SOIL LIGHT PENETRATION AND DORMANCY OF JIMSONWEED (DATURA-STRAMONIUM)SEEDS

Trials were carried out to determine the degree of light transmittance through soil and its role in photo-induced germination of buried weed seeds. Transmittance was found to be strongly dependent on soil type and decreased with decreasing particle size and with an increase in da rker components, In each soil examined, light penetration fell below 0 .01% at a depth of no more than 4 mm. It was also noted that with incr easing soil depth, light permeability was proportional to wavelength, leading to progressive decline in the red-far red ratio. Low light pen etration played a crucial role in germination of jimsonweed seeds, whi ch had became light-sensitive after prolonged burial. Although this ef fect is a function of soil type, it may represent an important ecologi cal factor influencing seed emergence in the first few mm of upper soi l layers.