Evaluation of soil physico-chemical properties as affected by canopies of scattered agroforestry trees on croplands

Agroforestry tree species play an important role in improving soil fertility. Though studies have confirmed that different species show different potentials to improve soil fertility, it is difficult to compare them as the studies were conducted in different areas. The potential for different tree species to improve soil fertility on croplands in northern Ethiopia is not known. The objectives of this paper are to determine the effects of presence or absence of agroforestry tree species on soil physico-chemical properties and the effect of distance from the tree trunk on the same soil physico-chemical properties. Sixty composite and undisturbed soil samples from beneath canopies and outside canopies and 90 composite and undisturbed soil samples from three different distances from tree trunks were collected. The results revealed that soil bulk density, soil moisture, soil organic carbon (SOC), total nitrogen (TN), available phosphorus (Av.P), exchangeable potassium (Exch.K) and soil organic carbon stock (SOCS) were significantly (p < 0.05) different between soils beneath canopies and outside canopies as well as at different distances from the tree trunk. Soils around these agroforestry tree species have increased SOC, TN, Av.P, Exch.K and SOCS by 11.9 to 91.5%, 22.2 to 125.0%, 31 to 71%, 32 to 151.6% and 15.2 to 90.9%, respectively, compared to soils outside tree canopies. Faidherbia albida (Delile) A.Chev. has the highest potential for soil fertility compared to Balanites aegyptiaca (L.) Delile, Cordia africana Lam., Ziziphus spina-christi (L.) Desf., Acacia sieberiana DC and Croton macrostachyus Hochst. ex Delile. This study could provide useful information for soil fertility management and farmers’ decision-making when selecting tree species. The findings of this study imply that scattered trees on croplands significantly improve soil fertility and reduce the need for external fertiliser inputs.