Soil organic phosphorus

Abstract

The extraction and resin fractionation procedures for soil organic phosphorus developed in Part I were applied to a representative group of New Zealand soil types (18 soils). The amount of organic phosphorus extracted varied (59–87 per cent of total organic P, mean 75 per cent), but no clear pattern was evident. The binding of inorganic and organic phosphorus in the soil were evidently distinct processes, the organic phosphorus being more readily extractable by dilute KOH. Essentially the same pattern was found for all soils for the resin fractionation of the 0.3M KOH extracts. The organic phosphorus was split into humic-associated organic phosphorus and acid-soluble organic phosphorus, both fractions being separated from inorganic phosphorus. The much higher retention of organic phosphorus on resin with 3 per cent cross-linking compared with 8 per cent cross-linking was also found for all soils. Analysis of soils from no P and high P plots from a phosphate fertiliser field trial indicated that the extraction and fractionation procedures would be valuable for following the transformation of fertiliser phosphorus into soil organic phosphorus in long-term trials but would not be suitable for following short-term trends. Lines of investigation developing from the present work are discussed.