Effects of Reflectors, Black Boards, or Shades Applied at Different Stages of Plant Development on Yield of Soybeans1

Abstract

Our objective was to determine the effects of a 2‐week period of light enrichment or reduction at various stages of plant development on the number of pods and on seed yield of soybeans (Glyclne max (L.) Merr.). Soybeans were field‐grown at uniform populations on Wooster silt loam soil (Typic fragiudalf, mixed mesic). In 1973 and 1974 aluminum foil reflectors were positioned at a 45° angle to the ground on the north side of east‐west rows for a duration of 2 weeks. Reflector treatments, which were established weekly, increased the amount of photosynthetically active radiation received by the plants 57%.In 1973 plants with light enrichment during late flowering and early pod formation, the period of greatest response, had 48% more pods (frults)/plant at maturity than controls. Stem plus fruit weight and total seed weight were increased 50 and 57%, respectively, over controls at maturity.In 1974, black boards (non‐reflective surfaces), positioned in the same manner as the reflectors, and shades that gave a light reduction of 63%, were included as treatments for 2‐week periods. Reflector and black board treatments imposed at late flowering or early pod formation caused a 31 and 28% increase, respectively, over controls in the number of pods/plant at maturity. Seed yield from plants treated at the same period with reflectors and black boards was 40 and 27%, respectively, greater than controls. The number of pods and seed yield for shaded plants was reduced as much as 16 and 29%, respectively, below that of the controls. All plants aborted a large percentage of pods (27 to 34%) from 12 August to maturity.