TEMPERATURE EFFECTS ON POTASSIUM EXCHANGE AND SELECTIVITY IN DELAWARE SOILS

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Abstract
We investigated the effect of temperature on K availability using quantity-intensity (Q/I) analyses and on K selectivity on the Ap and B21t horizons of a Kalmia sandy loam (Tppic Hapludults), an Evesboro loamy sand (Typic Quartipsamments), and a Matapeake silt loam (Typic Hapludults) from the Delaware Coastal Plain. The predominant mineral suite of the <2-μm clay fraction consisted of vermiculite, mica, and chloritized vermiculite, with lesser quantities of kaolinite and quartz. Quantity-intensity analyses revealed that as temperature increased from 0 to 40°C, the amount of K adsorbed by the soils decreased. For similar initial electrolyte concentrations, ΔK (K concentration difference between initial and equilibrium solutions) decreased, while the activity ratio of K+ to (Ca2+ + Mg2+)1/2, or ARk, increased. Thus, to maintain an equal amount of K on the soil as temperature increased, a higher ratio of K+ to (Ca2+ + Mg2+)1/2 in solution was needed. The equilibrium potassium activity ratio (ARek), which is a measure of available K, increased in the soil horizons as temperature increased. The labile K parameter, (ΔK0), changed little with temperature, though the potential buffering capacity (PBCk), which is related to the CEC of the soil, decreased with increased temperature. Potassium selectivity coefficients (kK), based on the Gapon equation, decreased with increased temperature, indicating decreased K sorption relative to Ca2+ and Mg2+, with increased temperature. As temperature increased from 0 to 40°C, the quantity of K in the equilibrium solution increased from an average of 19.3 to 20.9 moles/liter and from 14.0 to 17.0 x 10−4 moles/liter in the Ap and B21t horizons, respectively, of the three soils. The amounts of Ca and Mg in solution, however, decreased as temperature increased.
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