Soil organic phosphorus

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).