Soil Fertility and Nutrient management (1+1)

Calcium and Magnesium availability in soils

Ca &Mg availability in soils:
Ca and Mg are the most abundant cations occupying the exchange sites of the soil colloids of both inorganic (clay) and organic (humus). Soil Ca and Mg mainly come from the weathering of rocks and minerals (Calcite and Apatite). Thus most soils contain enough Ca and Mg except highly weathered leached acid soils and alkali soils. Deficiencies of Ca and Mg most commonly occur in coarse textured soils, acidic soils of high rainfall area due to leaching losses. In soil solution occurs as cations and also adsorbed cation on the clay and humus surfaces and involved in exchange process. The critical limits of exchangeable Ca and Mg vary widely among soils. However average value of <2.0 m.eq/100g for exchangeable Ca and < 0.5 m.eq/ 100g for exchangeable Mg are considered critical limits for availability.

Ca & Mg Transformations:
Ca and Mg occupying the exchange sites of the soil colloids (clay & humus) are subjected to cation exchange reactions with other monovalent and divalent cations then released into soil solution for plants absorption or adsorbed on the clay and organic matter surfaces. Soils usually contain less Mg than Ca because Mg²⁺ ions are not adsorbed as strongly by clay and organic matter as Ca²⁺ ions and further Mg²⁺ ions are more susceptible to leaching than Ca²⁺ions. The solution Ca and Mg is subjected to leaching/erosion losses and crop uptake, thus it may deplete the Ca and Mg content soil.

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