Understanding how Diffuse Light Increases Yield in Tomato

Light is not uniformly distributed in greenhouses, but this can be improved if the light is diffuse. To determine the effect of diffuse light on crop growth and development, an experiment with tomato crop was conducted from December 2010 to November 2011 under commercial crop management. Three kinds of glass were used as greenhouse covering: standard glass (no diffuse light, 0% haze) and two types of diffuse glass which transformed an increasing fraction of the direct irradiation into diffuse irradiation (45% and 71% haze). As presented by Dueck et al. yield increased by 7.8% under 45% haze and by 9.4% under 71% haze, compared to the reference. During the experiment we performed measurements in order to understand these effects. Diffuse light penetrated deeper and more homogeneously into the canopy, which led to higher photosynthesis rates in the middle and bottom canopy layers. Furthermore, less photoinhibition was measured under diffuse light treatment when the outdoor irradiation was high. Under sunny conditions the temperature of upper leaves in the canopy was 3 to 5 °C lower in the greenhouses with diffuse glass compared to the control, while greenhouse air temperatures were comparable. The leaf anatomy, canopy structure , total nitrogen and chlorophyll contents of top, middle and bottom canopy layers were also studied in order to further explain the increased production under diffuse light. The results showed that diffuse glass on greenhouses is one way to improve the light use efficiency of greenhouse crops.