Grow light is gaining ground among high-wire cucumber growers. Reijm & Zn in Berkel en Rodenrijs in the west of the Netherlands are among the many who have recently ventured into lit cultivation. “Lots of colleagues are exploring grow light in cucumbers,” explains Reijm & Zn partner Jan Reijm. “Most people know by now what SON-T can do. We want to learn from a new concept with vertical LED lamps. It has lots of advantages, but there are limitations as well.”
The system that Reijm has been testing on a small scale since the end of 2016 was supplied by the Dutch company Lohuis Lighting & Energy in Naaldwijk, which has been specialising in LED lighting for many years. What catches your eye straight away is that the Saturnus Veg LED lamps are not suspended above the crop in horizontal fittings or strips but in vertical tubes hanging between the plants.
Representative and lighting advisor René Grootscholte: “A huge amount of research has been done into assimilation lighting with LED lamps over the past fifteen years. Reports from research institutions in the Netherlands and Belgium clearly show that vertical lighting concepts in climbing crops such as fruiting vegetables produce the highest lighting yield. And that’s quite logical: the PAR light emitted by lamps above the crop is intercepted by the top leaves, so the leaves half way down the canopy get very little benefit from the higher light levels. The middle of the plant also gets much less daylight for the same reason. Our lights transmit their light over a height of 1.15 metres, which is where it really benefits the crop most: not above but just below the top parts of the crop.”
Reijm & Zn in Berkel en Rodenrijs have been growing two high-wire crops per year on 4.5 hectares for four years now and were keen to test the new concept. “Many colleagues are exploring grow light in cucumbers,” Reijm says. “SON-T has been widely used for some time and we all know by now what it can do. The heat radiated from these lights prevents a number of potential problems in the crop, including Mycosphaerella in the tops. You don’t get that heat with LED lamps. On the other hand, LEDs are more flexible and can be used over a longer period in the year. There are often times when you want a bit of extra light without the extra heat.”
Another striking feature of these vertical LEDs is that they come with two settings with different light spectra. Besides the setting with the usual red/blue spectrum, there is a separate setting that only provides far-red light which has a similar effect to natural twilight, Grootscholte says. “This setting is mainly designed to light the crop with far-red light for an hour longer in the evening after you’ve switched off the standard lights – just as you’d get in nature, really. This activates the phytochrome and gets extra assimilates going to the fruits. In essence, you’re inducing the transition to the generative state.”
Attractive increase in yields
“We’re keen to learn from this vertical lamp with two settings,” Reijm says. “I’m interested to find out how far you can get with this kind of system. For us, growing under grow light is vital if we are to continue to compete against Spanish growers. The gain – or rather a better return per square metre – needs to come from better quality and better fruit colour in the darker months, as well as an attractive increase in yields. After all, it involves a considerable investment which you want to recoup within a reasonable period of time.”
Before planting their first artificially lit crop (28 December 2016), they installed lamps giving around 85 μmol/m2/s of PAR light at 55 cm intervals in each plant row in the 540 m2 trial section. That worked out at more than one lamp per square metre and about 95 μmol extra grow light, Grootscholte says. “We have just released an improved version that gives eight percent more light using the same amount of power.”
Higher light levels and more effective use of light by the crop deliver higher yields in various ways. “You can get more plants or stems per square metre or more fruits per plant,” Reijm says. “It’s all about getting the right balance between higher yields and fruit weight. We aim for regular production and an average fruit weight of around 420 grams.”
Results of the first crop
In their first cucumber crop under grow light, Reijm kept the stem density the same as in the unlit crop. This was originally 1.5 stems per square metre and was doubled later to three per square metre.
The plant load was different, however, as the grower explains: “We thin out every second fruit in the unlit crop. Because the plants can cope with more under grow light, we left a set of two fruits on the plant each time before removing the next one. So we ended up with roughly 25 percent more cucumbers on the plant, but in retrospect that was too many.”
The fruit weight was lower and because the plant load was too high, production was less regular. “We noticed a drop in growth rate quite early on, so we waited a while before leaving a second stem to grow. That meant that production lagged slightly behind the reference crop in the first phase, which wasn’t what we wanted, of course. Ultimately it more than made up for that, but it was obvious that there was room for improvement at the start of the crop. We were very happy with the colour of the fruits.”
The second crop was planted in mid-June. This time the young entrepreneur opted for a slightly higher stem density of three stems per square metre, compared with 2.5 in the unlit crop. “We thinned the fruits in the same way – alternately, in other words,” he says.
Because the crop was planted just around the longest day, in a period in which no artificial lighting was used, the fruit weight in the trial section was also slightly lower than usual to begin with. Reijm: “By mid-August we had cut 58 cucumbers of 408 grams per square metre in the unlit crop, compared with 67 of 375 grams in the lit crop. The LED system was on regularly from mid-June onwards. It clocked up quite a few hours, particularly in the first half of August, and you could see that quite clearly from the crop. It was healthy and strong and the fruits were nicer as well.”
