CATION EXCHANGE IN SOILS

Abstract

Base-exchange studies showed that, as with vermiculite, a wide variety of soils have the ability to "fix" alike NH4+ and K+. A large part of the NH4+ and K+ fixation was found to reside in the coarser fraction of the soils associated with vermiculite-like minerals. In replacing adsorbed NH4+ from a soil, it was found that distilling with a base was more effective than leaching with a salt soln. It is recommended that the difference in NH4+ replaced from 2 NH4+-saturated soil samples when distilled with NaOH and with KOH be taken as a measure of the "fixation capacity" of the soil for NH4+ or K+. The differences in the replaceability of adsorbed cations are explained as resulting from their accessibility to the replacing cations, which in turn depends upon the expansible nature of the interlayered crystal lattice space.