Woody species composition and soil properties under some selected trees in parkland agroforestry in central rift valley of Ethiopia

Different parkland agroforestry practices conserve diverse woody species in different agroecologies. Despite variation in the extent most multipurpose agroforestry tree species have a positive influence on soil nutrient accumulation. A study was carried out in Shashemene district of central rift valley of Ethiopia to assess the status of woody species composition and topsoil properties beneath canopies of some selected tree species scattered on crop land and open fields, without any tree canopy effect. Woody species composition in the parkland agroforestry inventory was conducted by employing line transect survey method. A total of 36 sample plots/quadrates of 50m by 100m were laid along transect lines with 200m difference between consecutive plots and 1000 m distance between transect lines. On each plot all woody species were counted and recorded. Soil sample were collected from under canopy of Ficus vasta Forssk and Albizia gummifera (J.F.Gmel.) CA. Smith tree and in open field at 30m away from tree trunk. Soil texture, soil pH, available phosphorus, total nitrogen, organic carbon, CEC, and exchangeable base cations were analyzed following standard procedure in National Soil Laboratory and interpreted. Results showed that the presence of 24 woody species representing 15 families and 21 genera at the study site. At the family level, Fabaceae was the most dominant family represented by 5 woody species, followed by Moraceae represented by 4 species.  The average density of 17 stems per ha was recorded from 18ha of land. Soil textural fractions, mainly sands generally decreased under tree canopies compared to open fields. Available P, organic carbon (OC) and total nitrogen contents (TN) of soils were significantly higher under tree canopies compared to the contents in open fields. Soil samples from under canopies of scattered Ficus vasta and Albizia gummifera trees, compared with open fields, generally had higher K and Mg. In general, the studied parkland agroforestry supports high biodiversity conservation and enhanced higher soil nutrient concentration under tree canopies than open fields without trees.