With a few more months to go at the time of writing, the grower didn’t want to draw any firm conclusions just yet. “I know roughly what I can expect from a grow light system,” he says. Depending on the specifications and price and with two crops a year, you should be able to cut around 90 fruits more per square metre. “We’re not there yet, but that’s no bad thing. This is a year for learning and we have certainly learnt a lot already. We will also be keeping a close eye on how other growers are getting on. I’m still convinced that we can make headway with this system, and we’re certainly open to that.”
A new LED lamp hanging vertically in the crop enables climbing crops such as fruiting vegetables to get more out of the radiated light over a larger height than systems in which the lamps are positioned horizontally. The lamp has two settings with different light spectra. In addition to the usual setting with red and blue light, there is a setting for extra lighting with far-red light only.
Text and images: Jan van Staalduinen.
Brabant start-up Crux Agribotics has developed the world's first fully automated cucumber harvesting robot. The robot is unique because it also harvests cucumbers deeply hidden between the leaves of cucumber plants. The robot uses a machine learning algorithm, which allows it to independently determine which cucumbers are ripe for cultivation, and which cucumbers are diseased.
The harvesting robot consists of a trolley with rotating cameras and a flexible grab arm. The cameras make 3D images of the crop from a variety of angles, after which the robot uses special software to build up a complete picture of where cucumbers are located. The robot then sends the coordinates of each cucumber to the grab arm, which clamps the cucumber by the stem.
Since the robot visualises the crop from different angles, it also sees cucumbers hidden deep between foliage. Special software converts various images into a whole, and controls the grab arm. According to Richard Vialle, co-founder and director of Crux Agribotics, the robot picks 96 percent of all ripe cucumbers. A limited number of employees follow the robot to pick any cucumbers which are missed.
Vialle says that the data collected by the robot is very important. The robot uses a machine learning algorithm, allowing it to assess more accurately which cucumbers are ripe for picking. The grower is partly responsible for this learning process. According to Vialle, "The robot sends the grower a picture when in doubt, and asks what it should do with the cucumber in question." The robot also learns to recognise diseased cucumbers in this way.
Harvesting, sorting and packing
A major advantage of the machine learning algorithm used by Crux Agribotics is that a robot can also sort and pack cucumbers. However, the advantages of the algorithm do not stop there. Vialle says, “The learning algorithm means that the robot can also make predictions, such as how the cucumber will grow, or how many days before a cucumber is ripe."
On the market
Crux Agribotics has tested the fully automated cucumber robot with a number of growers, and is currently working on developing an industrial product that can be used anywhere in the world. “We need another two years for this, and are we looking for strategic investors," says Vialle. Crux Agribotics is also developing similar robots for pepper and tomato crops.
Text: Leo Hoekstra. Photo: Crux Agribotics.
Last year the focus in the Dutch 2SaveEnergy greenhouse was on high-wire cucumbers. Over two production cycles, Wageningen University & Research investigated whether it was possible to grow a crop that could intercept and use winter light to the full. This trial was a preliminary study in advance of upcoming trials in the Winterlight greenhouse, a design that lets in 10% more light in the winter.
The crop in the innovative greenhouse was very successful, say crop researchers Jan Janse and Frank Kempkes. It was cleared at the end of November and the total yield is estimated at 110 kg, with 260 cucumbers. “And all with minimal energy input,” Janse says. “We used around 17.5 m3 of gas over the entire year. That once again puts us well below the average for the sector.” Yet again, this new greenhouse proves what it is capable of. The concept clearly demonstrates that Next Generation Growing can be made even more energy-efficient without affecting production or quality.
Steering the crop
This high-insulating greenhouse at the Energy Innovation and Demonstration Centre in Bleiswijk features clear glass and a permanent, high light transmitting, diffuse layer of plastic film parallel to the glass. The greenhouse is fitted with a dehumidifier unit with outdoor air entering via ducts under the gutter.
The researchers planted the cucumber variety Hi-Jack in the greenhouse on 29 December 2015. The crop was steered by varying the row width and plant density and by thinning out the fruits, the optimum having been modelled in advance. Over two production cycles the team intensively monitored light interception, cultivation (crop, production and quality) and energy consumption.
Different row widths
Janse: “We decided to start with a plant density of 1.67 plants/m and three different row widths: 1.4, 1.6 and 1.8 m. Among other things, we wanted the trial to tell us which row width would produce the best crop, would be best for light utilisation and would be easiest to work in. After all, you have to be able to move through the cucumbers on the high-wire trolley without damaging the plants too much. Each setup consisted of three ‘carousels’ (growing gutters). Regular crop observations were carried out on one carousel in each setup.”
To record the observations, Kempkes took photographs from a fixed position above the crop at the same time once a week. Using an image processing program, the researchers were then able to track the development of the crop and the projected leaf surface area to get an idea of the amount of light being intercepted. Kempkes: “If you can see a lot of the floor or the gutter on the photos, light interception is not as good as it could be.”
45% less gas
At the end of January last year, the plants were doubled by pinching out. “At one point we had a crop with highly generative growth and small leaves, but we still harvested a lot of cucumbers from it. Over six weeks (weeks 15-20) the crop produced as many as ten cucumbers per week, or 4.5 kg/m2. So clearly the plants were using their assimilates very efficiently.”
