Soybean Canopy Structure and Some Radiant Energy Relations¹

Abstract

Abstract Measurements were made of canopy outline, leaf area index and the radiation environment of a soybean row crop at several stages of growth. The major change with time in canopy geometry occurred in the uppermost hemicylinder of leaves which increased in height and lateral spread. The proportion of energy reflected and reradiated from the top of the canopy increased during the season and this may be related to increases in both leaf area index and lateral spread of the crop. A nonlinear relationship between the incoming radiation and the energy received at a plane within the crop indicated that changes in leaf inclination during periods of high insolation gave a more open canopy. Measurements of energy in the 310‐ to 2750‐nm waveband showed that from 65 to 85% of the radiation received at a plane in the crop came from the upper hemisphere and the remainder was reflected to the under surface. Extinction coefficients, calculated for solar radiation, showed large changes with height in the canopy, indicating that the assumptions made in applying the Bouguer‐Lambert law to energy relations in a soybean canopy are not valid. Any model of the radiation relations of row crop canopies must account for energy changes in both the vertical and lateral directions.