OVER-WINTER CHANGES IN RADIANT ENERGY-EXCHANGE OF A CORN RESIDUE-COVERED SURFACE

Crop residues on the soil surface absorb solar radiation and have refl ectivity properties that may differ significantly from the underlying soil. The objective of this study was to measure the temporal variatio n in solar radiation reflectivity and transmissivity of a corn (Zea ma ys L.) residue layer under field conditions. Incident and reflected so lar and visible radiation were measured in a field with standing corn stubble and corn residue prostrate on the soil surface. Transmitted so lar and visible radiation were measured with line sensors placed benea th the prostrate residue, Measurements were made during snow-free peri ods from October 1994 to April 1995. Mean reflectivity decreased from 0.20 +/- 0.02, 0.12 +/- 0.02, and 0.27 +/- 0.03 for the solar, visible , and near-infrared wavebands during the fall, to 0.17 +/- 0.01, 0.11 +/- 0.01, and 0.22 +/- 0.02 during the spring measurement period, resp ectively. Transmissivity of solar and visible radiation through the co rn residue layers was directly proportional to residue area index. Ext inction coefficients for solar and visible radiation ranged from 0.79 to 0.96 and were higher in the fall for both wavebands. Diurnal patter ns of reflectivity and transmissivity showed a sensitivity to the prop ortion of beam vs. diffuse radiation and wetness of the residue. (C) 1 997 Elsevier Science B.V.