Physico-chemical properties of soil under the canopies of Faidherbia albida (Delile) A. Chev and Acacia tortilis (Forssk.) Hayen in park land agroforestry system in Central Rift Valley, Ethiopia

This study was conducted to evaluate the effect of Faidherbia albida and Acacia tortilis on soil physico-chemical properties at Langano and Tuka in farm fields of Bora District where both trees are traditionally retained on the farm. At each site, four F. albida and four A. tortilis trees were purposively selected and soil sample collected from four directions at three distances (1.35, 3.35 and 26.35 m) from tree trunk and composite soil samples was taken for both physico-chemical analyses. Collected data was analyzed by two way ANOVA and mean separation with LSD (%). Mean moisture levels of all sites, 1.35 (14.32%) were significantly (p < 0.05) greater than that of openland (10.79%) at 26.35 m from tree trunk. Bulk density was also significantly affected by tree canopies (p<0.05). It increased from 1.20 g/cm3 under canopy to 1.29 g/cm3 in the openland. At both sites, pH was significantly lower (p < 0.05) under the canopy than out of the canopy (it was reduced from 6.05 under canopy to 7.00 at open land). Soil organic matter, total nitrogen available phosphorus, exchangeable calcium, exchangeable magnesium and cation exchange capacity were significantly higher (p < 0.05) under the canopy of trees as compared to openland. Apart from these, the recorded values of exchangeable sodium, potassium and electrical conductivity revealed statistically non-significant difference among the treatments. The research finding showed that trees have positive relation with availability of soil nutrient and to enhance these trees in the farm, farmers knowledge improvement and further research regarding tree age class should be conducted.   Key words: Parkland agroforestry, canopy position, soil physicochemical properties.