peasant Association of
Adaa'a wereda, Eastern Shewa zone, Oromia Region of Ethiopia to assess the effects of area
closure on soil nutrients and on gully and sheet erosion. To this end enclosure sites are compared
with other land use types (free grazing land) in similar landscape positions for soil fertility
buildup, sheet erosion, and gully erosion. Soil samples were collected accross two parallel
transects from the three land use types. Status of degradation of different land use types; young
Kelala enclosure, free grazing land and old Biyo enclosure, was assessed using SOM, CEC, TN,
PH, AP, AK, BD, gully parameters and sheet erosion rate . Degradation Indices were computed
for young Kelala enclosure and free grazing land through comparison with the old Biyo
enclosure. The rate of soil loss through sheet in the study area was determined using erosion
Pins. Five and twenty one year closed areas had significantly (p < 0.05) higher levels for SOM,
CEC, TN and AK compared to free grazing lands. The soil physical properties such as bulk
density, showed notable variations, particularly due to different land use system. The highest bulk
was recorded in the free grazing land, whereas the lowest was in old Biyo enclosure. AK was the
most deteriorated soil parameter with values of 35.25 (%) and 47.31(%) for young Kelala
enclosure and free grazing land respectively. SOM was the next deteriorated soil parameter with
values of 44.05 for free grazing land. TN was the next deteriorated soil parameter with values
of 26.92 (%). Among the two land use types selected to be studied, free grazing land was the
most degraded one with a degradation index of -150.95% with respect to the old Biyo enclosure.
The calculated soil loss using Pin method indicated that there is significant difference (p < 0.05)
between Kelala Dalacha closed areas and adjoining free grazing land. Gully density of 14m/ha
was recorded in the enclosed side and 28m/ha in the free grazing side, which implies that the
sampled farm land bellow enclosure area was severely degraded and sampled farm land bellow
free grazing land was very severely degraded. The soil loss by sheet erosion was 0.37 mm /yr and
1.68 mm /yr for young Kelala enclosure and free grazing land respectively. The overall output
from the research showed that chemical and physical soil properties in enclosure areas with
restoring vegetation are improving that enclosures act as important sinks of water and reduce
soil erosion and as such contribute to soil and water conservation. If appropriate interventions
are not carried out in the free grazing land for the future, the soil nutrient deplition extent and
soil erosion rate would escalate and reversing the process would become difficult
Keywords: land use, closed areas, free grazing land, soil nutrients, erosion, Pin, gully density