A PARTIAL FRACTIONATION OF ALKALI‐solUBLE SOIL ORGANIC PHOSPHATE

Abstract

SummaryA study has been made of the precipitation of soil organic phosphates from alkaline extracts. Acidification to a pH of about 0.4 or below precipitated a small and constant proportion of the extracted organic phosphate. Above pH 0.4 there was an increase in the precipitation up to a pH of about z to 3. The proportion of the phosphate brought down at pH 2.9 could in some cases be increased by prior addition of aluminium sulphate, but in no case did this affect the proportion precipitated at pH 0.2. There was marked precipitation of orthophosphate above pH 3, in the presence of excess aluminium, but below pH 3 it was negligible.Inositol hexaphosphate and DNA were precipitated virtually quantitatively at pH 2.9 in the presence of added aluminium even if the extract was incubated before precipitation. Precipitation of RNA was not complete and could be prevented entirely by prior incubation of the extract. At pH 0.2 DNA was precipitated, but not inositol hexaphosphate. Less than half of a freshly purified sample of RNA was brought down, and no precipitation occurred if the RNA was allowed to stand overnight in alkaline solution before acidification.The soil phosphate esters have been divided into three main classes: an acid‐insoluble fraction precipitated at pH 0.2, and two acid‐soluble fractions, one of which is precipitated at pH 2.9 in the presence of excess aluminium, while the other remains in solution. Part of the acid‐insoluble fraction was readily mineralized during incubation in dilute sodium hydroxide, and some hydrolysis is likely during extraction of the soil with this solvent.