SOIL CHARACTERIZATION, CLASSIFICATION, FERTILITY MAPPING AND PHYSICAL LAND SUITABILITY EVALUATION FOR RAIN-FED PRODUCTION OF MAJOR CROPS AT MUGER SUB-WATERSHED, NORTHERN OROMIA, ETHIOPIA

Abstract

Soil characterization, classification and land suitability evaluation are the main information sources for precision agriculture, land use planning and management. However, the fertility status of the soil and sustainable soil management practices that are based on the understanding of soil system are not available for most part of Ethiopia. On the basis of this fact, a study was conducted in Muger sub-watershed, North Shoa zone of Oromia region, Ethiopia to (i) characterize and classify the soils, (ii) assess the spatial variability of soil fertility status and (iii) evaluate the physical suitability of the land of the sub-watershed for rain-fed agriculture. Three slope classes were considered and eight representative pedons, two each on the upper and lower, and four on the middle slope were described and samples were collected from identified horizons of each pedon for the characterization and classification of soils at the study area. The soils were classified into different Reference Soil Groups following the World Reference Base for Soil Resources (WRB). Twenty-five composite soil samples (0-20cm depth) from three slope positions and from three land uses viz. cultivated, grazing and forest lands were also used for generating spatial data and mapping the status of selected fertility parameters using ordinary. Four major crops (barley, beans, wheat, and Teff) and four land mapping units (LMU1Csc, 2Ascl, 2Csc and 3Bscl) were identified for physical land suitability evaluation. The simple / maximum limitation method was used to evaluate the degree of suitability of the land mapping units. As a result, the pedons showed variability in soil physical, chemical and morphological characteristics. The field as well as the laboratory determinations revealed dominance of sand and the texture ranged from sandy loam to clay both in surface and subsurface layers. The soils showed acidic to neutral reaction (pH 5.59-7.24) and were free of salt (EC<0.5dSm-1). Organic carbon (OC), cation exchange capacity (CEC), and percent base saturation (PBS) of the soils ranged from 0.41 to 4.06%, 26.42 to 60.94 cmol(+)kg-1 and 56.58 to 93.97%, which is rated as very low to high, high to very high and moderate to very high, respectively. The dominance of exchangeable bases was in the order of Ca2+>Mg2+>K+>Na+. The soils were low to high in available P and total N, whereas, the concentrations of micronutrients in the soils were high (Fe), medium (Mn), very low to high (Zn) and low to high (Cu). The soil developed from mollic surface horizon and are classified as Mollic Leptosols (Eutric), Hyperskeletic Leptosols (Clayic) Pellic Vertisols (Grumic), and Rhodic Nitisols (Haplic), according to the WRB. Soil OC varied significantly (p<0.05) across different land uses. The mean values of OC and total N were low for cultivated lands but high for grazing and forest lands. Zinc content was low on cultivated and grazing lands but high for forest land. This indicates that Zn, TN and OC could be the limiting factors for crop growth. On the contrary, CEC, exchangeable Ca2+, Exchangeable K+, and extractable Fe were high in all land uses. However, Cu, PBS, extractable Mn, available P and available sulfur contents were at medium rate for all land uses. Micronutrient content of the studied soil ranged from 57.94-78.42, 6.97-12.37, 2.56-4.45and 0.22-1.31mg kg-1 for Fe, Mn, Zn and Cu, respectively. There were significant (p<0.05) difference among values of sand, silt, OC, TN, Zn, Mn and Av.S on different land uses of the area. These soils, together with landscape attribute and climate, were evaluated for suitability analysis. Based on the land suitability evaluation criterion, from the total xvi area (931 ha) of evaluated land, 33% and 67% of land is moderately and marginally suitable for the considered varieties due to fertility, stoniness and topographic limitations. The overall land suitability evaluation revealed that LMU1Csc with an area of 16% (146 ha) of Muger Sub-watershed was moderately suitable (S2f) for wheat and marginally suitable (S3c, f, s, t) for barley, bean and teff. Land mapping unit 2Ascl, consisting about 30% (276 ha) area extent was moderately suitable (S2f, s) for barley and wheat and marginally suitable (S3c, f, s, t) for bean and teff. Land mapping unit 2Csc, which covers 33 % (309 ha), was moderately suitable (S2c, f, s) for bean and wheat and marginally suitable (S3c,f,t) for barley and teff. On the other hand, land mapping unit designated as 3Bscl and having 21 % (200 ha) was rated as marginally suitable (S3c,f,t,s) for all considered varieties of barley, bean and teff but moderately suitable ((S2c, f, s) for wheat . Accordingly, it can be concluded that soil depth (shallow soil), physical (stoniness and elevation), and soil fertility (low to medium content of OC, TN, Zn, Mn and Av.S) were recorded in the cultivated lands as a limiting factors. Hence, to overcome the identified limitations continuous application of manure and compost practices is essential by the farmers integrating with chemical fertilizer. On the other side at different slope positions showed shallow soil depth; this might be due to soil erosion. Hence, it is advisable to practice a sustainable area enclosure in the upslope area that enhances rate of infiltration, curbing formation of runoff to reduce the detachment of soil. With regard to nutrients deficiency; sulfur, nitrogen, zinc, and phosphorus containing mineral should regularly be applied to the soil in order to replenish the nutrients and reduce the nutrient mining problem.