POTASSIUM FIXATION IN DUTCH SOILS

Abstract

Potassium fixation, the phenomenon by which K ions are bound with such strength by the soil that they cannot be freed by cations of buffered salts of approximate neutrality, is caused in Dutch soils by a variety of illite with open lattices, which are contracted by entrance of K ions between the layers. The < 2[mu] separate from Dutch soils may contain up to about 80% of this clay mineral, which has been named ammersooite, in honor of the potash experimental field at Ammersooien, where the K-fixing phenomenon was first observed in Dutch soils. The lattices of ammersooite, which have a basal spacing of 15.6 A., are further contracted by NH4, Rb, and Cs ions to that of common (Fithian) illite, 10.8 A. They are not contracted by H+(H3O+), Li+, Na+, Mg++, Ca++ Sr++, and Ba++ which have a smaller polarizability per valence unit. Neither are they contracted by diethyl, dimethyl, or trimethyl ammonium ions. These ions are highly polarized, but are too large for the hexagonal spaces between the layers. Ammersooite may also occur in soils from Belgium, France, and Surinam having a high K-fixing capacity. The entrance of K ions into the layers may be blocked by Fe(OH)3, A1(OH)3, or difficultly exchangeable Fe+++ and Al+++, as was found in a French soil. The blocking can be eliminated by treating the clay separate with dilute KOH or NaOH solution.