Evaluation of some wet digestions methods for reliable determination of total phosphorus in Australian soils

Four common wet digestion methods have been evaluated for reliable determination of total phosphorus (P) concentrations in soil samples. Wet digestion of soil samples with nitric acid gave the highest recovery of total P concentrations with a percentage recovery of 90.1 ± 0.9% (n = 3). A lower percentage recovery of 87.0 ± 1.4% (n = 3) was achieved by wet digestion of soil samples with sulphuric acid. The use of acid mixture or acid–alkaline mixture for wet digestion of soil samples gave phosphorus recoveries of 82.4 ± 1.9% (n = 3) and 85.4 ± 2.1% (n = 3) with nitric acid–sulphuric acid mixture and nitric acid–potassium persulphate mixture, respectively. Substantial improvement in phosphorus recoveries with wet digestion of soil samples with sulphuric acid was achieved by further treatment of digested soil samples with sulphuric acid, resulting in a recovery of 92.8 ± 1.0% (n = 3), which was higher than possible with other acid and mixtures. The wet digestion of soil samples with sulphuric acid was also the only method which met reactivity and safety considerations. The successful utilisation of wet digestion with sulphuric acid for reliable determination of total P concentrations in a range of soil samples from some Australian dairy and beef rearing pastoral land is reported.

► Highlights critical importance of suitable digestion for reliable total phosphorus in soil analysis
► Wet digestion of soil samples with sulphuric acid was most reliable.
► Added advantages of using sulphuric acid include moderate reactivity and safety considerations.
► Successful application of method for total P determination in Australian soil samples