Soil Classification in Yigossa Watershed, Lake Tana Basin, Highlands of Northwestern Ethiopia

Abstract

A study was conducted in 2013 at Yigossa watershed, Northwestern Ethiopia to study the morphological and physicochemical characteristics and classify soils using FAO/WRB criteria. Four soil profiles, at slope classes of 0-2, 2-5, 5-8 and 8-15% were described in-situ using FAO/WRB guideline. Soil samples were collected from pedogenic horizons and analyzed for soil color, bulk density, texture, structure, pH, organic carbon (OC), total nitrogen (TN), available phosphorus (AvP), cation exchange capacity (CEC), exchangeable bases (Ca2+, Mg2+, K+ and Na+) and percent base saturation (PBS). FAO/WRB soil classification legend was used to classify the soils. Geographical Information System (GIS) software was employed to produce slope and soil maps of the watershed. Results of the study indicated that Yigossa soil profile No. 4 and No. 2 (i.e., YSP-4 and YSP-2) were very shallow (< 30 cm) and moderately shallow (50-100 cm), respectively; whereas profile No. 1 and No. 3 (i.e., YSP-1 and YSP-3) were very deep (> 200 cm). Surface soil color was 5YR4/3 for YSP-1 and 2.5YR3/3 for YSP-2 and it was 10YR4/2 and 10YR 2/1 for YSP-3 and YSP-4, respectively. All profiles, except YSP-4, were clay in texture. Highest and lowest bulk density values of 1.48 g cm-3 in YSP-3, and 0.7 g cm-3 in YSP-1 and YSP-4 were recorded. Highest OC (2.3%) and TN (0.2%) were registered at the surface of YSP-3. Highest CEC (36.2 cmolc kg-1) and PBS (83%) were recorded from subsurface horizons of YSP-3. Generally, YSP-1, YSP-2, YSP-3 and YSP-4 were identified as Nitisols, Luvisols, Gleysols and Regosols at 2-5, 5-8, 0-2 and 8-15% slope classes, respectively.