Soil Fertility in Koka Nagawo Area of Lumme District in East Shoa Zone of Oromia Region, Ethiopia
For designing proper soil fertility management interventions, locally specific information on physical, chemical, and biological properties of soils is indispensable. Therefore, a study was conducted to assess the spatial variability in the fertility status of soil of Koka Nagawo area of Lumme District in East Shoa Zone of Oromia Regional State, Ethiopia, based on selected soil physico-chemical properties. Eleven land units were delineated and mapped based on their soil color, slope, drainage, and soil management practices which were assumed to cause variability in soil fertility status among the land units. Eleven composite surface (0-20 cm) soil samples were collected randomly from each land unit and selected soil physico-chemical properties determined in the laboratory. The results of the study revealed that the soils of all land units on rain-fed agriculture (land units 1, 2, 3, 7, 8, and 11) had a clay loam texture but the soil of all land units on irrigated agriculture in floodplain (land units 4, 5, 6, 9, and 10) had a clay texture. The highest bulk density (1.38gcm-3) was recorded for land units 1 and 3 and the lowest (1.16gcm-3) was recorded for land units 4 and 10. The percent total porosity of all the land units was found to be very high. The pH values ranged from slightly alkaline to moderately alkaline for all land units. Land units 4 and 10 had high organic matter contents and land units 5, 6, 7, 8, and 9 had moderate organic matter contents whereas the remaining land units had low organic matter contents. Available P contents of the soils from land units 1, 2, 3, 7, 8 and 11 were medium whereas those of the soils from land units 4, 5, 6, 9, and 10 were high. The cation exchange capacity of the soils of the area ranged from 28.66 to 52.26 cmol(+)/kg soil, which is rated as high and very high, respectively. Exchangeable Ca was very high in irrigated floodplain land units but high in land units of rain-fed agriculture. Exchangeable Mg was high in the land units 4, 5, 6, 9 and 10, medium in land units 7 and 8, low in land units 1, 2, and 11, and very low in land unit 3. All the land units of the area revealed very high exchangeable K contents. Exchangeable Na contents of soils were high in all land units except for land unit 8, which was medium. The values of percent base saturation ranged from high to very high except for land unit 3 which was medium. Generally, the extractable micronutrient cations (Cu, Zn, Mn, and Fe) contents of the soils were found to be at critical levels, below which crops may suffer from deficiency of the nutrients, and low for all land units except land unit 7 which had a high Fe content. The soils of the study area showed potentially rich physical fertility and exchangeable bases except for Mg in some land units of rain-fed agriculture but poor chemical fertility such as alkalinity and low availability of most of the micronutrients. In addition, all land units of rain-fed agriculture low contents of soil organic matter and total N except land units 7 and 8. It could be concluded that the soils of the study areas have no limitation in terms of physical condition as well as availability of cations, but are constrained by low contents of micronutrients and soil organic matter. Therefore, soil fertility management practices in the areas should focus on improving mitigating the high soil pH and increasing the availability of micronutrients and the content of soil organic matter.
Keywords: Floodplain; Physico-chemical Properties; Soil Fertility Assessment
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