Properties of clays and soils after acid treatment. II. Urrbrae fine sandy loam

Abstract

Treatment of the soil with acids led to dissolution of aluminium which in the case of nitric acid remained in solution or as exchangeable aluminium. Thus the pH remained low, and the soils retained a positive charge for up to 40 weeks, resulting in flocculation of clay and some stabilization of aggregates with diameters >0.5mm. With phosphoric acid the dissolved aluminium was precipitated presumably as a complex phosphate which functioned as a cement within soil aggregates. The precipitation of the aluminium led to a more rapid rise in pH, compared with nitric acid treated soils. Negative charges in phosphoric acid treated soils were initially reduced, but within several weeks recovered to the same levels as in untreated soils; or even higher for a short period. The water-stable aggregation resulting particularly from the addition of phosphoric acid led to higher porosities and water-holding capacities, but lower bulk densities. The porous aggregates were mechanically weaker than those from untreated soils.