The initial results of a three-year trial being conducted by lighting supplier Signify and growing media producer Grodan at the Botany Research Centre in the Netherlands suggest that it is possible for tomato growers to maintain high levels of quality and production, even when heat inputs in the greenhouse are reduced.
The work, which was first announced last September, also involves partners including BASF Vegetable Seeds, Ridder, Normec Groen Agro-Control, and Wireless value. According to reports the trial has confirmed the benefits of the fully dimmable Philips LED lighting and Grodan stone wool growing media in Controlled Environment Agriculture (CEA), and produced some surprising insights related to humidity management and the nutrition balance in the root zone.
Two of the key findings are that with active dehumidification, growers can minimise the impact of the lower radiant heat input (lower pipe temperature, LED lights & increased screening hours) on the uptake of water and nutrients by the crop, and that adapting the nutrient recipe influences the growth habit of the crop and facilitates a lower energy input to the greenhouse.
The use of the air dehumidification unit contributes to a more uniform greenhouse climate, meaning there is minimal variation in temperature and humidity values which can be seen from the numerous wireless sensors installed. Thanks to the air movement, there is a very stable temperature profile, which makes it even easier to pursue a precision-growing strategy for uniform and consistent results.
“The dehumidification unit enables us to manipulate the ‘pull’ of transpiration rather than ‘push’ humidity into the greenhouse and this enables us to continually steer the crop towards optimum plant growth and development,” explained Andrew Lee, Knowledge Manager at Grodan. “Thanks to our stone wool growing media we can use the GroSens root zone sensor data to closely monitor the changes in the root zone water content % (WC%) and EC. This enables us to precisely control and adapt the irrigation strategy.”
The air-dehumidification unit has also helped maintain a high level of transpiration. “The norm for HPS lighting is usually 130 to 140ml of transpiration per mole of light, so at a 40% lower heat input we expected to see around 80 to 90ml. But in fact, based on the measured water content levels in the stone wool growing media, we are currently at around 100 to 110ml. This shows that if you actively manage the humidity, you can minimise the impact of the lower radiant heat input on the uptake of water and nutrients through the leaves,” he added. “Besides that, there was almost zero drain from planting in week 39 to first harvest in week 47. “Although that wasn’t our intention, it demonstrates that if you can control the water uptake, you can also precisely align the amount of water you give, helping you to further optimise water and nutrient input.”