Spectral Irradiance Available for Turfgrass Growth in Sun and Shade

The spectral quality of solar radiance affects plant growth and development. The purpose of this study was to assess the spectral quality of deciduous shade, coniferous shade, building shade, and full sun in a natural environment common to turfgrass growth throughout a day and throughout a growing season. A spectroradiometer was used to acquire solar spectra in these four environments. Acquisitions were made on an hourly basis from 0730 to 1930 h, biweekly, from vernal equinox to autumnal equinox at The Ohio Turfgrass Foundation Research and Educational Center and from 10 April to 1 July 1997 at The Ohio State University campus. Data were tested for variation in spectral quality between morning hours and afternoon hours in full sun and among full sun and deciduous, coniferous, and building shade. Results indicated that changes in spectral quality occurred between morning and afternoon periods in full sun, but total (red + blue) photosynthetically active irradiance was not affected. Measurements indicated that a deciduous tree and a conifer tree filtered significantly more high activity (red + blue) quanta than a building. Blue irradiance relative to total irradiance increased and red irradiance decreased with increasing shade density. Significant differences were detected between full sun, tree shade, and building shade for blue photoreceptor potential (blue photon flux/far‐red photon flux) and phytochrome potential (red photon flux/far‐red photon flux). Results indicated that relationships among blue, red, and far‐red irradiance that influence many plant responses were affected by both shade source and shade density.