Effect of diffuse glass on climate and plant environment: First results from an experiment on roses

High energy use in rose cultivation at higher latitudes is caused by the need for artificial light to supplement scarce sun radiation. On the other hand, since too high radiation levels are known to reduce flower quality, shading is widely applied during spring and summer, either through movable screens or seasonal whitewash. In both cases damage to the crop is avoided at the cost of reducing potential assimilation by reduction of (PAR) light. Recent research on cucumber has shown that diffusing cover materials have the potential of improving the uniformity of vertical light distribution in a crop, therefore decreasing the energy load on the uppermost crop layer to the advantage of underlying crop layers. Light diffusion, however, usually implies a loss of overall transmission. This drawback can be avoided by antireflection coatings, so that most recently diffusive glass covers have become available with the same transmissivity of standard glass. The application of such a cover on roses could decrease the need for shading so that a desired radiation sum could be achieved with less need for artificial light. Such an experiment is in progress on a crop of roses (cv. Red Naomi) at the research station of Wageningen UR Greenhouse Horticulture in Bleiswijk, NL, in two compartments. One is covered with diffuse glass with anti-reflection coating with a light transmission of 93% perpendicular and 83% hemispherical and haze factor of 72%. The reference compartment is covered with standard glass. This paper describes the effect of a diffusing cover on the greenhouse climate (air- and plant-temperature, humidity and ventilation requirement) and water balance compared to a greenhouse covered with standard glass. It’s shown that the effect on greenhouse climate is limited but flower temperature is reduced in the diffuse compartment which has effect on flower quality. It seems therefore that the material has potential for reducing leaf burning and if the use of shade screens or whitewash can be reduced there is a potential increase of yield with the same energy inpu