Abstract
Clay content and ratios of exchangeable cations are highly dependent on characteristics of soil parent material and deferential effect of weathering/leaching. Calcium (Ca) and magnesium (Mg) contents ofsoils are significantly correlated, and Mg content affects some soil physical characteristics and erodibility. The objective of this study was to establish a relationship between the distribution of clay, Mg, Ca, K and their ratios in some Nigerian soils. A total of 72 profile pits were prepared in 7 locationsdistributed in Niger, Edo, Oyo, Ogun and Osun States in the savanna region of Nigeria. The soils (comprising 49 Alfisols, 16 Entisols, 4 Ultisols, 2 Vertisols and 1 Inceptisol) were formed on shale/limestone, sandstones or basement complex (coarse-grained granites, coarse grained granitegneisses or amphibolites) materials. There was significant correlation among the textural separates (r2 >0.21 < 0.96; p < 0.05 < 0.01), Ca, Mg and K content (r2 > 0.29 < 0.91; p < 0.05 < 0.01) of the soils.Correlation between clay and the ratios of exchangeable cations was significant in two locations (r2 >0.38 < 0.77; p < 0.05 < 0.01). Regression equation established that profile distribution of clay was highlyinfluenced by magnesium content (r2 > 0.73 < 1.00, p
Highlights
The relative levels of cations in the exchange complex are found to be more important than the absolute quantities in relation to crop response (Voortman, 1985), because there is always interactions between Ca, Mg and K
The ratios of the elements could more express imbalances compared to their absolute quantities. This is because, the activites of the cations are largely independent of their total concentrations but on their ratios which are characteristics of the parent material and subsequently soil as the values of these ratios are dependent on their proportions in the parent material and the differential effect of weathering/leaching (Voortman et al, 2002; Olatunji et al 2007) indicating direct relationship between weathering, cation exchange capacity (CEC) and clay
The size of the exchange site is called cation exchange capacity (CEC) which is defined as the measure of negatively charged sites on the clay-humus molecules or the exchange complex which is normally occupied by Ca, Mg, K, Na ions
Summary
The relative levels of cations in the exchange complex are found to be more important than the absolute quantities in relation to crop response (Voortman, 1985), because there is always interactions between Ca, Mg and K. Irrespective of the concentration of other exchangeable cations in the soil, it has been reported that Mg influences clay dispersion proportionately to its concentration in the exchange site (Dontsova and Norton, 2001, 2002, Yilmaz et al 2005) Negative effects of Mg (intrinsic or extrinsic) on soil structure have been established. This is probably as a result of great quantity of hydration energy and subsequently hydration radius of Mg compared to Ca (Bohn, et al 1985). It had been reported that high percentage of Mg
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