PHYSICO CHEMICAL PROPERTIES of SOIL and WHEAT YIELDS UNDER THE CANOPIES OF Faidherbia albida (Delile) A.Chev and Acacia tortilis (Forssk.) Hayen IN PARK LAND AGROFORESTRY SYSTEM IN CENTRAL RIFT VALLEY, ETHIOPIA

Abstract

Agroforestry is the set of land-use practices involving the deliberate combination of trees, crops and/or animals on the same land management unit in some form of spatial arrangement or temporal sequence (Lundgren and Raintree, 1982). The trees have been used for fuel wood, charcoal, shade, fodder, soil fertility maintenance and fencing. This study was conducted to assess the effect of Faidherbia albida and Acacia tortilis on grain yield of wheat and above ground biomass and 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 Faidherbia albida and four Acacia tortilis trees were purposively selected and soil sample collected from four directions at three distances (1.35 m, 3.35 m and 26.35 m) from tree trunk and composite soil samples was taken for both physic-chemical analyses. As well as average grain yield and biomass taken from each distance were compared between each distance. Collected was analyzed by two way ANOVA and mean separation with LSD (%). Results indicated that recorded grain yield and biomass yield showed significant difference (p < 0.05) and were significantly greater under canopy of both trees at both locations compared to the open land. Mean moisture levels of all sites 1.35 (14.319%) were significantly (p < 0.05) greater than openland (10.795%) at 26.35 m from tree trunk. Bulk density was also significantly affected by tree canopies (p<0.05). It was increased from 1.201 g/cm3 under canopy to 1.286 g/cm3 in the openland. Soil textural distribution (sand% silt% and clay%) was not significantly affected (p>0.05) by distance from trees. At both sites, pH was significantly lower (p < 0.05) under the canopy than out of the canopy (it was lowered 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 compared to openland. Apart from these, the recorded values of exchangeable sodium, potassium and electrical conductivity revealed statistically non-significant difference among the treatments. In general the two trees showed increment of wheat yield and selected soil physico chemical properties under their canopy as compared to the open land