title: Light Penetration and Light-induced Seed Germination in Soil.
abstract: Light penetration through a Drummer silty clay loam and a Broomfield sand was measured spectrophotometrically and biologically. The spectrophotometric measurements showed that less than 1% of the incident light penetrated 2.2 millimeters at any wavelength between 350 and 780 nanometers for ped sizes up to 1 millimeter. Biological measurements with light-sensitive lettuce (Lactuca sativa) seeds in soil showed that an exposure to light equivalent to about 1 sunny day induced some germination of seeds which were 2 millimeters below the surface, but did not affect seeds 6 millimeters below the surface.
authors: United States Department of Agriculture, Agricultural Research Service, Agronomy Department, University of Illinois, Urbana-Champaign, Illinois 61801.
authors: J T
authors: JT
authors: Woolley
authors: E W
authors: EW
authors: Stoller