The rapid determination of available phosphate in soil by the coeruleo-molybdate reaction of Denigès

Abstract

1. The coeruleo-molybdate method of Denigès affords a rapid means of estimating phosphates in such dilute solutions as are given by aqueous extracts of soils, 1:5, even when the extract is diluted twenty-fold. 2. High phosphate values were found for bog peats, but the majority of the soils studied gave to the extract phosphate corresponding to under two parts per million of phosphorus pentoxide. Dunged soil gave 20 p.p.m. or more. 3. Extraction for 3–4 hours gives values as high as extraction for 4–7 days with ordinary soils of low phosphate content, but the phosphate of richer soils may undergo a reversion to an insoluble form during prolonged extraction.