Release of Phosphorus from Insoluble Phosphatic Materials in Acidic Lowland Rice Soils

The release ofphosporus in available form from insoluble phosphatic materials, such as rockphosphate, bonemeal and basic slag and the effect of addition of organic matter on such release were studied in the laboratory in an acid lowland rice soil with a view to explore the possibility of utilizing these comparatively cheap sources of phosphorus as a substitute for superphosphate for growing rice in acid soil.

Results show that within 15 days of application, more than 86 per cent of the phosphorus added as superphosphate was converted to the unavailable form. Both basic slag and rockphosphate always maintained in the soil a higher amount of available phosphorus than superphosphate. Bonemeal, however, behaved as slightly inferior to superphosphate in the matter of supplying available phosphorus in the soil.

Application of organic matter did not bring about any additional increase in the release of phosphorus over that occured in absence of it. Results suggest that rockphosphate and basic slag may be more effective than superphosphate for growing rice in acid soils.