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Agronomy Journal Abstract -

Colorimetric Determinations of Exchangeable Ammonium, Urea, Nitrate, and Nitrite in a Single Soil Extract1,2


This article in AJ

  1. Vol. 69 No. 1, p. 49-53
    Received: May 17, 1976

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  1. Arthur Onken and
  2. Herbert D. Sunderman3



Interest in N transformations in soils has increased greatly in recent years, particularly with increased use of urea-containing fertilizers. However, only one procedure for determination of exchangeable ammonium, nitrate, nitrite, and urea in a single soil extract has been proposed and it requires the use of both distillation and colorimetric equipment. It would be useful to have a set of colorimetric procedures for the determination of these N forms in a single extract. Previous research indicated sodium sulfate, as an extractant, would be least likely to produce unwanted interferences in these procedures. Thus, research was initiated to determine (i) if Na2SO4, could be used as an extractant for exchangeable NH4+, NO3-, NO2- and urea and (ii) necessary modifications make desirable colorimetric procedures usable in a Na2SO4 extraction system.

A procedure for the colorimetric determinations of exchangeable NH4+, urea, NO3-, and NO2- in soil using a single soil extract is described. The soil sample is extracted with Na2SO4 containing phenylmercuric acetate for 30 min and then leached with four 25 ml portions of extractant and made to volume. The extract is analyzed for NH4+ by a modified Nessler reagent, urea by either diacetyl monoxime and thiosemicarbazide or p-dimethyl aminobenzaldehyde depending on concentration, NO3- by chromotropic acid and NO2- by 4-aminobenzenesulfonic acid and 1-aminonaphthalene hydrochloride. The procedure gave quantitative recovery of NH4+-N, urea-N, NO3- N, and NO2--N added simultaneously to five different soils.

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