Potassium Leaching in Soil Column Experiment By Surface Application of Gypsum.

Gypsum (CaSO₄.2H₂O) has been applied to sodic and degraded soils to improve soil structure and other physico-chemical properties. It also provides Ca⁺² and SO₄^-2 as plant nutrients and, ameliorates subsoil acidity by displacing acid causing cations. There is very limited information on the displacement of K⁺ from soil colloids that are amended with relatively high concentration of gypsum. Hence, a displacement study on leaching of K⁺ was conducted under unsaturated steady state flow conditions on sandy loam and sandy clay loam soil in columns that are 7 cm in diameter and 30 cm long. The two soils were equilibrated with 0, 10, 25 and 50 mM K⁺ at a rate of 1 mL per minute and, then the soil columns were leached with 5.2 mM gypsum at the rate of 1 mL per minute. This study showed that gypsum displaced significant amount of K⁺ from both sandy loam and sandy clay loam soils and, the rate of displacement per pore volumes of soil increased as K⁺ treatment concentration increased.  As expected, K⁺ leaching rate for the sandy loam soil was greater than the sandy clay loam and reached equilibrium at shorter time. In general, heavy application of gypsum has a potential to leach not only acidic cations, but also K⁺ and other agronomically important similar cations especially on coarse textured soils.