According to Janse, even the two growers on the supervisory committee were looking enviously at the crop. “The plants were strong and production was high – better than in a commercial greenhouse, in fact. We still have some work to do to find out the exact reasons for this. It may be partly down to good crop care. What was also striking was the temperature achieved: it averaged 1ºC higher than in a commercial greenhouse. This meant that the cucumbers got going very quickly. Over the entire period, the development time was around 14 days at an average greenhouse temperature of 21.4ºC. The row widths of 1.4 and 1.8 m yielded the highest production. In addition, gas and pure CO2consumption worked out at 12.7 m3and 4.5 kg/m2 respectively. This represents savings on gas consumption of around 45% compared with commercial greenhouses.”
Later second planting
The team set up a new crop in mid-July. This time they used Hi-Power with a plant density of 2.25 plants/m2, again with the same three row widths. In the period with the most light, there was therefore a gap of three weeks between the end of the first crop and the start of the second one. “We deliberately planted it slightly later because we wanted to test the crop in the dark period as far as possible. After all, this was a preliminary trial for the Winterlight greenhouse. By the end of October we had already harvested almost 100 cucumbers from this second crop, with an average fruit weight of around 420 grams. The crop finished off well and we achieved excellent overall production of good quality cucumbers.”
This time too, the row widths of 1.4 and 1.8 m yielded the best results. So the objective was fulfilled. An excellent crop can indeed be achieved with a relatively small leaf surface area, in other words small leaves, a characteristic of the variety. Because the rows were oriented east-west and care had been taken to distribute the wires evenly, the crop clearly intercepted enough light and a good proportion of the assimilates went to the fruits. There was barely any fruit abortion. Smaller leaves also mean less transpiration, which saves energy in cold periods.
The research into an efficient Winterlight crop was brought to a successful conclusion. On to phase two: in late December 2016 a new high-wire crop was planted in the Winterlight greenhouse, this time with a row width of 1.8 m. Kempkes: “Both 1.4 and 1.8 produced good results but there was more plant damage with 1.4 m spacing.” The scientist, who also manages the Winterlight greenhouse project, is expecting a lot from the follow-on trial. “The Winterlight greenhouse was handed over recently and is really very nice.”
The entire structure is painted with a white powder coating with an increased reflection factor of 90%. The glass used is SmartGlass, a new type of diffuse glass in panes measuring 300 x 167 cm. Light transmission remains constant even if the glass is wet or covered in condensation. The integrated ISO++ screen system is fitted in a W shape for optimum light transmission when the screen is closed. In addition, the greenhouse is fitted with a new, highly transparent screen cloth with even better light transmission.
The greenhouse is equipped with an Air in Control climate system. The expectation was that the greenhouse would let in at least 10% more light. “Initial measurements have indicated that this light gain has in fact been achieved. The next crop will prove whether we can achieve a 10% rise in production too.”
Cutting energy consumption
In the meantime, the 2SaveEnergy greenhouse has been adapted for a new research project entitled “A strong crop with little gas”. The assumption is that it should be possible to go yet another step further in reducing energy consumption. Janse: “We will be trying this out with a dehydration system that recovers heat using a heat pump. This will enable us to not only recover tangible but also latent heat. There will also be three movable screens in the greenhouse and some adjustments will be made to the control strategy for the tomato crop.”
Both the 2SaveEnergy greenhouse and the Winterlight greenhouse are financed by the Greenhouse as a Source of Energy programme, the innovation and action programme of LTO Glaskracht Nederland and the Dutch Ministry of Economic Affairs.
A high-wire cucumber crop was grown in the high-insulating 2SaveEnergy greenhouse last year. The aim of the project was to optimise a vegetable crop by making use of the available scarce winter light. Over two cycles the researchers intensively monitored light interception, cultivation (crop, production and quality) and energy consumption. The crop performed well and the trial clearly demonstrates that both energy savings and higher production are achievable.
Text: Jojanneke Rodenburg. Images: Studio G.J. Vlekke.
By the end of June 2016, time was getting tight for cucumber grower Marco Zuidgeest. If he wanted to grow the innovative small core cucumber again this season, he would have to get an order to sow in soon. But the feedback from the customer was taking its time. Zuidgeest: “And with this sort of supply chain project, you can only move forward once everyone is happy. I’m a big fan.”
Zuidgeest has been selling cucumbers to the British company Greencore under contract via the Best of Four growers association for six years now. This convenience foods producer uses vegetables in ready meals, sandwiches, wraps, baguettes, sushi – you name it. The Food to Go division produces around 500 million pre-packed sandwiches per year. And what would a sandwich be without fresh slices of cucumber?
“Oh yes, they are a good customer of ours,” the cucumber grower continues. “We supply them with standard length cucumbers, and of course it’s always nice to have something special to offer. So I regularly ask the vegetable breeders whether they have anything new we can try.”
