The role of on-farm tree based agroforestry practice in reduction of soil erosion, conservation of water and organic matter is significant. Conservation and enrichment of organic matter in the system can increase the activity of microbes in the soil which assists for better nutrient recycling and thus enhancing soil fertility. The objectives of this  study was to evaluate the effects of Albizia gummifera on-farm tree species on selected soil properties in midland agroecology of Guji Zone, Southern Ethiopia. To achieve these objectives, a total of twenty four composite soil samples were taken from three horizontal distances from surface soil at one depth (0-15cm).Analysis of variance and treatments separation were made by using Tukey’s honest significance difference at 5% probability level. Soils under Albizia gummifera tree canopies were found to contain significantly higher(p<0.05) soil organic carbon, total nitrogen, available phosphorus, soil pH, cation exchange capacity and exchangeable potassium than those outside the canopies. However, in terms of  soil texture significance differences (p<0.05) were not observed between under tree canopies and in open fields.  This study also showed that, the recorded soil bulk density in open fields was significantly higher (p<0.05) than under tree canopies. The current study also indicated that fertility of the soils gradually decreased with the distance away from the tree trunk. Therefore, Albizia gummifera tree species have significant impact on soil physical and chemical properties. Hence, retaining  Albizia gummifera  tree on farm lands of the study area and elsewhere having similar agroecology is paramount importance for soil fertility enhancement so as to improve crop productivity. Moreover, further study on soil microbial population associated with Albizia gummifera tree  such as mycorrhizal fungal and rhizobial species associations and investigation of its leaves nutrient content is needed. 

Key words:  Albizia gummifera, On-farm tree, Open fields, Soil properties, Tree canopy