Premium
Reflectant Induced Modification of Soybean Canopy Radiation Balance. II. A Quantitative and Qualitative Analysis of Radiation Reflected from a Green Soybean Canopy 1
Author(s) -
Lemeur Raoul,
Rosenberg Norman J.
Publication year - 1975
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1975.00021962006700030006x
Subject(s) - canopy , leaf area index , photosynthetically active radiation , albedo (alchemy) , environmental science , radiometer , pyranometer , atmospheric sciences , radiant energy , radiation , evapotranspiration , shortwave radiation , irradiance , wavelength , spectroradiometer , agronomy , physics , optics , chemistry , botany , photosynthesis , reflectivity , art , ecology , biochemistry , performance art , biology , art history
This report is one of a series of papers describing reflectant‐induced modification of the canopy radiation balance. Water‐saving effects are expected since net radiation, which is the driving force for evapotranspiration, should be reduced by the reflectant treatment. The experiments were planned to establish reflection patterns over soybeans ( Glycine max. [L.] Merr. ‘Amsoy’) at Mead, Nebraska. This study was undertaken to determine reflection coefficients at various solar elevations and at two values of leaf area index (LAI = 2.5 and 5.5) of a normal, unreflectorized soybean canopy so as to develop a base line against which to evaluate the effectiveness of various factorial treatments of reflectant materials, times and amounts of application. Therefore, net radiation, incoming and reflected radiation (300 to 3,000 nm) and the corresponding energy spectra within the 380 to 1,550 nm wavelength band were measured using a net radiometer, an upright and inverted pyranometer and a spectroradiometer, respectively. The shortwave reflection coefficient, α s , as well as the coefficients for photosynthetically active radiation α(PAR) and near‐infrared radiation α(NIR) remained nearly constant throughout most of the day, but increased significantly when solar altitude was less than 35° The dependence of albedo on LAI was a function of wavelength. At medium to high solar elevations α(PAR) decreased with increasing LAI while α(NIR) increased sharply. At lower solar altitudes both α(PAR) and α(NIR) increased with increasing LAI. The radiant energy reflected from the soybean crop showed a strong spectral shift toward NIR wavelengths with the increase in leaf area.