Soil Chemical Analysis

Positive ions that are available in soils absorb on grain surfaces. The total sum of cations that can be absorbed bij a soil/sediment at a certain PH is defined by the cation-exchange capacity (CEC, in meq g-1: mol equivalents per gram). The uptake of cations is an important parameter in agriculture and the larger the CEC, the more cations can be absorbed to the soil. The CEC depends highly on the pH of soil and sediments, where the CEC decreases with decreasing PH (increasing acidity). The exchange of ions on sediments occurs commonly fast on geological time scales, but the kinetics of adsorption in natural environments is still poorly understood. The strength of the bonding between the cations and the sediments varies from weak Van der Waals bondings (physical adsorption) to strong chemical bonds. The CEC is widely used for agricultural assessment because it is a measure of general soil fertility as well as an indicator of structural stability because CED is capabel of enhancing development of shrinkage cracks. The list below shows the CEC for different types of minerals. The data indicate that the CEC can vary over 2 orders of magnitude for various types of , minerals and can vary one order of magnitude within one soil type. Cation exchange capacity for different types of sediment (Eisma, 1992; Locher and de Bakker, 1990):

Cation exchange capacity.

Predicting the spatial distribution of soil erodibility factor using USLE nomograph in an agricultural watershed, Ethiopia

Hardpan is a major cause of land degradation that affects agricultural productivity in developing countries. However, relatively, little is known about the interaction of land degradation and hardpans. The objective of this study was, therefore, to investigate soil degradation and the formation of hardpans in crop/livestock-mixed rainfed agriculture systems and to assess how changes in soil properties are related to the conversion of land from forest to agriculture. Two watersheds (Anjeni and Debre Mewi) were selected in the humid Ethiopian highlands. For both watersheds, 0–45 cm soil penetration resistance (SPR, n = 180) and soil physical properties (particle size, soil organic matter, pH, base ions, cation exchange capacity, silica content, bulk density and moisture content) were determined at 15 cm depth increments for three land uses: cultivated, pasture and forest. SPR of agricultural fields was significantly greater than that of forest lands. Dense layers with a critical SPR threshold of ≥2000 kPa were observed in the cultivated and pasture lands starting at a depth of 15–30 cm but did not occur in the undisturbed forest land. Compared with the original forest soils, agricultural fields were lower in organic matter, cation exchange capacity, and exchangeable base cations; more acidic; had a higher bulk density and more fine particles (clay and silt); and contained less soluble silica. Overall, our findings suggest that soil physical and chemical properties in agricultural lands are deteriorated, causing disintegration of soil aggregates, resulting in greater sediment concentration in infiltration water that clogged up macro-pores, thereby disconnecting deep flow paths found in original forest soils. Copyright © 2016 John Wiley & Sons, Ltd.

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Characterization of Degraded Soils in the Humid Ethiopian Highlands

Gully erosion rates and analysis of determining factors: a case study from the semi‐arid main ethiopian rift valley

In Ethiopian highlands, land use changes, mainly, from natural vegetation to cultivated lands brought about rapid nutrient depletion. Intensive and continuous cultivation of land without proper management resulted in decline in soil physical, chemical and biological properties which aggravate crop yield reduction and food shortage. The present study, therefore, is designed to investigate the effects of different land uses on soil fertility status in the Nitisols of Wujiraba watershed. Twenty seven soil samples were collected randomly depth wise (0 - 15, 15- 30 and 30 - 45 cm) from the cultivated, forest and grazing lands. Data were analyzed using the two ways ANOVA in RCBD with three replications. Land use and soil depth showed a significant (P ≤ 0.05) effect on soil physicochemical properties. The highest f (57.8%), OC (4.6%), total N (0.28%), available S (11.1 ppm), CEC (42.2 cmol+ kg-1), exchangeable bases (Ca (22.2), K (0.76) and Na (0.58 cmol+ kg-1)) and available micronutrients ( Fe (14.2), Mn (24.1) and Zn (2.9 ppm)) were recorded on the surface layer of the forest land while lowest pH/KCl(5.03) and highest available P (5.5 ppm) on the surface layer of cultivated land. The results revealed that soil fertility declines as land use changed from forest to grazing and cultivated lands. Hence, it is possible to infer that continuous and intensive cultivation depletes plant nutrients greatly which urge to take measures for maintaining its fertility status of the cultivated soils in the study area.

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Papers

Fertility Status of Soils under Different Land uses at Wujiraba Watershed, North-Western Highlands of Ethiopia