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Determination and Isotope‐Ratio Analysis of Different Forms of Nitrogen in Soils: 5. Fixed Ammonium
Author(s) -
Silva J. A.,
Bremner J. M.
Publication year - 1966
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1966.03615995003000050017x
Subject(s) - ammonium , chemistry , nitrogen , soil water , organic matter , residue (chemistry) , environmental chemistry , inorganic chemistry , soil science , organic chemistry , environmental science
A method of determining fixed ammonium in soils is described. The soil sample is treated with alkaline KOBr solution to remove exchangeable ammonium and organic nitrogen compounds, and the residue is washed with 0.5 M KCl and shaken with 5 N HF:1 N HCl for 24 hr, the ammonium released by the HF‐HCl treatment being determined by steam distilling the soil‐acid mixture with KOH. The KOBr treatment effects almost quantitative removal of organic soil nitrogen under conditions which preclude fixation by soil minerals of ammonium released from soil organic matter by this treatment, and evaluation tests indicate that the procedure used to estimate fixed ammonium in the KOBr‐pretreatment residue is satisfactory. The method is simple and precise, and it has none of the observed defects of previous methods of estimating fixed ammonium in soils. It gives higher values than the Dhariwal‐Stevenson, Bremner, and Mogilevkina methods, and lower values than the Rodrigues and Schachtschabel methods. A modification in which the HF‐HCl treatment is performed at 100C for 30 min is described.