CHANGES IN SOIL CARBON AND TOTAL NITROGEN FOLLOWING REFORESTATION OF PREVIOUSLY CULTIVATED LAND IN THE HIGHLANDS OF ETHIOPIA

Abstract

Changes in soil C and total N stocks were investigated following reforestation of
previously cultivated soil in compariso n with soil subjected to continuous cultivation and soil under an
adjacent natural forests in south central highlands of Ethiopia. Two of the most widely planted tree
species in the highlands of Ethiopia, namely Eucalyptus saligna and Cupressus lusitanica, were considered
in the plantation treatments. Soil C and total N contents in the upper 0–10 and 10–20 cm soil layers were
significantly different in the order: Natural forest > C. lusitanica > E. saligna > Farmland. Differences in
soil C and total N contents among the sites for soil depths greater than 20 cm were negligibly small and
statistically not significant. Soil C and total N stocks in the upper 0.80 m mineral soil also varied
significantly in the same order as above. Estimated average annual soil C accruals were 156 and 37 g C
m-2 yr-1 for Cupressus lusitanica and Eucalyptus saligna, respectively. The results demonstrate that
reforestation of former arable soils in the dry Afromontane region of Ethiopia could yield significant
restoration of soil C and total N that are lost in the process of natural forest conversion into arable lands
and subsequent cultivation. However, the two plantation species differed considerably with respect to
the rate of soil C and total N accrual. This suggests that proper selection of tree species will considerably
affect the magnitude and rate of soil C sequestration