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Agronomy Journal Abstract -

Reflectance Differences Between Target and Torch Rape Cultivars1


This article in AJ

  1. Vol. 73 No. 3, p. 556-559
    Received: Sept 22, 1980

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  1. H. W. Gausman and
  2. R. W. Leamer2



To characterize and explain leaf and plant reflectance differences between Target (Brassica napus L.) and Torch (Brassica campestris L.) rape cultivars, laboratory spectrophotometric reflectance measurements were made on leaves of the same age, collected from different nodes, and on leaves of different ages, collected from the same node, for both small (five leaves) and large (nine leaves) Target and Torch plants. Spectroradiometric reflectance measurements were made on Target and Torch plants (four and five leaves, respectively) that were growing in 0.09 m2 soil-containing flats. Torch's spectrophotometric single leaf reflectance was consistently lower than Target's at the 650-nm chlorophyll absorption band because Torch's chlorophyll concentration was larger than Target's, which caused more red light absorptance. Spectroradiometric measurements indicated that: (1) wet soil strongly absorbed visible light (500 to 700 nm) so that Target's soil-containing flat with 60% plant cover had less reflectance than Torch's soil-containing flat with 75% plant cover, (2) Torch (most foliage) had higher near-infrared (750 to 1,350 nm) reflectance than Target (least foliage), and (3) the 2,200-nm wavelength is a candidate band to distinguish Target from Torch. The difference in chlorophyll concentrations between Target and Torch, compared with leaf structural differences, is apparently the most important factor that would affect the infrared color film's tonal response to vegetation in the photographic sensitive region (500 to 900 nm).

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