Hothouse of development

At what point does extra light no longer increase plant mass? The latest kit from Holland can tell you this and much, much more.

It’s not a landscape the Dutch Masters would have recognised, but the vast expanse of glasshouses in the Westland region of the Netherlands makes up one of the largest concentrations of horticultural production and development in the world.
Economies of scale, co-operation between growers and a healthy dose of government support have helped to keep the area at the cutting edge of horticulture.
Growers from other countries see Holland as a bellwether for the industry. Horticultural consultant Cas van den Berg says Chinese growers have begun modelling their greenhouse production on Dutch examples.
Here we look at five new technologies that have been developed in Holland.

Growlab Plantivity sensor
One problem with monitoring growing conditions is knowing how well the target temperature, light level, moisture and so on suit the crop in practice. The Growlab Plantivity sensor from Hoogendoorn Automation enables the grower to monitor growth activity.
By periodically firing a reflecting beam at a representative leaf, it calculates how actively the plant is photosynthesising. From this, the software — which is specific to the plant being grown — calculates how much dry matter the crop as a whole is producing per hour.
Hoogendoorn Automation UK general manager Mark Chivers says: “The aim with this and other sensors is to get a ‘talking plant’ that lets you know how much water content it has, the leaf temperature, sap upflow and so on.”
He adds: “The use of plant sensors is not new as such, but their use in the UK is still very limited. Most growers use only three or four sensors.” The Plantivity meter is not yet available in the UK.

Plant and environmental data monitoring
Sensors have so far been used in glasshouses largely as part of a feedback loop to tell the climate control computer whether target levels are being met and whether to take corrective action. But they also enable growers to analyse growing conditions retrospectively and work out how adjusting them affects plant growth and vitality.
Growlab was formed five years ago and is a collaboration between Grow Technology, which provides the software and plant expertise, and Hoogendoorn Automation, which provides the hardware.
Its GrowWatch stations use Hoodendoorn Automation’s light sensors, which measure up to 12 physical variables, including: photosynthetically active radiation; conductivity; crop temperature (via infra-red cameras); relative humidity; CO2; and air temperature.
As well as sending readings from these sensors every five minutes, the stations calculate 11 further “virtual sensors”, derived from the primary sensor data. These include non-photochemical quenching and vapour pressure deficit. Fortunately, Grow Technology also provides advice on plant physiology to make sense of it all.
This voluminous data is transmitted by ADSL line to a central data store in Amsterdam. It can then be uploaded and the effects of growing conditions on plant growth evaluated. Grow Technology marketing manager Hans Hein says: “You check all the factors to find out which is the limiting factor.”
He adds that such careful monitoring helps with pest and disease control. “Mildew, for example, is a climate problem. Treating it with chemicals is dirty, dangerous, expensive and stresses the plant. it is much better to tweak the relative humidity and so avoid it before it develops.”
Villa Rosa, a 4.5ha rose nursery in Honselersdijk in the Westland region, has been working with the GrowWatch system for a year. Co-owner Ron van der Knaap says: “We can learn from the data itself — for example, at what point does extra light no longer increase plant mass? We also learn from other users of the system via a user group. It’s about getting a better insight, increasing yield and avoiding mistakes.”

Solid state weather station
Grow Technology develops control systems using sensors of all kinds, including some that were not designed with horticulture in mind. The Airmar weather station, from the boating world, is one such innovation. The US-made, solid-state, ultrasonic device measures wind speed and direction, temperature, pressure and relative humidity.
Hein says: “Many growers have  weather stations on top of their glasshouses, but moving parts limit their lifespan. You have to get up there and maintain them or the data could be nonsense.”
Hein concedes: “The solid-state weather station is not cheap — around £700 — but we select on quality, not price. It’s stupid to save on sensors if they give the wrong signals. So we’ll experiment with it for a year and develop an interface that will allow it to integrate with other systems.”

Radio-optically controlled plant monitoring
Rijnplant’s 8,000sq m Anthurium “factory” at Berckenrode in Westland uses a complex plant monitoring and dispatch system. The 25,000 pot anthuriums in the stock buffer at any time each sit on a small plastic
“foot” housing a radio frequency identification tag, which allows GrowOrder, the stock control software, to pinpoint it and assign attributes to its “plant passport”, such as variety, colour, height and number of flowers. These each sit in one of 450 gantries controlled by conveyor belts.
The really impressive part is that the plant information is gathered entirely automatically as the pots regularly trundle through a visual detection unit, which uses multiple cameras positioned at different angles to identify the plant’s characteristics.
When an order comes in for a thousand plants of a particular variety with just three pink flowers, the computer-controlled conveyor belt network delivers these from whichever gantry they happen to be sitting on to the dispatch area — again with no human intervention and with accuracy exceeding 99 per cent. Watering is also regulated automatically.
Sales manager Martine van Rijn says: “It means a 50 per cent saving on labour and 100 per cent use of the available space.” The system was developed by WPS Horti-Systems and Grow Technology.

Energy-producing glasshouse
Worries about the rising cost of energy led to the launch of a government-backed competition in Holland last year to find ways in which glasshouses could move from being energy consumers to energy producers.
One of the most promising developments in this direction is a 5,000sq m prototype glasshouse in the town of Bemmel, run by ornamentals grower Stef Huisman BV and completed in May this year.
The glasshouse is divided in two. One half is heated and cooled conventionally. The other half incorporates 150 fine wire heat exchangers, being deployed for the first time in a production glasshouse, which transfer heat energy from the air in the glasshouse to water held in pipes. This is then circulated to an underground storage tank, from where it can be pumped back up when the ambient temperature drops.
Owner Stef Huisman reports that during recent warm weather, when outside temperatures reached 30?C, the temperature in the demonstration glasshouse — unlike in the neighbouring control glasshouse — remained at 25?C.
Netherlands Foundation for Glasshouse Innovation project manager Hans Koehorst says: “More heat energy goes into the glasshouse in summer than is needed in winter. The next problem is how to use that surplus energy productively. The water isn’t warm enough to heat a house but it could, for example, heat a sports facility.”

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