FLORISTIC COMPOSITION OF HOMEGARDEN AGROFORESTRY SYSTEM AND EFFECT OF INDIGENOUS TREE SPECIES COMPONENT ON SELECTED SOIL PHYSICOCHEMICAL PROPERTIES IN HABRO DISTRICT, OROMIA REGIONAL STATE, ETHIOPIA

Abstract

Homegardens are one of the most important niche in which farmers feel confident to plant and maintain tree and shrub species. Homegardens floristic composition and its indigenous tree species that are used for soil fertility improvement in western Harerghe in general and Habro district have not been given much research attention. The study investigated the floristic composition of the homegarden agroforestry system in 36 homegardens, and assessed the effect of indigenous tree species components of the system on selected soil physicochemical properties. The study was carried out in Habro district at three sites (Melka Belo, Haro Chercher and Lega Bera). Soil samples were collected from under Cordia africana and Faidherbia albida canopy and outside canopy at three distances (at half of the canopy radius under the tree, at canopy edge and at three times canopy radius away from the trunk outside the canopy) within the 0-20cm and 20 to 40cm soil depths. A total of 77 plant species were recorded from homegardens of the study area. The families Fabaceae, Solanaceae and Euphorbiaceae were the most diverse, each having nine, seven and five species. The most abundant woody species in the study area were Catha edulis, Coffea arabica and Cordia africana where as the most abundant herbaceous species were Lycopersicon esculentum, Capriscum spp and Nicotina tabacum. The highest species richness (40 woody and 19 herbaceous) was recorded at Haro Chercher site for both woody and herbaceous species and lowest number of species was recorded at Melka Belo. According to Jaccard’s and Sørensen’s similarity indices Melka Belo and Haro Chercher HAgFS (69.23 and 81.82) were the most similar pairs followed by Melka Belo and Lega Bera (61.54 and 76.19) while Haro Chercher and Lega Bera (52.70 and 69.03) were the most dissimilar pairs. Mean total nitrogen, available phosphorus, available potassium and organic carbon were significantly higher under the tree canopy than outside the canopy area (P>0.05). Bulk density was significantly higher at subsurface than surface soil while organic carbon was significantly higher at surface soil than subsurface soil. The analysis of variance revealed that moisture content, soil texture and soil pH were not significantly affected by tree species, distance from the tree trunk and by soil depth. The present study demonstrates that Cordia africana and Faidherbia albida tree that were planted or maintained in HAgFS of Habro district improved soil properties and they can be used as an economically feasible, environmentally friendly and sustainable alternative to maintain soil fertility of the resource poor farmers in similar agro-ecological conditions. Hence, the research encourages agroforestry systems that are found to have positive effects on plant diversity and soil physical and chemical properties when compared to monocropping system. The people of the study area largely cultivate homegarden species, which have market values like Catha edulis and Coffea arabica and depend on this resource for the household cash income.