Release of ammonium and organic matter from soil by hydrofluoric acid and effect of hydrofluoric acid treatment on extraction of soil organic matter by neutral and alkaline reagents

Abstract

1. The effect of treating mineral soils with hydrofluoric acid to decompose clay minerals on the extraction of soil organic matter by alkaline and neutral reagents has been investigated. 2. It was found that treatment of soil with hydrofluoric acid had little effect on the extraction of organic matter by alkaline or neutral reagents, but that it released considerable amounts of ammonium and organic matter. More than 90% of the nitrogen in Rothamsted soils was dissolved by repeated treatments with dilute solutions of hydrofluoric acid and sodium hydroxide. 3. It is shown that treatment of clay minerals with n-HF:n-HCl solution at room temperature for 24 hr. effects quantitative release of fixed ammonium from clay minerals and that similar treatment of soil is not likely to cause significant decomposition of organic nitrogen compounds to ammonium. It is suggested that a method based on this treatment may prove useful for the determination of fixed ammonium in soil. Results obtained by this method indicated that 4–8% of the nitrogen in surface soils and 19–45% of the nitrogen in subsoils examined was in the form of fixed ammonium. 4. It is concluded that some mineral soils contain a significant quantity of ammonium and organic matter intimately associated with clay minerals and that this clay-bound material is not dissolved by neutral and alkaline reagents used for the extraction of soil organic matter, but is released by hydrofluoric acid.