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This article in AJ

  1. Vol. 104 No. 2, p. 225-240
     
    Received: Mar 18, 2011


    * Corresponding author(s): paul.colaizzi@ars.usda.gov
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doi:10.2134/agronj2011.0082

Radiation Model for Row Crops: I. Geometric View Factors and Parameter Optimization

  1. P. D. Colaizzi *a,
  2. S. R. Evetta,
  3. T. A. Howella,
  4. F. Lib,
  5. W. P. Kustasc and
  6. M. C. Andersonc
  1. a USDA-ARS, Conservation and Production Research Lab., P.O. Drawer 10, Bushland, TX 79012-0010
    b Geoscience Australia, National Earth Observation Group, Cnr Jerrabomberra Av & Hindmarsh Dr, Symonston, ACT 2609, GPO Box 378, Canberra ACT 2601, Australia
    c Anderson, USDA-ARS, Hydrology and Remote Sensing Research Lab., Building 007, BARC-West, Beltsville MD 20705-2350. The USDA prohibits discrimination in all its programs and activities. The USDA is an equal opportunity provider and employer. The mention of trade names of commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA

Abstract

Row crops with partial cover result in different radiation partitioning to the soil and canopy compared with full cover; however, methods to account for partial cover have not been adequately investigated. The objectives of this study were to: (i) develop geometric view factors to account for the spatial distribution of row crop vegetation; (ii) combine view factors with a widely used vegetation radiation balance model; and (iii) optimize three parameters required by the model that describe leaf angle, visible leaf absorption, and near-infrared leaf absorption. Measurements of transmitted and reflected shortwave irradiance for corn (Zea mays L.), grain sorghum [Sorghum bicolor (L.) Moench], and cotton (Gossypium hirsutum L.) were used to optimize parameters and evaluate the model. View factors were derived by modeling the crop rows as elliptical hedgerows. The optimized ellipsoid leaf angle parameter, visible leaf absorption, and near-infrared leaf absorption were 1.0, 0.85, and 0.20 for corn; 1.5, 0.82, and 0.20 for grain sorghum; and 3.0, 0.83, and 0.14 for cotton, respectively. Visible leaf absorption was similar for all crops. Near-infrared leaf absorption was the same for corn and grain sorghum but less for cotton. The only parameter that changed for each crop species was leaf angle. The optimized parameters for corn and grain sorghum were within the range of values recommended in previous studies, and the leaf angle parameter for cotton agreed with a previous study of cotton leaf angles. All parameters were distinctly identifiable, and no parameter correlation was observed.

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