Dutch growers who are directly involved in research into Next Generation Growing soon discover that they can apply small parts of it to their own nurseries. At first sweet pepper grower Danny van der Spek was sceptical about the high energy target set in the research, but he is gradually adopting some aspects himself. However, it is difficult to translate the results from relatively small research sections into real life situations.
Every Monday, Danny van der Spek from Bergschenhoek visits the Next Generation Growing sweet pepper trials being run at the Delphy Improvement Centre (IC) and Wageningen University & Research in Bleiswijk. He discusses the condition of the crop and the climate settings with his colleagues Kees Vijverberg, Maikel van der Berg and Ard Ammerlaan and the other advisors on the research supervisory committee there. “It is extremely interesting and informative,” he explains. “It doesn’t take up much time but it does give you a good picture over an extended period of time. What’s more, you can adopt some of the positive results in your own climate control.”
Van der Spek has 9 ha of orange peppers split into two sections. His Venlo greenhouses are equipped with a double energy screen. His situation is quite similar to the one at the IC. There are fewer similarities with the parallel trial at Wageningen University & Research as the VenlowEnergy greenhouse has a double glazed roof. “That’s not a situation you will find very often in practice, simply because it’s too expensive,” he comments. But the comparison between double and single glazing is nonetheless interesting.
The pepper selected for both trials was the heat-loving red standard variety Maranello. The 1,000 m² section at the IC has two transparent energy screens and is equipped with horizontal and vertical fans. Heating is kept to a minimum in this section.
Whereas energy consumption at commercial nurseries is usually about 30 m³/m², the trial participants want to demonstrate that energy consumption of 20 m³/m² is achievable. That is a saving of more than 30%. This target was achieved at the end of 2016, with energy consumption as much as 2 m³ less than projected. Maximum use of the energy screens and omission of the minimum pipe therefore had a massive impact.
The sweet pepper grower describes himself as a “pretty heavy stoker”. He sees the minimum pipe as a way of keeping the crop active. That’s how he learnt it and that’s how he has always done it in practice. “I actually want to get away from the minimum pipe,” he explains. So following these trials and comparing them with a down-to-earth vision of professional practice appealed to him. The project, which is based on the principles of NGG, offers opportunities to approach climate control from a different angle.
When he heard about the high energy target, his ears pricked up. “I thought the target was extremely high and didn’t expect it to be met without loss of quality or production. The fact that it was, is very special,” he says.
Energy screens dominate
In the trials, the use of the energy screens was the dominating factor. The top screen opens when radiation reaches 100 W/m². The second screen follows when the temperature above the screen differs from the desired heating temperature by four degrees. This small difference should prevent a cold dump.
There were times in the spring of 2016 when the bottom screen was still closed with radiation at 300-500 W/m². The intensive use of the screens led to a 14% light loss between the start of cultivation and early April. That was difficult for the growers to get used to as they prefer to allow in as much light as possible.
Van der Spek: “The screens were closed a lot. They are even used at night in the summer to protect against outgoing radiation. The windows are left closed as long as possible so that the greenhouse is warmed up by the sun, not the pipe. With a net radiation meter at the top of the greenhouse, we can monitor that closely. You would expect the crop to suffer but it didn’t seem to. I have always been very impressed with the condition of the crop. Although you do have to take the small surface area of the trial into account. In a large greenhouse it could be harder to get rid of moisture because there is proportionately less wall surface area.”
Higher 24-hour temperature
It soon became apparent that production and fruit quality were keeping up well with commercial nursery standards. Losses were low and no internal rot was observed. The crop in the trial with double glazing was slightly stronger and showed more growth. In fact, blooms were slightly ahead of those in commercial nurseries. The 24-hour temperature was also a little higher.
That brings the grower back to the situation at his own nursery. He has gradually started applying some of the principles from the trials there. “For me personally, the greatest benefit comes from screening more and from the slightly higher 24-hour temperature. The more light you can let in, the more the plant can do with the sugars it creates,” he explains. “We still have to find out how high the 24-hour temperature needs to be for that.”
Translating into practice
The intensive use of screens in the trial resulted in significant energy savings, particularly in April. The fans – first the horizontal ones and later the vertical ones – ensured an even distribution of temperature and humidity. This has taught Van der Spek that January and February are not good months for saving energy, whereas March and April are. From then on and throughout the summer, he uses very little gas.
Nonetheless, it is difficult to translate the results of the trials straight into practice. “We growers have to leave the CHP running, you see, even when we need less heat,” he explains. “I myself have an OCAP connection which delivers us CO2 from industrial plants around Rotterdam, but not every nursery has that. In these situations the CO2 supply is the bottleneck.”
The research into NGG and the different approach to climate control whets the appetite for more. Van der Spek: “We growers are actually keen to continue with the research as there are still a lot of unanswered questions. I was very sceptical to begin with, given the results of previous studies. I will be looking at things differently after this season.”
Text and images: Pieternel van Velden