Spectral Characteristics of Paper Mulch

In order to evaluate the use of paper as a mulch for plant production, this research investigated the optical characteristics of two recycled papers (Emboss and Eco, beige 120 g/m2, and dark brown 55 g/m2, respectively) and a silver-polyethylene film (Silver, containing aluminum powder). We measured transmittance and reflectance of these materials as mulches under light controlled and open field (Tottori Sand Dune) conditions. Reflectance was defined as a ratio of reflective radiance of the mulch surface to that of the reflection standard surface.Used as mulches, all three materials would inhibit weed growth as they prevented the penetration of light at 660 nm, which stimulates weed germination. Mean transmittance at 400-700 nm for all three was less than 1%. The reflectance of Emboss and Eco was low for ultraviolet (350-400 nm). but high for visible (400-700 nm) and near infrared rays (700-2, 500 nm). The opposite was found with Silver. The radiances of the three mulches on fair and cloudy days were compared. The radiance of the three mulches on the cloudy day were high for ultraviolet but low for visible and near infrared rays. The light scattering property of each material was measured hemispherically at 5 angles: 30°, 60°, 90°, 120° and 150°. Silver reflected light more strongly in the direction against the angle of the sun. In contrast, Emboss generally reflected more light than Eco in all directions, both had no significant differences among the directions. Because Emboss reflects photosynthetically active radiation (400-700nm) at a wider angle than Silver, it may be better for plant photosynthesis.