Potassium retention and release in Rothamsted and Saxmundham soils

The retention and release of K from ‘No K ’and K‐treated soils from the Rothamsted Classical Experiments and Saxmundham Experiment were examined using K‐Ca exchange equilibria and the kinetics of K release to Ca‐saturated resin. Free energies and enthalpies of Ca→K exchange showed that Saxmundham soils had the greater preference for K, and that residual K from long‐term manuring significantly decreased K binding strength and preference. K release kinetics showed that residual K increased the rate of K release chiefly from the ‘surface’ region, and the amount of K released from ‘surface’ and ‘peripheral’ regions of 2:1 layer silicates in soils. The increased K release from ‘peripheral’ regions of K fertilised soils, together with their decreased K preference, was associated with slowly reversible K fixation on the weathered periphery of 2:1 layer silicates.

RESP-08324