EFFECTS OF Balanites aegyptiaca (L.) DEL. AND Faidherbia albida (DEL.) A.CHEV ON SOIL PROPERTIES AND AN ESTIMATION OF THEIR BIOMASS CARBON STOCKS IN PARKLAND AGROFORESTRY IN BENA TSEMAY DISTRICT, SOUTHERN ETHIOPIA

Abstract

Manmade climate change has been an existential threat to humanity, and the small-scale agriculture, in particular, worldwide. Trees in farmlands can provide climate regulation services through sequestration of atmospheric carbon dioxide and storing them in their biomass, while also improving soil physicochemical properties and microsite conditions, if properly managed. Yet, the contributions of trees in farmlands toward carbon storage and their impacts on soil properties in agroforestry systems have not been well-understood. Here, we assessed the biomass carbon storage potential of B. aegyptiaca and F. albida in Benna Tsemay District, southern Ethiopia, and studied their effects on soil properties. Carbon stocks in biomasses of the study species were quantified using non-destructive allometric equations based on DBH measurements across farmlands. Additionally, the effects of these trees on soil properties were quantified using a complete randomized block design with five blocks (i.e., farmlands). In each block, separately for each species, three trees of B. aegyptiaca and F. albida having approximately similar height, DBH, and crown diameter were selected. Then, through the origin of each of these target trees, two orthogonal transects were drawn to collect soil samples at three radial distances from the tree trunks (i.e., at 1/3* crown radius m, 2/3* crown radius m, & 3* crown radius m) from a 0-20 cm soil depth. The results showed that the overall mean of biomass carbon stocks and carbon dioxide sequestration of B. aegyptiaca and F. albida were 262±286.7 and 247.2±332.5, and 209.8±317.8 and 246.8±332.2 Kg C ha-1, respectively, across farmlands. Whereas Soil organic carbon, Total nitrogen, Available pospures, Cation exchange capacity, and Soil pH were significantly influenced (p<0.05) by tree radial distances under B. aegyptiaca and F. albida, soil texture was not influenced (P>0.05). Both B. aegyptiaca and F. albida trees seem to store substantial amount of carbon and improve soil properties suggesting the need to retain these species on farmlands. Yet, future studies should focus on determining tree density and size to optimize agricultural benefits