Agricultural Research Service studies have shed more light on how the color of plastic mulch can affect food plants.
Past ARS work showed that red mulch produced larger tomatoes and sweeter-smelling, better-tasting strawberries. More recent work with cotton, carrots and basil focused on how color can affect the roots, stems, leaves and seeds, as well as the fruits, of many other food and crop plants.
The ARS studies were led by plant physiologist Michael J. Kasperbauer, who recently retired from ARS' Coastal Plains Soil, Water and Plant Research Center at Florence, S.C. According to Kasperbauer, colored-mulch technology's controlling factor is not the colors themselves, but how the colors change the amount of blue light and the ratio of far-red (FR) to red light that plants receive.
Research on cotton showed that cotton fibers grew longer in bolls exposed to increased FR-to-red light ratios. Another study, on carrots, revealed that concentrations of nutrients and compounds such as beta carotene and vitamin C in the roots of food crops could be modified by reflecting the right waves of color onto the plants' leaves.
In studies with basil, the amounts of blue, red and FR light reflected onto developing leaves affected their size, aroma and concentration of soluble phenolics. The phenolics are natural compounds, including tannins and pigments that can induce color, some flavors and odors, and antioxidant activity.
Basil leaves developing above red mulches had greater area, succulence and fresh weight than those developing above black mulch. When grown above yellow and green mulches, basil leaves developed significantly higher concentrations of aroma compounds and phenolics than did those of plants grown above white and blue mulches.
Read more about colored mulch research in the September issue of Agricultural Research magazine, available online at: http://www.ars.usda.gov/is/AR/archive/sep03/mulch0903.htm