Cucumber crop coordinator Marcel van Koppen also heard his request, which immediately got him thinking about the variety 24-250 RZ. “Rijk Zwaan has been working on cucumbers with a smaller core for a while. Now we had a variety that came through our internal trials well. Marco wanted to try it out at his nursery, providing the customer agreed.”
Demand for “drier” cucumbers
The vegetable breeding company in De Lier already has several supply chain projects on the go and benefits from existing contacts with sectors such as the convenience market. “Our people keep in close touch with vegetable processing companies. You just have to think of lettuce for pre-packed mixes. The collaboration is mutual, by the way: we brainstorm, solve problems and come up with new products together.”
Special breeding programmes focus on aspects such as keeping qualities, colour and taste. “We started getting requests for a different type of cucumber some years ago. Processors wanted a slightly “drier” variety to use in sandwiches. As we all know, sandwiches with slices of cucumber in them often go soggy quite quickly. Ever since then, our breeders have been working on a fruit with a higher dry matter content. And a smaller seed core – the processing company removes this, so the smaller the core, the more flesh they have left over to use. Now that we have finally developed a potentially interesting variety, it’s time to put it to the test in practice: at Zuidgeest in the Dutch village Delfgauw.”
The cucumber grower had already tested the variety on 150 m2 last season. “We used it as an intermediate crop. It was quite difficult and we had trouble getting the crop balanced. It had a lot of foliage and weak fruits. But we realised that we could eliminate many of these problems by steering the crop separately. So this season we gave the small core cucumber a second chance.”
On 21 July 2016, Zuidgeest planted three rows totalling 1,000 m2. This time the crop did a whole lot better. “We harvested the first fruits on about 10 August and the last ones around 1 November. Of course there are differences. Compared with our main variety, this one produces around 15-20% less. But I’m not too worried about that now. At the end of October I picked a row myself and they were lovely, uniform cucumbers.” The diameter and weight of the two varieties is almost the same, the grower says. He aims to pick them at between 350 and 420 grams.
For the time being, Zuidgeest is harvesting the new variety separately. “Every day one of our regular staff members picks around 30 boxes, and we send two pallets off to the customer every two days. Having the same person harvesting these rows helps us supply a consistent size. We don’t sort this variety. We have agreed with the British customer that they will take all sortings. Look, there they are in those green crates.”
The Rijk Zwaan advisor picks up a sample out of a crate and compares it with a standard Lausanna RZ variety fruit. The first thing you notice is that the newcomer has a smooth skin. Otherwise it’s hard to tell the difference – at least until Van Koppen cuts the cucumber in half. Now the smaller core is clearly visible. He also squeezes a piece of the fruit. It produces quite a lot less water than when he does the same with a reference piece.
Only deliver perfect fruits
“Our customer has also seen that the fruit is drier, of course,” the grower says. “They recently sent a delegation over to visit us. You can tell straight away when someone is a trader and not a grower. For instance, I had to explain to them that a cucumber is a natural product and that you can’t simply harvest a specific sorting to order. I think they’d like to leave us a ruler so we only deliver perfect fruits! After all, they have done their calculations: ‘We are making x number of sandwiches, so we need y slices of cucumber and we get z slices out of one fruit, so we need so and so many fruits.’ I do my best, but of course it depends on a variety of factors. Fortunately they went away with a better understanding of how it all works.”
Sandwiches stay fresh for longer
Greencore sandwiches find their way to an average of 45,000 outlets per week across Great Britain alone, such as supermarkets and petrol stations. The sandwiches are sold under their own label. Both Zuidgeest and Van Koppen are looking forward to hearing what the company has to say about the new cucumber. Does this cucumber have a future?
Both the grower and the advisor firmly believe in the added value of this product. But if the customer doesn’t think the higher price is worth paying, it stops here and now. After all, the downside of this variety is its lower production.
Zuidgeest: “The small core cucumber has a lower yield and is more labour-intensive. But if you want to stand out, you have to try something new now and again.” Luckily the customer is also happy with the trial. They report that the quality and specifications are fully in line with their expectations. They are seeing less moisture loss from the product during processing, which is improving the quality of their sandwiches. Larger-scale trials will be carried out over the next few weeks. Van Koppen: “For companies like this, switching to a new type of cucumber doesn’t happen overnight. It’s not a question of weeks but rather months. After the crop, an extensive evaluation will take place.”
All parties benefit
The vegetable breeder is fully aware that the cropping traits of this variety still need work. “Our breeders are working on this at the moment. Variety development is a lengthy process, and with initiatives like this one you still have to contend with the trade-off between the different needs of the parties in the supply chain. The art is creating a range of vegetable varieties that both processors and growers can profit from to the max.”
In this kind of supply chain project, sharing knowledge is extremely important. Most of the contact between the grower and the customer takes place via the breeding company in De Lier. Zuidgeest: “They already have the lines of communication in place and they have special people to handle this. Afterwards, I get to hear from Van Koppen who wants what. It would take up too much of my time and energy to have to deal with that myself. It’s great that we can all work together this way. The breeder responds to current needs with new varieties, I can make my business as a grower stand out by offering a special cucumber, my customer can put sandwiches with added value on the shelves and the end customer gets a more appetising lunch. Here’s hoping this takes off!”
