Saint-Gobain Cultilene and Hortilux work closely together in Plant Empowerment
Keeping the plant in optimal balance in terms of water, energy and assimilates – that’s what Plant Empowerment is all about. To achieve this balance, factors such as irrigation and light input must be optimally aligned. Saint-Gobain Cultilene and Hortilux – both partners of the Plant Empowerment growing philosophy – therefore work intensively together and advocate a systematic approach.
Plant Empowerment is all about creating an optimal balance in terms of water, energy and assimilates. If all these factors are properly managed and the balances are in the right proportions, the plant is completely in balance. “This can achieve a great result” says Remy Maat, Manager Application at Cultilene. “It can produce a healthier, more resilient crop, better quality and higher yields, for example. It also allows you to save on water, fertilizers, energy and crop protection products. The areas in which the most gains can be made differ from one grower to the next and depend on where a nursery currently stands.”
Closely connected
Cultilene has been a partner in Plant Empowerment (GPE) ever since its inception. All the partners have their own focal areas. Cultilene focuses mainly on irrigation. As a supplier of grow light solutions, Hortilux’s main specialist field is light. Cooperation between the two partners is clearly needed, stresses Hans de Vries, Consultant Grow Light Performance at Hortilux. “Light and irrigation are factors that influence each other strongly and are closely connected. After all, light is the driving force behind photosynthesis and therefore the production process. But if water and nutrients are in short supply, photosynthesis stagnates and the plant can’t make use of the available light. To achieve a good plant balance, light input and irrigation must be optimally aligned.” Maat agrees, pointing out that both the amount and type of light in a greenhouse impact on irrigation. “The more light and solar radiation there is, the higher the temperature will be in the greenhouse and the more water the plant will need to keep cool. The type of light source – sunlight, HPS or LED – also plays an important role. HPS lamps give off much more heat than LEDs, which means that they also impact differently on the plant and transpiration. You have to take that into account when providing water and nutrients.” As a rule of thumb, the higher the light input and the temperature are, the more water will be needed. “At the same time, we lower the EC as the temperature rises. At a higher temperature, the plant needs more water but the amount of nutrients it needs remains constant. If the EC is too high, it becomes harder for the plant to absorb water, which can potentially have an adverse effect on plant growth.” Maat also points out that the amount of water and EC are always adjusted based on the amount of available light in the greenhouse and not the other way round. “This makes sense, actually: grow light is a fixed item that isn’t easy to change, whereas water can always be given in the right quantity.”
Uniform watering in winter months
The two GPE consultants point out that winter is a special period when it comes to the relationship between light and irrigation. At this time of year, light input from outside is relatively low, and growers usually use supplementary lighting for the same number of hours every day. “Light is therefore a pretty constant factor. That also means that you have to approach irrigation differently: it can follow a relatively uniform rhythm,” Maat says. “A 24-hour period is usually divided into three periods. It starts with a dark period, between 6 pm and midnight. No water is given then. At midnight, the lights go on. We start watering two hours after switching on the lights at the earliest. While the lights are on at night, we water two or three times at most, up until about two hours before sunrise. Then the day starts, which runs through until 6 pm. Our first daytime irrigation is two hours after sunrise, after which we switch to a normal daily rhythm.” However, De Vries points out that the amount of available light in the greenhouse fluctuates more in spring and autumn due to the bigger differences in outdoor conditions and in the amount of sunlight. “That also requires more adjustments to the irrigation and EC supply. At this time of year, your irrigation can generally follow a less consistent rhythm than in the winter months.”
Systematic approach
In summary, aligning the irrigation to the amount of available light in the greenhouse is no easy task. “In fact, it’s quite a challenge. Especially now that grow light is gaining ground and more and more different types of grow light are being used,” Maat says. “Within GPE, we are therefore working on a protocol with guidelines for irrigating while grow light is being used. This should give growers tips on how to handle this properly.”
According to Maat and De Vries, a systematic approach is very important. Their advice for growers is to work out on paper in advance how much light – based on the plant load – you need in your greenhouse every week and how the lighting is geared towards this. “You can then also roughly align your watering to this,” De Vries says. “If you don’t make a plan, you will have to make more ad hoc adjustments and you will be in a constant cycle of catching up. For example, many tomato growers start with an extra stem around the darkest day. This also means that in the following weeks, more light will gradually be needed and irrigation will have to be stepped up. It is a good idea to plan the timing of these actions carefully: last-minute adjustments are very tricky to make.” As Maat points out, major corrections in the cropping strategy are best avoided anyway. “Reacting in extremes is never a good thing: it impacts negatively on the plant balance and therefore ultimately on yields and quality. A plant must be able to grow uniformly and consistently. In other words, anticipating instead of reacting is what it’s all about.”
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