Jan Voogt is not only a researcher and consultant - he is also a proponent of Next Generation Growing (HNT). This new way of growing was developed some years ago and focuses on optimizing crop production without unnecessary consumption of energy and water. Therefore they adapt new attitudes to basic environmental conditions such as temperature and humidity. "If you look at the greenhouse climate and the functioning of the plant from a physics point of view you will see that everything lines up. That's the beauty of Next Generation Growing. Everything becomes a lot easier." Voogt sees excellent opportunities for growers to manage with less CO2. In the Netherlands, this recently became an important subject due to a lack of CO2-supply.
Less ventilation
Less use of CO2 starts with losing less CO2. Voogt: "One of the ideas of HNT is limiting loss by ventilating less." With classical cultivation the temperature of the greenhouse is lowered by airing too often. "The result is that CO2 is blown out of the greenhouse." Another disadvantage of ventilating is lower humidity, which causes the stomata to close. "While plants grow better with higher humidity and higher temperatures. These cause the stomata to remain open and the plant to better absorb CO2."
So according to Voogt too much ventilation has two disadvantages: too much CO2 loss and poor CO2 absorption. "We turn that around completely: you keep moisture and CO2 in the greenhouse to ensure a better growing plant."
Energy content
There is another advantage to this cultivation style. It may seem more difficult to keep the climate under control with less ventilation, but according to Voogt this is quite the opposite. Air can contain more energy with high humidity than at low humidity and is therefore easier to control. "At high humidity you need to exchange less m³ of air to get the same effect on your temperature."
Web lecture (in Dutch) of Energiek2020 on enthalpy, the energy content of greenhouse air. What is the difference between tangible and latent energy and how can you keep more CO2 in the greenhouse by aiming at a high RH in sunny weather? More web lectures can be found on Kas als Energiebron.
Practical use
There are several ways to use CO2 more effectively in cultivation. "Another part of CO2 saving is simply to apply CO2 when it is beneficial for the plant: in combination with solar radiation. When there isn’t much radiation, you don’t have to give much. Less light is less photosynthesis so less CO2. This is another way you can avoid waste." Research shows that this makes it possible to grow with half the usual amount of CO2 per hectare.
Lazy plants
The last of the three points is one that will not help growers who always make ample use of CO2 and won’t have enough now - but it isn’t less relevant for horticulture as a whole. Plants can become 'lazy' due to an excess of CO2. "If they always have plenty of CO2, photosynthesis becomes less efficient. The chlorophyll gains less from the available CO2." Teaching the plant to deal with less CO2 early on can lead to a more efficient production of assimilates by certain crops. "Something to keep in mind: if you always give a lot, you need to continue to do so with certain breeds."
Voogt’s tips don’t suddenly make it possible to work without CO2. "The CO2 supply stop is extremely unfortunate now that the plants are at the peak of their CO2 demand. But it is certainly possible to use the scarce CO2 more effectively."