Marco Zuidgeest from Delfgauw grows the small core cucumber specially for the British food processing company Greencore. The characteristics of this fruit meet their needs perfectly. It’s a great example of customer-focused product innovation. To succeed, the project needs good communication between all the parties. With wants and needs being constantly fed back, improvements can be made.
Text: Jojanneke Rodenburg. Images: Leo Duijvestijn.
Paul Jeannet, farm manager of the UrbanFarmers rooftop greenhouse in The Hague, has used the Qlipr system for three months in four different crops: ‘It’s very easy to use, once you get used to it. It allows us to save time and - this is the biggest advantage in my opinion - we can reuse the clips after every crop cycle. We can easily separate the clips from the plants and compost the plants, because there are no strings or plastic clips left in it. Nothing is wasted.’
The Qlipr system fits right into the UrbanFarmers philosophy, which is based on creating added value and minimizing waste. At the UF002 farm in The Hague, consisting of a greenhouse with a surface area of 1,000 m2 on top of a former office building and a Tilapia fish farm, that philosophy has been taken into practice. The waste water of the fish tanks is turned into nutrients for the plants in the greenhouse. In the greenhouse, different varieties of lettuce, tomatoes, cucumbers, sweet peppers and aubergines grow in a hydroponic system. The water that is not used by the plants is purified and pumped back to the fish farm, which reduces overall water usage by 80%. Pesticides are forbidden; only biological plant protection methods are allowed. The products are sold to customers in the region, to minimise food miles. ‘We grow fresher, tastier and healthier products, as close to our customers as possible. And we minimise waste,’ Paul Jeannet explains.
The fresh revolution
Paul Jeannet (24) started working for Urban Farmers one year ago, after an internship at UrbanFarmers’ first farm (UF001) in Basel. He studied biological agriculture in Switzerland, before he joined ‘the fresh revolution’. ‘At first we were only growing lettuce and tomatoes. When our gastronomy partners told us that they would prefer more diversity, we took out some of the tomatoes and put in cucumbers, aubergines and sweet peppers instead, and several different varieties of tomatoes. We kept the lettuce section.’
It is quite different from the normal plastic clip we were using, but once you get used to it is very easy to use.
Six months ago Paul got in touch with Cor Pellikaan and became interested in the Qlipr system. ‘We wanted to give it a try to see if it would work in different crops. Three months ago we started using the system in tomatoes, cucumbers, sweet peppers and aubergines. As it turned out, the system is quite easy to use: we take the lower clip and place it on top and we lower the plant at the same time. It is quite different from the normal plastic clip we were using, but once you get used to it is very easy to use.’ The lowering schedule is once a week for tomatoes, three times every two weeks for cucumbers and once every two weeks for sweet peppers and aubergines.
Cor Pellikaan, the inventor of the Qlipr system, needed a pilot project to test his clips on sweet peppers and aubergines. Until three months ago, the system - which he invented in 1996 - was only used by growers of tomatoes and cucumbers worldwide. The system consists of a crop hook (1.40 meters long) and two clips. Halfway through the plants’ development, extra crop wires are needed with which to fix the crop hooks into place.
It will save labour, because you can de-leaf, remove shoots, prune and lower the plants in one go.
The main advantages of the system are, according to Pellikaan: ‘It’s very simple to use. Everybody can work with it. It will save labour, because you can de-leaf, remove shoots, prune and lower the plants in one go. This is also better for plant health, because there is less chance of damage.’ Paul Jeannet confirms that he saves up to six hours a week in the rooftop greenhouse because he uses the Qlipr system instead of regular plastic clips.
The main advantage of the Qlipr system is its durability, says Pellikaan. ‘My first client bought them 18 years ago and he is still using the same clips. Of course, you have to disinfect them at the end of every crop cycle, but that is very easy. You can use steam, chemicals or pasteurization. I recommend the latter, after two years of thoroughly testing this method. Just put the clips in a box on a trolley and cover it up with a canvas. Heat up four pipes to 60°C under it for three days. Works perfectly.’
Thanks to the Qlipr system neither plastic string nor clips are left on the plants after each crop cycle.
Paul says this is a big advantage too, but there is more. Thanks to the Qlipr system neither plastic string nor clips are left on the plants after each crop cycle. ‘So we don’t have to throw away our plants, but we can shred them for composting. It also makes it much easier for us to get rid of the plant material, because we have to transport everything via the lift.’
Qlipr versus traditional clips
How many clips are needed to bear the weight of the plants? ‘At the start of the season one clip will suffice. You attach it at 40 cm below the head of the plant. When the plants get heavier you will need to add a second clip, Cor Pellikaan explains. A new item in the Qlipr product range is the double-stop crop hook of 1.40 meters with two stoppers: one at 50 cm and one at the bottom of the hook. This makes it possible to use the same hook for tomatoes as well as cucumbers.
You buy it once and then you can use it every year.
