Feature Story
TURFGRASS MANAGEMENT IN THE
SHADE By John Sorochan, Ph.D., Plant Sciences Department, University of Tennessee
W
hen it comes to managing turfgrass in shade, an understanding of the actual causes of shade is important. Shade is simply the lack of necessary
light for optimal turfgrass growth. Reduced light, or shade, results in reduced photosynthesis, in turn causing the induced turfgrass stress. A simple definition for photosynthesis is light energy plus carbon dioxide plus water yielding chemical energy (carbohydrates) plus oxygen plus water. Light (sunlight) is the ultimate source of most terrestrial life on earth. The sun provides light in abundance and does not appear to be a limiting factor for most turfgrass growth. However, changes in light, either quantity or quality, have dramatic effects on plants, thereby making it a limiting resource. The components of light include light quality and quantity. Light quality are the wavelengths of light (measured in nanometers, nm), and range from very short (cosmic or x-rays) to long (radio) waves lengths. Turfgrasses, like all plants, require
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visible light from 380 to 700 nm in order for photosynthesis to occur. This visible light spectrum (380 – 700 nm) is known as photosynthetically active radiation (PAR). Within PAR are the blue and red light wavelengths which are important components for turfgrass growth and development. Blue light (≈ 380 – 500 nm) is important for photosynthesis and is the stimulus for short sturdy growth. Conversely, red light (≈ 600 – 700 nm) is also important for photosynthesis and is the stimulus for turfgrass cell elongation. Green light typically is not important for photosynthesis and is reflected giving the turf its green color. Light quantity is the actual particles (photons) of light providing the energy necessary for photosynthesis to occur. Light quantity (energy) is the most important light component for photosynthesis to occur. The shorter the wavelength, the more energy provided; thus, blue light is more important for photosynthesis than red light.
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