"Less stress in ficus with diffuse coating"
The company’s major crop is ficus of various species in 17 and 21 cm pots. The other main crops are Curcuma and Hibiscus. For the last three years the company has used the diffuse coating ReduFuse, explains company manager, Mart van Holsteijn. “Before that, we only used the two shade screens. But when we started to work with the program ‘growWatch’, we noticed that the plants became quite stressed,” he says. GrowWatch uses sensors placed on and around the plant to measure humidity, CO2 level, light intensity (PAR-light) and the stress level of the plant.
The trend in potted plants is to increase the light level. Kwekerij Zwethlande has moved up from a maximum of 10-12 mol/m² to 15 mol/m². That is only possible if the humidity remains at the right level and light peaks are avoided. A diffuse coating is just what is needed. The light penetrates deeper into the crop so that more net photosynthesis takes place. At the same time, the top of the plant is spared and no light spots with a high light intensity occur. “Since we’ve been using ReduFuse, we’ve seen faster growth. The colour is better and the leaf initiation is faster. Also, the leaves become bigger. Curcuma and Hibiscus have a deeper flower colour and in general quality is better. In addition the biological approach to pest control is better because the natural predators suffer less from direct radiation,” says Van Holsteijn.
This season for the first time the greenhouse has been coated with ReduFuse IR, which not only makes the light diffuse but also inhibits heat radiation (infrared) so the crop and the greenhouse warm up less quickly. The company manager expects he can use the screens and open the vents later so there will be less loss of CO2. Both more light and more CO2 enable even better growth and quality. He admits that the switch to the new coating requires a different screening strategy. “Previously we applied ReduFuse to the roof in week 6. Because ReduFuse IR does take away some more light, we have decided to apply it in week 13. This requires more use of the screen cloth in March to reduce the strong radiation after the winter. You do get slightly higher light losses in the beginning, but I expect, on the basis of experience by colleagues, that it will be compensated for later.” He has changed the screen settings so that they close at 600-700 Watt/m² instead of 400 Watt/m² (measured outside). Depending on the experience encountered later in the season this might be adjusted further. “In the past we sometimes left the ReduFuse on the roof during the winter. That won’t happen with ReduFuse IR. We’ll remove it at the end of September or early October otherwise we’ll lose too much light in the autumn,” he says.
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