Comparison of soil attributes under Cupressus lusitanica and Eucalyptus saligna established on abandoned farmlands with continuously cropped farmlands and natural forest in Ethiopia

Soil attributes under two fast growing exotic plantations (Cupressus lusitanica and Eucalyptus saligna) established on abandoned farmlands were compared with soils of mechanized farming (MF), traditional farming (TF) and adjacent natural forest in Ethiopia. The plantations were established on an abandoned part of the MF site. All soils in the study were Humic Haplustands. Fifteen years after plantation establishment, the surface soil (0–10 cm) under C. lusitanica had lower bulk density, higher soil C, total N, cation exchange capacity (CEC), base saturation (BS), available K, exchangeable K, Ca, and Mg than the soils of MF and TF. On the contrary, the same soil layer under E. saligna had lower soil C, total N, BS, CEC, available P, available K, and exchangeable Ca than the soils of TF and MF. Except for some soil properties under C. lusitanica that showed consistently high concentrations, most soil properties in the sub-soil layers (10–20 and 20–40 cm) did not show clear differences between the sites as in the surface 0–10 cm soil layer. Comparison of the two farming situations showed higher soil compaction and poorer soil status under MF than TF. Computed deterioration index (DI) revealed a high positive index for the soil under C. lusitanica (DI=+337) suggesting a cumulative positive effect of the species on soil properties. Soil properties deteriorated under E. saligna (DI=-198) even compared to the soils subject to MF and TF (DI=-185 and -77, respectively). We concluded that forest plantations can be used to facilitate soil restoration on degraded farmlands, but that the degree, rate and direction of changes in soil attributes are species dependent. We suggest that long-term effects on soil properties should be considered as one of the criteria when selecting species for afforestation or reforestation of degraded farmlands.