Effects of light-diffusing plastic film on lettuce production and quality attributes

In general, plants grown under diffuse light yield higher biomass than those grown under direct light as a result of a more uniform distribution of the light across the plant canopy. We compared the effects of a light-diffusing plastic film and a clear plastic film on growth of Batavia lettuce (Lactuca sativa L.) in two greenhouses during five growth periods. Lettuce grown under the light-diffusing film were smaller (up to 36%) than control plants grown under the clear film, due to the fewer leaves per plant (up to 22%) and lower mean values of individual leaf area (up to 29%). The photosynthetically active radiations use efficiency was sometimes lower (up to 23%) in lettuces grown under the light-diffusing film. The pigment contents tended to be lower in plants grown under the light-diffusing plastic. The total macroelement contents of the lettuces grown under the light-diffusing plastic were up to 10% higher than in the lettuces grown under clear plastic, mainly as a result of higher leaf K contents (up to 19% higher). In addition, use of the light-diffusing plastic tended to increase leaf nitrate contents (by up to 23%). The leaf solid soluble content and acidity values were higher in the lettuces grown under the light-diffusing plastic, while leaf pH values were lower than in the control plants. The findings showed that the light-diffusing plastic was detrimental to production of compact heads of lettuce, and to some quality parameters such as nitrate and pigment contents. Nevertheless, open-leaf cultivars would likely show a different response to the diffuse light