ABSTRACT
This chapter describes several methods used for the determination and characterization of
total phosphorus (Pt) and organic phosphorus (Po) in soils.
Determination of the Pt in soil requires the solubilization of P through the decomposition
or destruction of mineral and Po containing materials in the soil. Historically, the two most
widely recognized procedures for the determination of soil Pt are the sodium carbonate
(Na2CO3) fusion method and the perchloric acid (HClO4) digestion method (Olsen and
Sommers 1982). Currently, neither method is widely used in studies involving the determination
of soil Pt. Although the Na2CO3 fusion method is considered the most reliable procedure for
quantitative determination of Pt in soils, it is laborious, tedious, and generally unsuitable for the
analyses of large numbers of samples. Digestion with HClO4, although more adaptable as a
routine laboratory procedure, requires the use of fume hoods specifically designed for the HClO4 digestion. The potential danger of explosions, due to HClO4 buildup or reaction of HClO4 with
organic materials, has led many institutions and laboratories to discontinue the use of HClO4 digestions. Given the greater applicability of the HClO4 digestion method as a routine laboratory
procedure for the analysis of a large number of samples, this procedure has been included in the
current text. The reader is referred to the previous edition of this text (O’Halloran 1993) or Olsen
and Sommers (1982) for details on the Na2CO3 fusion method. Three additional methods for the
determination of Pt in soil are presented in this chapter. One involves the alkaline oxidation of
the sample using sodium hypobromite (NaOBr)=sodium hydroxide (NaOH) (Dick and Tabatabai 1977) and the other two are wet acid digestion procedures using either sulfuric
acid (H2SO4)=hydrogen peroxide (H2O2)=hydrofluoric acid (HF) (Bowman 1988) or H2SO4=H2O2=lithium sulfate (Li2SO4)=selenium (Se) (Parkinson and Allen 1975).
