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 comparison 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.

Keywords: continuous farming, Cupressus lusitanica, Eucalyptus saligna, soil carbon sequestration, soil carbon loss

SINET: Ethiopian Journal of Science Vol. 28(2) 2005: 99-108