The effect of Balanites aegyptiaca, Acacia tortilis and Acacia seyal on soil fertility and microclimate was studied in the central rift valley of Ethiopia. Sampling was done in randomized complete blocks at 1/3 radius, 2/3 radius and at crown edge radius from the tree base and control was maintained at an open area. All soil and microclimatic parameters observed under the canopy distances were significantly different from the open control (P<0.05) except soil texture. Soil bulk density increased from the trees base to open field. Available Nitrogen under crown of A. tortilis in all crown radii was much higher than that of B. aegyptiaca and A. seyal; available Potassium was significantly higher under B. aegyptiaca and A. tortilis at their 1/3 and 2/3 crown radii. B. aegyptiaca at 1/3 crown radius had significantly higher level of available Phosphorus. Cation exchange capacity (CEC) was significantly higher under the 1/3 and 2/3 crown radii of all the involved trees. Soil moisture decreased whereas relative illumination, soil and below canopy temperatures showed increasing trend towards the crown periphery revealing the significant canopy cooling effect. Inclusion of higher number of these trees can reduce adverse climatic effects in the semi-arid valley and supplement organic source of nutrients.
Key words: Acacia seyal, Acacia tortilis, Balanites aegyptiaca, microclimate modification, soil amelioration.
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