THE COMPARATIVE PHYSICAL CONSTITUTION OF WATER-STABLE GRANULES AND OF THE ORIGINATING SOIL

Publisher Website
Google Scholar
Abstract
Water-stable granules were separated from the A1 horizon of 11 Pennsylvania soil types represented by 15 forested and cultivated areas. A complete mechanical and organic-matter analysis was made of the "hand-picked" granules and of the whole soil. Conclusions:[long dash]In the majority of instances large stable granules contain a greater % of organic matter and clay than does the whole soil from which they were derived. The increase in clay content of the granules is not offset by an equivalent decrease in any other single particle size fraction. The % of silt, sand or gravel in the granules thus may be decreased. The stability index, which is a measure of granule stability, is closely correlated with the organic and the clay contents of the soil. The probable permeability is closely correlated with organic content but bears an insignificant relationship to the clay content. Cultivation (broadly speaking) disperses existing granules, and the dispersed clay reaggregates to form granules higher in clay and organic content than the whole soil from which they were obtained. The granules in young soil profiles seem to be formed and stabilized largely through the action of organic and biologic influences. Those in poorly drained profiles are formed chiefly by disintegration of more massive structural units and stabilized by the action of organic matter, whereas those in well-drained mature profiles, provided the latter have easily dispersible clay, possess granules which were formed by dispersion and re-aggregation of the clay and the organic matter. The granule genesis in the Hagerstown, Montalto, and Chester series may have been effected by the cementing action of hy-drated iron oxides when the soil was developing. These granules are present in the forest soil but are gradually dispersed when the soils are brought under cultivation.