Both energy savings and increased production are feasible.
The 2SaveEnergy greenhouse focussed in the past year on the high-wire cultivation of cucumbers.
During two cultivation rounds, Wageningen University & Research investigated the possibility of growing a crop that could intercept and use light optimally (even in winter). This test formed part of preliminary research for future tests in the winter light greenhouse, a greenhouse design that allows in 10% more light in the winter.
The cultivation in the innovative greenhouse went well in the opinion of the crop researchers Jan Janse and Frank Kempkes. At the end of November, the crop was cleared out, and the total yield was estimated at 110 kg and 260 cucumbers. “And that with a minimal input of energy,” confirmed Janse. “Over the entire year we used about 17.5 cubic metres of gas. This puts us again well under the average found in practice.” The innovative greenhouse thus proves its worth again. The greenhouse concept makes it clear that Next Generation Cultivation can yield even more energy savings, while upholding production and quality.
This highly insulated greenhouse on the grounds of the Innovation and Demonstration Centre (IDC) Energy in Bleiswijk is a greenhouse with clear glass and a permanently present, high light-transmitting, diffuse foil layer parallel to the glass. The greenhouse is fitted with a dehumidifier system using outdoor air via hoses under the gutter. Researchers planted the cucumber variety Hi-Jack in the greenhouse on December 29. The crop control was carried out by varying the aisle width, plant spacing and fruit thinning. The optimum was determined in advance with a model. During two cultivation rounds, the team intensively monitored the interception of light, cultivation (crop, production and quality) and energy consumption.
Varying aisle widths
Janse said, “We chose to start planting at a density of 1.67 plants/m2, with three different aisle widths: 1.4, 1.6 and 1.8 m. This research was intended to test which aisle width led to the best crop production – used the light the best – while still being feasible. You have to be able to drive with the high-wire cart through the cucumbers without damaging the plants too much. Every treatment consisted of three ‘carrousels’ (cultivation gutters). For each treatment, the periodical crop observations were carried out on one carrousel.”
Kempkes documented the process by taking photos from a set position above the crop every week at a set moment. With an image-processing programme, the researchers could follow the development of the crop and the projected leaf surface area. This is an indication of the light interception. Kempkes added, “If you still see a lot of the floor or cultivation gutter on the photos, for example, then the light interception is not optimal.”
45% lower gas consumption
At the end of January, the plants were doubled by topping off. “At a certain moment there was a strongly generative growth with small leaves, but which yielded a great many cucumbers. During six weeks (weeks 15 – 20) the crop even produced 10 cucumbers weekly, or 4.5 kg/m2. Apparently, the plants coped very efficiently with their assimilates.” According to Janse, even the two growers from the supervisory committee were becoming envious of the crop. “The plants were sturdy, and the production was high, better than in the practice. We are still conducting research into the concrete causes of this phenomenon. It could partly be due to the good care taken of the crop. A striking aspect was for example the temperature achieved: it was on average 1 degree higher than at the growers’. The cucumbers benefited relatively quickly as a result. Averaged over the entire period, the development time was about 14 days at an average greenhouse temperature of 21.4°C. The aisle widths of 1.4 and 1.8 had the highest production. The consumption of gas and pure CO2 was 12.7 m3 and 4.5 kg per m2, respectively. This translates to a savings in gas consumption of 45% in comparison with the practice.”
Later second planting
In mid-July the team prepared a new crop. This time the variety was Hi-Power with a plant density of 2.25 plants/m2, and with the same three aisle widths. In the lightest period there was thus a gap of three weeks between the end of the first crop and the start of the second. “We deliberately planted a bit later because we wanted to test the crop in the darker period as far as possible. It was after all preliminary research for the Winter light greenhouse. At the end of October we harvested from this second round 100 cucumbers with an average fruit weight of 420 g. The crop was successfully rounded off, and we realised an excellent total production of high-quality cucumbers.” In this case as well, the aisle widths of 1.4 and 1.8 had the best results. The design was thus a success. With a relatively limited quantity of leaves or small leaves, characteristic of this variety, an excellent production can be realised. The crop apparently intercepted sufficient light, thanks to the east-west aisle orientation and a precise, even distribution of the crop wires, and a large proportion of the assimilates went to the fruits. Abortion rarely occurred. Smaller leaves also mean less transpiration, which saves energy in cold periods.
Winter light greenhouse
The research into an efficient winter light crop was concluded successfully. Now for phase two. At the end of December, a new high-wire cultivation starts in the Winter light greenhouse, with an aisle width of 1.8 m. Kempkes said, “Both 1.4 and 1.8 produced good results, but the plant damage was greater with 1.4.” The researcher, also project leader of the Winter light greenhouse, has high expectations of the follow-up study. “The Winter light greenhouse was recently completed and is truly a beautiful piece of work.” The construction is covered with a white powder coating with an increased reflection level of 90%. SmartGlass is used, a new type of diffuse glass measuring 300 x 167 cm. Even when the glass is wet or covered in condensation, the light transmission does not decrease. The integrated Iso++ screen system is mounted in a W-format for optimal light transmission when the screen is closed. The greenhouse is also fitted with a new, highly transparent screen material with even better light transmission. The greenhouse is fitted with an ‘Air in Control’ climate-control system. It was expected that the greenhouse would show a 10% gain in light. “The initial measurements revealed that this gain in light was achieved. The next crop is expected to indicate whether we can achieve 10% more production.”
In the highly insulated 2SaveEnergyGreenhouse, high-wire cultivation of cucumbers was tested last year. The project focussed on optimising a vegetable crop on the basis of the available, scarce winter light. During two crop rounds, researchers intensively monitored the light interception, cultivation (crop, production and quality) and energy consumption. The performance was good, and the test clearly showed that both energy savings and increased production are possible.
Text: Jojanneke Rodenburg. Illustration: Studio G.J. Vlekke