Magnesium Forms in Selected Temperate and Tropical Soils

Abstract

A scheme was developed for fractionating soil Mg into exchangeable, organic‐complexed, acid‐soluble, and primary mineral forms. The scheme was tried out on 20 soils from different regions of the world. Magnesium content was influenced by the nature of the parent materials, climate, and age of the soil. There was more Mg in youthful alluvial soils from Southeast Asia as well as loess and till‐derived Illinois soils which had high amounts of 2:1 lattice clays. Highly weathered oxisols from Sierra Leone were low in Mg. In general, within the soils studied, Mg distribution ranked in the following order: Primary mineral > Acid‐soluble > Exchangeable > Organic‐complexed.Oxisols that had very low exchangeable Mg contained appreciable amounts of Mg in the form of Mg‐Al silicates of reduced solubility. Organic‐complexed Mg was very low in all the soils studied.

Evaluation of the magnesium supplying powers of the Nigerian savannah soils

“…Apparently the rate of release of non-exchangeable Mg is too low to adequately meet the crop requirements. With the clay fraction dominated by kaolinite, this is not unexpected (RICE and KAMPRATH, 1968;SALMON and ARNOLD, 1963;MOKWUNYE and MELSTED, 1972;CHRISTENSON and DOLL, 1913;LOMBIN and FAYEMI, 1916). From the evidence gathered from this study, it would seem that Mg deficiency in the Sudan and Sahel savannah zones of the country is already a reality.…”

“…The total Mg content of a soil is a product of its parent materials, state of maturity and the bio-climatic forces in operation (MOKWUNYE and MELSTED, 1972). Among the factors that govern its availability to plants are the total quantity present in the soils, level of soil organic matter (ILEY, 1969) the quantum and quality of the clay fraction (RICE and KAMPRATH, 1968; soil reaction, (ADAMS and HENDERSON 1962; exchangeable cation ratios (DOLL and HOSSNER, 1964;MCCOLLUCH et al, 1957).…”

The Magnesium Status of Some Fiji Soils

“…Mokwunye and Melsted (1972) found that highly weathered soils contained much less total Mg than less weathered soils. A similar pattern was found for the Fiji soils studied.…”

“…This represents the Mg present in nonexchangeable forms associated with silicate clays most probably in the interlayers of chlorites and vermiculites (Baker 1972). Literature values of acid-soluble Mg ranged from 2.5 to more than 500 mmol/kg (Mokwunye and Melsted 1972;Metson 1974). The Fiji soils gave contents of acidsoluble Mg ranging from 13 to 478 mmol/kg constituting 2-60% of total Mg.…”

“…The suspension was centrifuged, and the supernatant was collected. The residue was extracted three times with ammonium acetate (20 mL, 1 mol/L), and the hydrogen peroxide and ammonium acetate extracts combined, made up to 100 mL, and analyzed for Mg (Mokwunye and Melsted 1972).…”