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This article in AJ

  1. Vol. 68 No. 6, p. 848-852
     
    Received: Apr 23, 1975
    Published: Nov, 1976


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doi:10.2134/agronj1976.00021962006800060003x

Reflectant Induced Modification of Soybean Canopy Radiation Balance V. Longwave Radiation Balance1

  1. Maximo W. Baradas,
  2. Blaine L. Blad and
  3. Norman J. Rosenberg2

Abstract

Abstract

Potential water-savings and increased water use efficiency may result from reflectant-induced modification of the canopy radiation balance. This report is one of a series of papers describing reflectant treatment effects on the radiation balance. The objective of this study was to evaluate the effect of the reflectant treatment on the longwave balance over soybeans [Glycine max (L.) Merr.].

Average ratios of the flux densities of net longwave to global radiation on 3 and 9 August, were 0.251, 0.239, 0.257, and 0.241 over ‘Amsoy’ treated, Amsoy untreated, ‘Beeson’ treated, and Beeson untreated areas, respectively. Corresponding global radiation reflection coefficients were 0.207, 0.194, 0.235, and 0.211.

The flux density of outgoing longwave radiation was greater from the reflectorized crop than from the untreated crop. This was due both to an increase in the reflection of incoming longwave radiation and to an increase in the flux density of emitted radiation. The increased reflection of longwave radiation was due to a reduction in the longwave absorptivity; the increased emission was caused by the higher temperature of the treated canopy.

The reduction of net radiation over the treated areas resulted from the increased outgoing longwave radiation and from the increased reflection of global radiation. Both processes contributed about equally to the observed differences in the net radiative fluxes between treated and untreated canopies. A mechanism of radiation balance modification by reflectants is proposed to explain the observed changes in net radiation.

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