Interception of light by the foliage of pure and mixed stands of pasture plants

Abstract

Relationships between light interception and leaf area in the regrowth of pure stands of short-rota,tion ryegrass (Lolium perenne L. x L. multiflorum Lam.), perennial ryegrass (L. perenne), timothy (Phleum pratense L.), white clover (Trifolium repens L.), and a mixed stand of short-rotation ryegrass and white clover, were determined for cloudless conditions. The relationship between light penetration and elevation of the sun was also examined. The leaf area indices at which 95 per cent. of the incident light was intercepted about midday in midsummer mere as follows: short-rotation ryegrass, 7.1 ; perennial ryegrass, 7.1; timothy, 6.5; white clover, 3.5; and the mixed stand, 4.5. The percentage of incident light penetrating through the foliage on cloudless damp in summer changed considerably with time of day. The highest values were recorded at local noon and the lowest 2-3 hours after sunrise or before sunset. These results are attributed to the angle of incidence of the light, and suggest marked seasonal differences in the leaf area required to intercept 95 per cent. of the light. It is suggested that midwinter values are approximately one-half of mid-summer values. The results are discussed in relation to the light-intercepting capacities of the leaves of the different species, plant competition, and pasture management.