Hostname: page-component-cd9895bd7-lnqnp Total loading time: 0 Render date: 2024-12-25T06:18:07.758Z Has data issue: false hasContentIssue false
  • English
  • Français

A new method for the determination of total phosphoric acid in soils

Published online by Cambridge University Press:  27 March 2009

J. G. Shrikhande
J. G. Shrikhande
Affiliation:
Tea Research Institute of Ceylon, Talawakelle
Get access Rights & Permissions [Opens in a new window]

Extract

McLean's shorter method of H2SO4-HNO3 digestion of the soil for total P2O5 failed on some red soils from Ceylon, although Hall's HC1 method gave satisfactory results. The cause of failure of the McLean method was interference by the larger quantities of various bases extracted by H2SO4-HNO3.

After first separating the total phosphoric acid as ferric phosphate, McLean's method produced results closely agreeing with those obtained by Hall's method. Total phosphates were separated by first neutralizing the acids in the soil digest and then precipitating the HC1 solutions of the neutralized product by sodium acetate and acetic acid. On boiling, all the phosphoric acid in the soil extract was separated as ferric phosphate. HNO3 solution of this ferric phosphate when precipitated in the usual way gave a clean yellow precipitate of ammonium phospho-molybdate.

H2SO4-Se served as a good substitute for H2SO4-HNO3 in soil digestions and the results obtained were substantially the same as by Hall's method or by the modified McLean's method. H2SO4-Se digestion has certain advantages, such as the possibility of determining both nitrogen and phosphoric acid on the same soil digest.

When selenium is used as catalyst and the phosphate separated by ammonium acetate and acetic acid, the HNO3 solution of total phosphates produces a white precipitate of a complex ammonium selenito-molybdate along with ammonium phospho-molybdate when precipitated by ammonium molybdate. This defect was eliminated after replacing ammonium acetate by sodium acetate.

Attention is drawn to the unexpected behaviour of selenium compounds of phosphoric acid formed during soil digestion towards the reagents used for precipitating total phosphates.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 32 , Issue 4 , October 1942 , pp. 406 - 412
Copyright
Copyright © Cambridge University Press 1942

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFEEENCES

Agricultural Educational Association (1931). Analysis of Soils Sub-Committee. Agric. Prog. 8, 134.Google Scholar
Ashton, F. L. (1936). J. Agric. Sci. 26, 239.CrossRefGoogle Scholar
Eden, T. (1935). Bull. Tea Ees. Inst. no. 14, 3.Google Scholar
Gunning, J. W. (1889). Z. anal. Chern. 28, 188.CrossRefGoogle Scholar
Hall, A. D. (1921). The Soil, p. 165.Google Scholar
Mclean, W. (1936). J. Agric. Sci. 26, 331.CrossRefGoogle Scholar
Mellor, J. W. (1930). A Comprehensive Treatise on Inorganic and Theoretical Chemistry, 10, 836.Google Scholar
Richards, M. B. & Godden, W. (1924). Analyst, 12.Google Scholar