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This article in SSSAJ

  1. Vol. 38 No. 2, p. 273-277
    Received: Aug 28, 1973
    Accepted: Nov 27, 1973

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A Kinetic Study of Ammonium and Nitrite Oxidation in a Soil Field Plot1

  1. M. S. Ardakani,
  2. R. K. Schulz and
  3. A. D. McLaren2



Disappearance of NH4+ from percolating solution in a 40 m2 plot is at first attributable to both oxidation and to adsorption by the soil. Once a steady state was established and exchangeable NH4+ was equilibrated with NH4+ in soil solution, oxidation alone accounted for disappearance of NH4+ — N in the top 2.5 cm of the soil. Concentration profiles of NO2- and NO3- are described by a modified Michaelis-Menten equation. Rate constants for oxidation of NO2- → NO3- and NH4+ → NO2- are 0.6 × 10-3 and 2.5 × 10-3 ppm/hour·cm3 per bacterium, respectively. These rates are in good agreement with the values found under controlled laboratory conditions.

Growth and distribution in soil of Nitrobacter and Nitrosomonas sp. were followed by weekly estimates of their numbers at different depths. The former reached a maximum population of about 106/cm3 of soil but declined to a stable density of about 105 organisms/cm3; the latter approached a steady level of about 104 organisms/cm3. Both organisms showed higher densities near the soil surface where the concentrations of substrates were always highest.

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