Effects of exchangeable Ca:Mg ratio on the dispersion of soils some southern Nigeria soils.

Abstract

Soil surface sealing and erosion which are the result of soil dispersion can be harmful or detrimental to soil, soil resources and also agricultural production thereby leading to great economic loss. Soil samples were collected at 0-30cm depth in eight locations in southern Nigeria. Dispersion behaviours of soil contents were studied at different Ca: Mg ratios. The range of values of properties determined are as follows; clay 10-22%, silt 1-18%, sand 64-89%, WDC 6-14%, WDS 1-16%, CDR 0.44-0.86%, DR 0.41-0.84%, ASC 2-18%, CEC 4-15.6cmolkg^-1 , percentage base saturation 18-66%, available phosphorus 1.87-34.57mg/kg. The soils studied were acidic, low in nutrient level, showed high dispersion rate, high water- dispersible clay content and the textural class were loamy sand and sandy loam. The exchangeable Ca²⁺ and Mg²⁺ contents of the soils dominated the exchange complex. The cation exchange capacity (CEC) ranges between 4 and 15.6 cmol kg^-1. Values of percentage base saturation are between 18 and 66%. The available phosphorous ranges between 1.87-34.57 mg/kg. The distribution of Ca and Mg varied with the quantity of ratio of CaSO₄ and MgSO₄ added. The higher the proportion of Mg the higher the clay content while a lower Mg proportion had a lower clay content. Secondly, a higher Ca²⁺ proportion resulted to smaller clay content while a lower Ca²⁺ proportion led to a high clay content. From this study it was discovered that high Mg, silt and clay cause soil dispersion which will be detrimental to the soil. Also high CDR and DR are indicators of high soil dispersity. Therefore, monitoring dispersion in soil is important to avoid its negative impact on the soil. Management practices should be applied in the form of application of fertilizer and liming materials to the soil as higher concentration (Ca²⁺and Mg²⁺) will be introduced to the soil which will bring about dispersion in the soil.

Keywords: Dispersion, Ca: Mg ratio, dispersion ratio, clay dispersible ratio, dispersible silt.