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This article in AJ

  1. Vol. 77 No. 6, p. 884-889
     
    Received: Nov 23, 1984


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doi:10.2134/agronj1985.00021962007700060013x

Estimating Ammonia Flux: A Comparison Between the Integrated Horizontal Flux Method and Theoretical Solutions of the Diffusion Profile1

  1. K. J. McInnes,
  2. D. E. Kissel and
  3. E. T. Kanemasu2

Abstract

Abstract

Estimating the loss of N fertilizer as ammonia from the ground to the atmosphere via the integrated horizontal flux method (IHF) generally requires measurement of the mean atmospheric ammonia density and the mean wind speed at five or more heights. Using acid traps as a means of measuring ammonia density at that many heights over long periods of time proves laborious, and a way of reducing the number of heights is desirable. This paper presents an application of an analytical solution of the diffusion equation for local advection to the estimation of the loss of ammonia from a small circular (20 m radius) plot fertilized with 200 kg N/ha urea-ammonium nitrate solution. Predicted ammonia density profile shapes agree well with those measured at the center of the plot. The estimated fluxes obtained from the “theoretical profile shape” solution (TPSP) show much less variation than those from a recently proposed single-height method (TPSW), when compared with estimates from the IHF method using mean wind speed and mean ammonia density at five heights. The ratios of FTPSP/FIHF were found to be generally > 1 under unstable atmospheric conditions and < 1 under stable conditions. The advantages of TPSP over TPSW are that samples may be taken where the error to magnitude of measurement ratio is smaller and the solution is simple to calculate for any size plot, provided an estimate of atmospheric stability may be made.

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