The investment in the Qlipr system is higher than with traditional plastic clips, but they will last a lifetime, Cor says. ‘Also, you don’t need to buy expensive trolleys with hydraulic platforms, because the plant tips grow at a height of 160 cm. Therefore, cheap trolleys will suffice. In most cases this will save you enough money to buy Qlipr clips.’
Paul Jeannet has become a fan of the Qlipr system rather quickly: ‘Cutting leaves has become more enjoyable. We no longer have a plastic string or plastic clips at the bottom of the plant holding the leaves together. Only two clips at the head of the plant.’ Would he recommend this system to other growers? ‘Yes! It is a really interesting system to work with; you buy it once and then you can use it every year.’
Pellikaan thinks the Qlipr system will also benefit growers in the future. He is working on a mechanical system to pollinate crops without the use of bumblebees. It has been tested thoroughly and he expects to launch it this year. He is also working on a robot that can harvest and de-leaf tomatoes, which is still a prototype. That is still a bit of a secret, so we will stop asking here. It is clear that Cor Pellikaan is still coming up with new inventions for international horticulture to create simple solutions that work.
Plant bugs like the European tarnished plant bug and the common nettle bug are a serious problem in crops such as aubergine, cucumber and chrysanthemum. Even in small numbers they can do considerable damage: abortion of the flower in aubergines, stem and fruit damage in cucumbers and splits in chrysanthemums. As soon as growers spot bugs or bug damage, they feel they need to intervene fast with products that are harmful to the biological predators they are using for other infestations, marking the beginning of the end of their biological pest control.
Bugs usually enter the greenhouse from outside. They can arrive early in the season but most sightings of bugs, particularly the most harmful species, the European tarnished plant bug, are reported in the summer months. A good method of spotting and monitoring the presence of bugs can help growers decide when to use pest control products. It would be even better if bugs could be effectively eliminated from the plants with traps.
Pheromones and plant aromatics
A trap with a pheromone attractant for the European tarnished plant bug (Lygus rugulipennis) was originally only available for outdoor use, mainly in strawberry crops. Producers of biological pest control Entocare biocontrol C.V. and Wageningen University & Research have been working with a number of growers in the Netherlands to study and optimise the use of the trap and pheromone in the greenhouse. This trap is now available for detecting the presence of the European tarnished plant bug in various crops (aubergine, cucumber).
The traps were tested in a season-long trial and show peaks in the occurrence of bugs (Figure 1). The relationship between the numbers of bugs caught and the damage they cause is currently being investigated more closely. The level of the peaks and the increase or decrease in the numbers captured in weekly counts help the grower decide which crop protection measures to take.
Trapping bugs certainly helps control them but as yet it is unclear what proportion of the bugs already present can be eliminated with traps. The distribution of bugs across the greenhouse is very irregular: catches in traps show no evidence of bug hotspots.
During the trial it was discovered that the luring effect of the pheromone works best in the presence of plant or crop aromatics. A simple pheromone trap catches fewer bugs than a trap with the smell of the crop in the background. But it is mainly the males that are attracted by the smell of the pheromone, so the researchers have set about finding attractive alternatives to lure females as well. Their main focus is on plant aromatics.
Several plant substances that seem to attract the females have already been identified. Lab trials indicate that the concentration at which the aromatic is offered is critical, however (Figures 2 and 3). Too little fails to attract them while too much scares them off. Some substances are attractive to both males and females (substance B) while others only attract males (substance D) or only females (substance A). The research is now focusing on finding the right substances, or combination of substances, and on finding a formulation that will go on producing the right intensity of aromatics over a long period of time in practice.
Trap colour and shape
The funnel trap with pheromone which researchers are currently using needs to be further optimised for catching bugs. Video recordings of males landing on these traps showed that less than five per cent of landings on the trap actually resulted in capture. The colour and the shape of the trap will be studied in more depth in future research, along with ways of further optimising the trap. If a combination of pheromone, plant aromatics and better traps proves successful in trapping both males and females, this will open up new opportunities for tackling the bug problem.
Besides observations, the aim is also to improve biological control with an effective combination of attractants and biological agents. To begin with, the researchers are looking at a biological agent based on an insecticidal (entomopathogenic) fungus. They are investigating whether it is possible to use attractants to target fungal spores better in the crop in order to increase their effectiveness in controlling bugs. With a modified formulation of the fungal spores and an effective method of transferring them to the bugs, it has been shown that it is possible to get at least three to four times more spores onto a bug.
The next question is whether this combination of methods (luring, infecting and transferring) actually helps combat the infestation. Further research on this will be taking place during the coming year.
For some years now, scientists and growers have been working together to come up with a better monitoring and control plan for the European tarnished plant bug. A pheromone trap that captures males has already been successfully tested. Research into attractants for females has yielded some new substances that are effective, offering new options for controlling this bug.
Text and image: Rob van Tol (Wageningen UR), Maedeli Hennekam and Daowei Yang (Entocare biocontrol).
Hans Houben’s initial reason for trying out Next Generation Growing was to save energy. “But that shouldn’t really be your main objective: you need to focus on the plant,” the cucumber grower says. This has led to a higher 24-hour temperature, growing with the light, more screening and adjusting for outgoing radiation. Oh, and lower gas bills too.
