Mineralization of Soil Organic Phosphorus With Particular Reference to the Effect of Lime

In a laboratory experiment, liming resulted in an average decline of 3.6 per cent in the total organic phosphorus content of incubated surface samples of seven acid soils from eastern Canada. Increases of 2.6 and 5.1 per cent in 1N H 2 SO 4 - and 4N HCl-soluble inorganic phosphorus, respectively, and a decrease of 46.4 per cent in NaHCO 3 -soluble organic phosphorus (pH 8.5) provided further evidence of mineralization of organic phosphorus following liming. There was some evidence, however, that the differences in NaHCO 3 -soluble organic phosphorus following liming were due only in part to mineralization, since Ca(OH) 2 added to a soil just prior to extraction with NaHCO 3 had a repressive effect on the solubility of the organic phosphorus compounds.Some mineralization of organic phosphorus occurred when unlimed samples were incubated in the laboratory for 9 months.Marked increases in microbiological activity, as indicated by increased numbers of microorganisms, and increased CO 2 and NO 3 -nitrogen production, were associated with lower values for extractable organic phosphorus following liming. Partial sterilization of samples with toluene lowered biological activity in the unlimed and limed samples. Toluene was found, however, to have a positive effect on release of phosphorus from organic form.