Exchange properties and mineralogy of some soils derived from lavas of lower o old red sandstone (devonian) age. I. Exchangeable Cations

Abstract

The cation-exchange properties of three freely drained and three imperfectly drained brown forest soils developed on volcanic parent material in east-central Scotland have been investigated. Samples representative of the A (or S), B and C horizons were separated by exhaustive sedimentation and sieving into clay (<2 μm) silt (2–20 μm), fine sand (20–200 μm) and coarse sand (200–2000 μm) fractions. The cation-exchange capacity (C.E.C.) of the clay ranges from 24 to 65 me/100 g, that of the silt from 11 to 57 me/100 g, that of the fine sand from 2 to 46 me/100 g and that of the coarse sand from 1 to 36 me/100 g. The non-clay fraction of the soils usually contributes more to the total soil C.E.C. than does the clay. From individual exchangeable cation determinations on each separate, the main sources of exchangeable calcium and magnesium in the soil are the sand and silt fractions, whereas the exchangeable potassium is associated mainly with the clay fractions. Leaching of the separates with 0.1 M hydrochloric acid releases more non-exchangeable calcium and magnesium from the sand than from either the silt or clay fractions.