Every year is different when you use the Next Generation Growing (NGG) method. You keep taking one step further and all of a sudden you’ve created a completely new way of growing. “I am always very keen to keep up with the latest developments, but to begin with I was quite sceptical. It all sounds very logical but it takes courage to do it. Right now I’m starting venting on the wind side, for example. It is working out well: you get a much more even climate and it’s easier to keep the humidity at the right level. But I really wouldn’t have done it this way two years ago,” Hans Houben says.
His screening hours have also increased: he is now screening twenty per cent more than in his second NGG year. “During the first couple of years you tend to be a bit wary of doing things this way. Before I started I used to mainly keep an eye on relative humidity, but now it’s all about absolute humidity, humidity deficit, vapour pressure and outgoing radiation.”
Back to the plant
Hans and Carla Houben’s cucumber business Mellantas in Sevenum (4.7 ha) in the south-east of the Netherlands is on its third season of high-wire cucumbers. At their old site they had two crops of cucumbers per year, followed by autumn tomatoes. After moving to their new location they introduced high-wire cultivation with two crops per year, first Topspin and then Kurios. The plants grow in rockwool that lies on the ground.
Gas consumption is currently at 28.5 m3/m2 for production of 230 cucumbers per square metre. A traditional crop would use 34-35 m3/m2 for 180-195 fruits. “The power of Next Generation Growing lies in the fact that you are going back to the plant,” Houben says. “We have started growing more quickly, with a higher 24-hour temperature, but we keep the plant load at no more than 6-7 cucumbers per plant. From 11 am onwards we allow the temperature to get higher than before, light permitting.”
For example, with 1,000 watts of incoming radiation the 24-hour temperature is 21.5ºC, and with 500 watts it is 19.3ºC. In his first two years of NGG, Houben allowed an extra 1.5ºC per 1000 joules of incoming radiation over and above the basic temperature of 18ºC. Now it is 2.5 to 3ºC extra – so quite an increase. He achieves this with a combination of heating, screening and ventilation.
“An extra 1.5ºC saves more energy, of course, but it makes the crop more sluggish. When it’s sunny we want a higher temperature, preferably 28ºC after 11 am rather than 25ºC, light permitting.” Before 11 am he aims to achieve a moisture deficit of 1.5-2 g/m3 to activate the crop; after that he works up to a higher temperature in a gradual line. “I used to turn the temperature down sometimes if there was a lot of light. But I don’t do that any more. You can tell by the top of the plant whether you are doing the right thing. If it is getting too thin, the 24-hour temperature needs to come down.”
If the temperature is higher during the day, the night temperature can be reduced slightly, although it is the overall 24-hour temperature that counts. Less use of minimum pipe prevents excessive evaporation and limits night-time energy consumption. Incidentally, the main source of heat is the grow pipe, which is always level with the fruits, and not the pipe rail.
More outgoing radiation
Over the past few years the grower has started screening twenty per cent more to limit outgoing radiation. He uses a very light Luxous energy screen from Svensson which only screens out twenty per cent of the light. A radiation meter (pyrgeometer) on the roof helps control the screens. There is also a thermal camera pointing at the crop. This isn’t connected to the climate computer but is used as an additional adjustment tool. Houben demonstrates how it works on the computer screen. “This morning there was a rain shower just after we opened the energy screen. You can see on the thermal image that the temperature at the top of the plants dropped to 15.5ºC at that point. You want activity but the tops of the plants are cold. So I closed the screen again and within ten minutes the temperature at the top of the plants had risen by 4-5ºC. That’s because you are eliminating outgoing radiation.”
The principle is simple. When outgoing radiation is higher than what is coming in, the screen is closed, even on a warm summer’s day. “In that case you close it ninety per cent. Then you can control the temperature easily and control outgoing radiation at the same time,” he explains.
The numbers always add up. For example, if there is 200 watts of radiation coming in, the screen blocks out 40 watts of that. But with a clear sky, outgoing radiation from the crop soon reaches 80 watts, and because that is more than 40, the screen has to be closed.
Houben has invested in a pyrgeometer, a thermal camera, a leaf temperature sensor and an extra sensor unit above the screen, but not in air handling units, extra fans or a second screen. “I could save an extra 2-3 m3 of gas with a second screen, but then I’d need a dehumidification system as well. The maths wouldn’t necessarily work then. So we decided not to do that just yet. We are waiting for dehumidification technology to move in a clearer direction,” he says.
With the experience he and other growers have gained, Houben sees potential to improve the system even further. “There is definitely scope to optimise the light/temperature ratio. You might be able to grow even faster with more light. If you can pluck up the courage, you could turn the temperature down more in the evening because you would still be achieving the 24-hour temperature, and that’s what counts. So an extra pipe during the day and not at night. But you could even raise the 24-hour temperature, which would enable you to maintain a higher temperature at night and make better use of the screen. And on sunny days you could also extend the day by switching to the night temperature later.”
