Glasshouse technology - smarter growing

June's inaugural GreenTech show highlighted the latest developments in glasshouse systems and equipment, Gavin McEwan reports.

Futagrow: glasshouse vegetable-growing format claims a 20 per cent better yield than traditional systems - image: Metazet/Formflex
Futagrow: glasshouse vegetable-growing format claims a 20 per cent better yield than traditional systems - image: Metazet/Formflex

The current travails of the domestic Dutch glasshouse sector have pushed the Netherlands' systems and equipment developers to promote to the international market as never before. The inaugural GreenTech show held in Amsterdam last June was intended as a major shop window for this, with the event's innovation award representing the pick of recent developments.

Announcing the winners, jury chairman and former president and chairman of Wageningen University & Research Centre Aalt Dijkhuizen told gathered industry figures: "If you are feeling pessimistic, you should join a jury like this."

The awards were divided into equipment and production categories, with the ID Kas super-insulated glasshouse from Technokas and partners Duijvestijn Tomatoes, Boal Systemen and Scheuten Glas taking the equipment and overall titles.

Technokas director Peter Zwinkels said: "It has 100 per cent insulation yet the light levels are no less than for a conventional glasshouse. No other Venlo-type glasshouse is able to use so little energy with the same light conditions. This means it can be heated with low-grade heat, such as geothermal or heat from other industries."

With double panes of diffuse glass and an anti-reflective coating, it achieves 93 per cent light transmission and can bring energy savings of up to 60 per cent along with increased productivity. Technokas project engineer Freek Batist added that one challenge to overcome was that insulation meant snow on the roof did not melt as quickly. But though strengthened, it is still lighter than a conventional structure.

"The structure and installation cost much the same, though the glass is obviously more," he said. "But you are using much less energy so you can repay your investment within seven years." Dijkhuizen pointed out: "They won for a few reasons. They worked together with the end user and every detail was looked at and optimised."

Filtering incoming light

Providing a temporary and more affordable means of diffusing light, French coatings company Sudlac was nominated for its OptiMix, which also reduces heat by filtering incoming light.

Head of product development Marcel Schoondergang explained: "In a country like Holland you want high light transmission to maximise plant growth. With this you can reduce temperature by screening out the green light without reducing photosynthesis." It can be sprayed on glasshouse roofs with conventional sprayers then washed off with cleaning agents, he added.

Another Technokas entry, the Daylight Greenhouse, was also nominated. This reduces heat around the crop without the need for screening by employing Fresnel lenses in the roof to focus excess solar energy onto water pipes. The water thus heated can then be stored underground and later recirculated as a heat source during colder weather or used to generate electricity.

Increased yields

Winner of the production category was the Futagrow glasshouse vegetable-growing format from Metazet/Formflex, which claims a 20 per cent increase in yield over traditional systems while using 15 per cent less water. The interchangeable two-tier system allows workers to harvest from the lower-tier gutters while standing beneath gutters of immature plants above. Growing purely in water rather than in stone wool makes the gutters lighter.

After nine weeks, the crops are swapped, with the next immature crop being raised above the by now mature, harvestable plants. With the system in use throughout the year, five or six crops can be raised, while the need for labour is levelled out across the year, the company says, claiming a return on investment within three-and-a-half years.

Managing director Arjan Kouwenhoven described it as "allowing the optimum use of space and light", adding: "We have been testing this for three years and are now ready to put it into practice. Now it's hard for Dutch growers to get money from the banks, but we have had a lot of interest from countries like the USA and Australia." The group was also nominated in the equipment category for its Activair system, developed with Priva.

Perhaps unsurprisingly, LED systems featured in both of the seminars (see box) and among the award nominees. Dutch electronics giant Philips was nominated for its GreenPower LED top-lighting module, which can be used either to supplement existing glasshouse lighting systems or to replace them completely.

It is very much designed for "intelligent" applications and comes with extensive support and advice on crop-specific light recipes from Philips' technical experts. The company suggests out-of-season strawberries, leafy salads and herbs as well as high-wire salad vegetables as suitable applications for the modules.

Swedish firm Heliospectra's On Target software, meanwhile, combines environmental sensor monitoring with predictive algorithms to help LED systems to compensate for a lack of natural light. "It plugs into existing glasshouse control systems and saves you energy while maintaining crop quality," the company explained.

Using light rather than chemicals to influence plants

Wageningen University & Research Centre lead glasshouse researcher Tom Dueck has pioneered the use of LEDs in commercial horticulture.

He told an audience at GreenTech: "You want homogeneous light distribution in the crop - that's something we have to work on. But you also want to get the balance right between vegetative and generative growth. Plants have different types of light receptors - phytochromes, cryptochromes and phytotropins - that are activated by different wavelengths."

He explained that the redand far red-sensitive phytochromes control germination and flowering, while the blue-sensitive cryptochromes govern photoperiodism and phytotropins the plant's orientation.

"We are looking at how different wavelengths at different times affect plant development. We can even increase vitamin C in tomatoes by growing them in LED tubes and are looking at how this might be done at crop level. The question of how you influence plants with light rather than chemicals is opening up new fields for us." But on LED interlighting trials in tomatoes, which he has overseen (Grower, 13 September 2013), Dueck added: "They are not always giving the crop boost that they should - it's something we are looking at."

Such steering of plants' development can be done alongside conventional high-pressure sodium (HPS) lighting, said Netled general manager Niko Kivioja, because the Finnish manufacturer's Booster hybrid lighting units "let you maximise efficiency during the season" at substantially less than the cost of a full LED lighting system.

"Blue-enhanced" systems can control a range of plant behaviours from leaf colouring to disease resistance while the tendency for leafy greens and seedlings to stretch under glass can be compensated for, he explained.

"Additional blue light also increases root mass and nutrient uptake," said Kivioja, and it may improve pollination in crops such as tomatoes. "Blue light may help bumblebees to see better. But they tend to fly toward conventional HPS lighting and die." The modules are already being used in five greenhouse locations in Finland and in the UK.

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