THE SOIL RESOURCES OF HINTALO WAJERAT DISTRICT, NORTHERN ETHIOPIA: SURVEY, QUALITY, EROSION RISK ASSESSMENT AND LAND SUITABILITY EVALUATION

Abstract

Soil survey and land evaluation are pertinent for effective utilization of natural resources and deliver site-specific soil management recommendations to the end-users. There is, however, limited information on the properties, constraints and potentials of soil resources in Hintalo Wajerat district of Northern Ethiopia. The purpose of this study was to (1) characterize, classify and map soils (2) generate soil quality index and analyze its spatial distribution (3) assess and map soil erosion risk; and (4) evaluate physical land suitability for rain-fed agriculture in Hintalo Wajerat district of Northern Ethiopia. A land unit map produced by overlaying geology, landform and land use/cover map of the area was used as a guide for soil surveying. A land unit legend with 22 units was generated and hence, twenty two profile pits were dug and characterized. Soil samples collected from each pedogenic horizon were considered for standard laboratory analysis. Total data set (TDS) and minimum dataset (MDS) indicator selection approaches were used to generate soil quality index (SQI) of top soils (0-30 cm) and subsoils (30-60 cm). A linear scoring function followed by weighted additive integration method was used to calculate indices. For soil erosion risk modeling, a 30m x 30m pixel-based spatial distribution of sheet and rill-based erosion and deposition rates was analyzed using the USPED (Unit Stream Power Erosion Deposition) model. Fuzzy set model, analytical hierarchy process (AHP) and geographic information systems (GIS) were integrated for generating land suitability map of different land utilization types. Black (10YR2/1) to yellow (10YR7/6), mottle free, soft to extremely hard and nonsticky/nonplastic moderately effervescent containing very few fine roots and few biological activities shallow to very deep soils were found. The soils had fine to moderate granular/crumb surface grading to blocky subsurface structures, very few to abundant coarse fragments ranging from fine gravels to stones. The soils were loamy sand to clay, moderately porous, neutral strongly alkaline, nonsaline, calcareous containing below targeted levels of soil organic carbon (SOC), total nitrogen (TN) and available phosphorus (AP) but rich in exchangeable bases, cation exchange capacity (CEC) and percentage bases saturation (PBS). Results revealed the presence of pedogenic processes of melanization, cumulization, eluviation, illuviation, vertization and calcification owing to developments of ochric and mollic surface and camibic, calcic, petrocalcic and vertic subsurface horizons. Haplic Eutric Leptosols, Hyperskeletic Mollic Leptosols, Skeletic Leptic Cambisols, Akroskeletic Mollic Cambisols, Eutric Leptic Cambisols, Leptic Mollic Cambisols, Haplic Mollic Cambisols, Haplic Eutri Cambisols, Chromic Mollic Cambisols, Mollic Vertic Cambisols, Eutric Vertic Cambisols, Eutric Pellic Vertisols, Pellic Calcic Vertisols, Hypocalcic Vertic Calcisols, Hypocalcic Luvic Calcisols and Vertic Petric Calcisols soil units were identified. Typic Ustorthents, Lithic Ustorthents, Typic Haplustepts, Typic Humustepts, Lithic Calciustepts, Typic Haplusterts, Petrocalcic Calciusterts, Vertic Haplocalcids, Ustertic Calciargids and Calcic Petrocalcids were their xvii taxonomic classes. SQI of the soils varied from 0.38 to 0.65 on the top soils and 0.41 to 0.61 on sub-soils using the TDS and 0.51 to 0.90 on top soils and 0.43 to 0.66 on sub-soils using the MDS showing higher records on top soils than sub-soils. On top soil, soils having very low, low, moderate and high soil quality levels accounted for 3.41%, 25.93%, 63.95% and 6.71% of the area when TDS approach was used while moderate, high and very high soil quality levels with the respective proportion of 37.4%, 52.38 and 10.23% was obtained based on MDS approach. The values on the sub-soils was in the range of low (50.67%) to moderate (49.33%) when total data set was used and low (10.54%), moderate (88.02%) and high (1.45%) when MDS approach was used. Soil erosion-deposition analysis results showed a soil loss rate ranging from 0 to 72.6 (12.4 on average) t ha-1 yr-1 and deposition rate from 0 to 60.0 (on average 7.3) t ha-1 yr-1. Of the total area, 57% (551.60 km2) is under stable erosion and deposition risk levels; 14% (129.03 km2) lies under moderate to very severe erosion risk levels; 10% (48.90 km2) faces slight and very slight erosion risk levels; <0.2% (1.28 km2) experienced severe and very severe deposition rate; 7.1% (68.89 km2) faces moderate deposition and the remaining 6.8% (65.98 km2) and 5.3% (51.35 km2) is under slight and very slight deposition risk levels. Soil loss was severe (with very limited deposition rate) in steep lands under cultivation with Leptosols soil units while Vertisols on level land were with low risk of erosion and high deposition rate. Results of the suitability analysis showed that 37.59%, 56.99% and 5.42% of the area were moderately suitable (S2), marginally suitable (S3) and currently not suitable (N1) for production of teff respectively. For wheat cultivation, 14.77%, 67.82% and 17.42% of the area falls under S2, S3 and N1 respectively. For barley production, 60.91%, 35.14% and 3.96% respectively were moderately, marginally and currently not suitable. It’s 30.54%, 36.17%, 18.05% and 15.24% were grouped under S2, S3, N1 and N2 suitability levels respectively for sorghum production. The area extent for S2, S3 and N1 is 49.30%, 76.76% and 71.21%; 24.80%, 19.87% and 18.86% and 25.90%, 3.37% and 9.93% for faba bean, chickpea and lentil crops respectively. Pedogenic processes and soil properties varied with lithology, landscape positions and landuse/cover types resulting in soil units requiring different management approaches. Slope gradient, length of growing period, available water capacity, mean weight diameter, total nitrogen, available phosphorus and soil organic carbon content were found the main crop production limiting factors of the area. Acidifying fertilizers, grazing and water management activities are needed to recover soils of the district and boost their agricultural service value. Leptosols with steep slopes under intensive cultivation and grazing are in demand of special attention.