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Abstract
The extraction of soil organic phosphorus from Egmont black loam by several acidic and alkaline reagents was determined. The proportion of the total organic phosphorus extracted by acid solutions varied from 3 per cent with 0.1 N HCl to 85 per cent with 10 N H2SO4. There was evidence for some degree of selective extraction by K2CO3 and NH4OH solutions.
The procedure of three serial extractions, each of one hour at room temperature with 0.3M KOH solution, following acid pretreatment, was adopted as the standard extraction procedure. This method extracted 83 per cent of total organic phosphorus. Fractionation of extracted organic phosphorus indicated that about 30 per cent was associated with the humic acid fraction. Fractionation of the acid-soluble phosphorus by fractional precipitation proved unsuccessful.
A partial fractionation of soil organic phosphorus was achieved using a strong anion-exchange resin (hydroxide form). 0.3M KOH soil extracts applied directly to the resin column were separated into three fractions containing: I—humic acid-associated organic phosphorus, IIinorganic phosphorus, III—50–60 per cent of the acid-soluble organic phosphorus. Fractions II and III were nearly colourless.
There was a marked exclusion of organic phosphorus from resin with 8 per cent cross-linking compared with a resin with 2 per cent cross-linking, the relative retentions of organic phosphorus being 1:3.