Soil organic phosphorus

Abstract

The fractionation of the organic phosphorus extracted from five New Zealand soils, studied with microgramme quantities of organic P (Part III of this series — Martin 1964b), was repeated with milligramme quantities. The three fractions, isolated from the anion-exchange resin columns by the original methods, were further sub-divided. Five fractions were separated, fraction 2 containing inorganic phosphorus and fractions 1, 3, 4, and 5 containing only organic phosphorus. Fraction 1 phosphorus, associated with humic acids, was not studied. Thin-layer chromatography showed that for each soil, fraction 4 contained inositol mono- + di-phosphates (range 1% to 7% of total soil organic P), and fraction 5 contained inositol penta-/hexa-phosphates (range 4% to 42% of total soil organic P). No other phosphorus esters were detected in these fractions. Examination of fractions 3 by these methods failed to reveal identifiable compounds. Inositols isolated after hydrolysis of the phosphate derivatives were identified by paper chromatography and electrophoresis. Myo- and “DL”- inositols were present in the five soils in a nearly constant ratio (myo- : “DL”- = 1.8 to 4.0 : 1).