Soil Science

Potassium calcium and magnesium

The so-called "exchangeable bases" (Ca, Mg, K, Na, etc.) are commonly adsorbed on clay minerals and humus in larger quantities than are present in the soil solution. As plants take up the nutrient cations K^+, Ca^2+, and Mg^2+, they expel H^+ ions into the soil solution. This is necessary to maintain electrical neutrality in the plant. The H^+ ions exchange with adsorbed cations, and so more K^+, Ca^2+, and Mg^2+ enters the soil solution ready for uptake. Exchangeable cations constitute a pool of plant-available nutrients, which has some soil organic matter protection against leaching. Weathering of primary minerals and dissolution of secondary minerals in soil also slowly release soluble K^+, Ca^2+, and Mg^2+.

When plant parts die, K+, Ca2+ and Mg2+ are returned to the soil, and cycle back to the absorbed ions pool.

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