Abstract:
Among several agroforestry practices in the east Hararghe of Ethiopia, Parkland agroforestry practices are common. However, the beneficial effect of tree species on soil properties is very scarce to be used for improved agricultural productivity in the eastern part of the country including study area. Therefore, the study was conducted with the objectives of investigating the impact of parkland trees on the soil physical and chemical properties within and outside the trees canopy; the vertical and horizontal soil fertility gradients as influenced by the tree species and the effects of trees on yields of sorghum (biocolar) in Fedis District, Oromia, Ethiopia. Accordingly, six isolated and nearly similar F. albida and C. africana trees of each species growing on similar site conditions were selected and the canopy coverage of each tree was divided into four radial transects. Radial distance-based soil sampling (under the canopy, edge to canopy, and far from canopy) was used and composite soil samples from three horizontal distances with two soil depths were collected for analysis of soil physical and chemical properties. Three plots from the tree trunk were also established for assessing the sorghum yields. The result revealed that lower soil bulk density was observed under tree canopy than open field(p<0.05) While soil moisture content was significantly (p<0.05) higher under canopy of trees than open fields. Soil chemical properties (EC, SOC, OM, Soil CS, total N, available P, exch. Na, exch. K, exch. Ca , exch. Mg and CEC) were significantly (p<0.05) higher under the tree canopies than open field and in surface than subsurface soil. The study also showed that the grain yield of sorghum (biocolar) were significantly (P<0.05) higher under canopy of both trees species as compared to the open field. An increased by 84.3% and 71.5% for OC, 84.2% and 70.8% for OM, 66% and 59% for SOC Stocks, 82% and 84% for TN, 96% and 79% for AvP, 15.6% and 34.2% for CEC, 30% and 10% for EC, 82% and 27.2% for Na,41% and 30.4% for K,33.8% and 28.2% for Ca and 58% and 87% for Mg and 13.22% and 13.15% for MC and decline by 10.3 and 8.5%% in BD and by 43%and 41% for Sorghum yield were detected under the canopies of F. albida and C. africana tree species respectively. Retaining these tree species and in particular F. albida on crop field in the study area is of paramount importance for soil fertility enhancement so as to improve food security of small farming households.
