Thermodynamics of K-Ca exchange in soils .1. Effects of potassium and organic-matter residues in soils from the Broadbalk and Saxmundham Rotation I Experiments

The standard and differential thermodynamic properties of K‐Ca exchange in soils from the Broadbalk (Batcombe series) and Saxmundham Rotation I (Beccles series) Experiments were evaluated for selected manurial treatments, using exchange isotherms and calorimetric measurements. The Beccles soil had a greater preference for K than the Batcombe soil in all the comparable treatments (Nil, PK and FYM). In all the soils, enthalpic forces favoured K preference but entropic forces Ca preference; in all but two cases the magnitude of the enthalpic forces were greater, resulting in K preference (positive ‐ΔGo). The ‐ΔHo values of the soils did not vary greatly, and the main cause of variation in ‐ΔGo values was that in ‐TΔSo values. Residual fertilizer K and FYM residues decreased preference for K at both locations, but more so at Broadbalk than at Saxmundham, presumably because of the greater duration and amount of K manuring at Broadbalk. FYM residues had a very complex effect on the exchange characteristics of Broadbalk soil. It is suggested that these differences are caused by the different pH values of the surface soils before they came into arable usage, which reflect their contrasting parent materials and pedogenic histories, and by the different durations and extents of manuring in the two experiments.

RESP-09032