Know-how
Calculation model accurately predicts increased production with AntiReflect

In advance of practical trials, Wageningen UR has calculated the extent to which production increases under AntiReflect. The outcomes are very much in line with early practical results.

Increased vegetable production under AntiReflect accurately predicted

 

When developing new coatings, it is important to be able to quickly estimate the benefits for the grower. Mardenkro sets great store by independent assessments and has all new coatings analyzed in the light lab of the Greenhouse Horticulture Business Unit at Wageningen University & Research in The Netherlands as a matter of course. This provides an accurate picture of their physical properties. After that, the question is how the crop will perform under a new coating. Model calculations can predict performance well and produce results much faster than practical trials.
Once the new AntiReflect coating was ready for use in practice, Wageningen UR calculated the effect it would have using the Intkam crop model. The practical trials, which have been running since 2015, confirm the outcomes.

Photosynthesis and growth

“Intkam is a calculation model that calculates growth, development and production of greenhouse crops. We have been using models since the 1970s and we have been constantly refining them. So we can now say that we have built up decades of knowledge,” researcher Anne Elings explains. “At the heart of the model are the photosynthesis, respiration and development rate calculations. The outcomes of these calculations are translated into growth and production.”

Some processes are the same in all crops, such as photosynthesis, while others are crop-specific, such as leaf, flower and fruit formation. The researchers enter the crop, the cultivation strategy and the climate details into the computer model. To achieve reliable results, good crop knowledge is essential. Intkam now works well for tomato, cucumber, sweet pepper, rose, gerbera and chrysanthemum.

Using extra light

Light that falls on the greenhouse roof can pass through the glass (transmission) or it can be absorbed or reflected. The AntiReflect coating reduces reflection so that more light is transmitted through to the crop. According to measurements in the light lab, the light gain is 3% to 4% in all seasons.

To calculate what the crop can do with that extra light, you first have to know what effect it has on the greenhouse climate. This is calculated with another model: Kaspro. “Our colleague Frank Kempkes calculated the effect of AntiReflect by the hour for a whole year based on data on the outdoor climate and the characteristics of the greenhouse. This resulted in a light profile for the year, consisting of diffuse and direct light, PAR (photo synthetically active radiation), NIR (near infrared thermal radiation) and UV radiation,” he says.

This light profile and the climate data were entered in Intkam to calculate photosynthesis at different heights in the crop for every hour of the light period. The results were added to the photosynthesis for the entire crop. “This gives you a certain amount of growth per day. The next question is how the plant distributes the assimilates among its organs. This calls for in-depth knowledge of the crop, and we have built this up over the years,” says Elings.
In practice, model calculations often need to be fine-tuned for different nurseries because every grower grows in a slightly different way. “It therefore helps to give the increase in production in percentages. For example, production of a standard crop of tomatoes under AntiReflect is 3.2% higher than without a coating, and 3.4% for chrysanthemums,” he says.

Extra light welcome in winter

Extra light makes more difference if the light level is not very high to begin with, such as in the winter months. This mainly has to do with the way photosynthesis works. Photosynthesis increases rapidly as light levels increase but it plateaus once the intensity reaches a higher level. Every percent of additional light makes a big difference in the upward phase, but it has less effect in the level phase. “That is also the reason why roses perform less well than chrysanthemums under AntiReflect, with a production increase of just 2.8%. We took a based our calculations for roses on a higher level of assimilation lighting. Extra light doesn’t make that much difference in that case,” the researcher explains. On the other hand, the rose mainly sends the additional assimilates obtained from the extra light to the harvestable parts. That balances out the difference.

The highest increase achieved under AntiReflect is in cucumbers, at 5.1%. This is because the extra assimilates go mainly to the fruits. The two other crops calculated with Intkam were sweet pepper and gerbera, with increases in production of 2.9% and 2.6% respectively.
Elings: “The more light there is, whether it is natural or assimilation light, the greater the effect of AntiReflect will be. Combating reflection also seems to help at higher light levels, when photosynthesis plateaus. The increase in production is achieved in almost all months.”

Read more:

Practical tests confirm higher production under AntiReflect  

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