Houben is also trying to gain a better understanding of the minimum level of evaporation needed at night. He is very happy with the knowledge shared on the LetsGrow platform. “I am learning a huge amount by looking over other growers’ shoulders. You don’t have to find it all out for yourself. You can see exactly what time other people open their screens and what that achieves. Next Generation Growing is really still in its infancy. You can get much more out of it if you focus primarily on the plant.”
High-wire cucumber grower Hans Houben is heading ever further down the path of Next Generation Growing. He has started screening more and keeps an eye on absolute humidity, humidity deficit, vapour pressure and outward radiation levels. His 24-hour temperature is up and it could even go a little higher. He is doing all this with one screen and no air handling units or extra fans.
Text: Tijs Kierkels. Image: Wilma Slegers
Recently, harvesting of cucumbers started in the new Winter Light Greenhouse at the Greenhouse Horticultural Department of Wageningen University and Research Centre in Bleiswijk.
The High-Power (Nunhems/Bayer) cucumber variety was planted on 19 September. Thanks to the good weather, the crop matured rapidly in this light greenhouse, so the first examples could already be harvested on 11 October. These first fruits were remarkably long; at the start of the harvest, fruits tend to be short. The growers who visited this test site every two weeks noticed that the plants were strong, with good ovaries and large leaves at the base. Although the greenhouse transmits more than 10% extra light in comparison with a standard greenhouse, light is still a limiting factor in this period. With the acquired knowledge, a second crop was planted immediately after Christmas.
The Winter Light Greenhouse is a new greenhouse concept which, in combination with a new type of screen system, new screen cloth and light-diffusing glass, improves light transmission by more than 10%. The entire newly-designed greenhouse structure is provided with a white powder coating, which offers an increased reflection factor of 90%. The greenhouse is glazed with SmartGlass, a new type of diffusion glass with large panels. Even if the glass is wet or covered in condensation, light transmission remains constant. The integrated Iso++ screen system is mounted in a W-shape for optimal light transmission when the screen is closed, and features a new Ludvig Svensson screen with even better light transmission. The new greenhouse design is also fitted with an Air in Control climate system.
The Winter Light Greenhouse was developed by a consortium of BOM Group, Ludvig Svensson, Bayer Crop Science and Glascom Tuinbouw, in collaboration with Wageningen UR. The project was also assisted by the Greenhouse as Energy Source (Kas als Energiebron) programme, LTO Glaskracht’s innovation and action programme, and the Dutch Ministry of Economic Affairs.
Source/Photos: BOM Group.
BOM Group will present a completely new greenhouse concept at the Greentech: the Winterlight Greenhouse. This concept, in combination with a new type of screen system by Svensson and light-diffusing glass, yields 10% more light.
The Winterlight Greenhouse, with all its installations, systems and products is currently built on the site of Wageningen UR Greenhouse Horticulture in Bleiswijk and will measure 500 m2. This coming winter the greenhouse concept will be tested with a new cultivation method for a cucumber crop, focusing on the winter period. Crop trials are conducted with the cucumber variety Hi-Jack. This variety is especially suitable for winter cultivation because of its leaf shape and direction.
The newly designed greenhouse structure is fully powder coated in white with an increased reflection factor of 90%. The greenhouse is glazed with SmartGlass, a new type of diffuse glass, sized 300 x 167 cm. Even if the glass is wet or condensed, the light transmittance does not decrease. The integrated Iso++ screen system is installed in a W-shape for optimal light transmission in closed position and is equipped with a new high transparent screen fabric of Ludvig Svensson with an even better light transmission. The new greenhouse concept is also equipped with an Air in Control climate system (overpressure air).
The Winterlight Greenhouse was developed in collaboration with Wageningen UR, Svensson, Bayer Crop Science and Glascom Horticulture. The project has been made possible by the program Kas als Energiebron, the innovation and action program of LTO Glaskracht and the Ministry of Economic Affairs.
BOM Group will present the new greenhouse concept at the GreenTech, hall 8, stand 108.
Agro-Invest is a turn-key greenhouse project in the Kaluga region, a special economic zone located 300 km from Moscow. The first 20 hectare of the in total 100 hectare greenhouse complex has been in practice for 18 months. Partners Dalsem and Hoogendoorn have captured this inspiring project on video.
The Agro-Invest project is a state of the art greenhouse with high-tech systems of Dutch origin. Among its features are a 40 MWe power plant for generation of heat, power and CO2, high light levels and intermediate plant lighting, irrigation water re-use, integrated propagation area with own seeding and germination facilities and a grading system suitable for all type of cucumbers and tomatoes.
The greenhouse comprises 10 ha for the production of tomatoes (four varieties: one beef tomato variety, one vine tomato variety and two varieties of cherry tomatoes), 8 hectares of cucumbers and a 2-hectare propagation area for young plants and seedlings, plus a packing area/irrigation room and an energy building. This greenhouse complex will make a tangible contribution to the region’s goal of becoming self-sufficient in the production of vegetables in the longer term. This is the first stage of a project that will ultimately comprise a total of 100 hectares of greenhouse on 238 hectares of land.
Source: Hoogendoorn Growth Management/Dalsem.