An evaluation of methods for the determination of total phosphorus in soils

Abstract

The release of total soil phosphorus from 16 contrasting soils by nitric-hydrofluoric acid decomposition, perchloric acid digestion, and sodium carbonate fusion was compared. The phosphorus released was determined by colorimetric methods, and the values by each procedure were compared with the Lorenz gravimetric method. Pcrchloric acid did not complctcly release the phosphorus from many of the soils even after prolonged digestion. Sodium carbonatc fusion was satisfactory when the melt was extracted with sulphuric acid but not when extracted with water. Two colorimetric procedures were found to be satisfactory. The molybdivanadophosphoric acid yellow method, following nitric-hydrofluoric acid decomposition, and a molybdenum blue method using ascorbic acid as reductant, following sodium carbonate fusion, gave values which agreed closely with those by the gravimetric method following nitric-hydrofluoric decomposition.