Published 30/07/2015

Energy savings with Next Generation Growing Eggplant: Observing the plant’s balances brings new findings

In autumn 2013 the project, The Next Generation Growing Eggplant, began on the 11.5 ha Greenbrothers nursery in the Dutch village of Zevenbergen. The project covered an area of 36,000 m2 and was supervised by TNO, the organisation that integrates science into society. As well as resulting in considerable energy savings both in the trial greenhouse and the reference greenhouse, it also provided the three brothers Johan, Frank and Ben Groenewegen who run the nursery, and other growers with helpful information.

In-Greenhouses-Energy-Saving-Next-generation-Egglplant_GrowerOne year later the decision to apply the project to a commercial nursery appeared a positive one. Eleven Dutch and four Belgian eggplant growers (covering 90% of the total eggplant area in the Benelux), and supported by suppliers, advisor Peter Geelen and project leader Joel van Staalduinen of Inno-Agro, were able to make large steps in a short time. They believe their involvement can yield even more so the whole group meets once every four to five weeks. On the nursery the trial is supervised by Frank Groenewegen and his production manager, Henk van Gurp.

Large steps without investment

The two-year project is funded by the growers, the suppliers who provide financing, time and materials and by means of a contribution from the program Greenhouse as Energy Source. Participants can follow the cultivation strategy via Let’

The trial greenhouse is equipped with two horizontal air hoses at the top of the building that are connected to two air handling units that can dehumidify the area under closed screens. It also includes Verti-Fan vertical recirculation-units and a double screen with Luxous 1347 FR cloths. The reference greenhouse contained just one screen. May-June 2014 vertical fans were also installed here as a result of the positive results. And in 2015 a second screen was also installed here.

“During the preparation year I, along with half of the growers, thought that technology was the solution. I even questioned if other growers should have to pay,” says Frank Groenewegen. “Now it turns out that it is not only about technology, but more about understanding the new insights, so that even without making any investment large steps can be made. With the contribution made by the individual participants everyone has the opportunity to share the knowledge and to earn back the ‘investment’.”

More screening

During the first year of the Next Generation Growing trial, the aim was to save energy by optimisation: more screening, less heating and moisture control under the closed screens. In this respect the eggplant grower made large steps. “In the trial greenhouse we went from 1,500-2,000 screening hours to 4,500 hours with a single screen and 3,500 hours with the second screen. Screening in the reference greenhouse increased to 4,000 hours.”

That can be seen in the savings in gas consumption. Commercially, the average gas consumption is 34 m3/m2. In the reference greenhouse it was 29 m3 and in the trial greenhouse just 24.7 m3. Before the trial started the grower’s energy consumption was actually quite high at 39 m3 of gas. “That was partly due to when the cogenerator gave us a good return. We hadn’t learned to save energy and so we did things wrong. I didn’t look at the plant and the climate, but at the rail temperature. Now, by screening on the basis of appearance I not only save energy I also have a healthier crop.”

Air hoses at the top of the trial greenhouse are attached to two air handling units that dehumidify the area under closed screens.

Air movement

One of the principles of Next Generation Growing is not to stimulate transpiration with the heating but via air movement when the screen is closed. This air movement ensures a continuous supply of energy along the plants so that they continue to transpire.

Groenewegen previously kept the rail temperature at night at 35ºC (95ºF) and at 38ºC (100ºF) in the early morning. “The plant transpires and cools off. Therefore you have to heat and, when it gets too warm, open the screens.” Now he screens on the basis of appearance. “We close the screens as soon as the sun goes down or by less than 250 watt radiation. Due to the use of the vertical fans the plant remains active enough. I’ve noticed that the quality of the crop remains good. The leaves are finer and thinner than normal. This is positive because then the sugars are also transported off well.

No use of minimum rail

According to Geelen the air movement also results in a uniform climate, without condensation. This prevents fungal problems. “A crop under a cold greenhouse roof will give off heat by radiation towards the cold greenhouse roof. If the screen is closed, the top of the plants remains warm. In this way you prevent condensation in the top. In addition the top receives calcium and sugars creating healthier and stronger cells,” explains the advisor.

The new approach resulted in the aubergine grower having fewer problems and more class 1 product. For the December planting (later than the trial) this new knowledge was also converted into more production.

Groenewegen did not use the minimum rail during the last year. As a result the fruit temperature remained lower, while at the end of the day in particular he wants to have warmer fruits. Therefore this year he chose to have a more open crop so that the sun can warm the fruits. “By coincidence the good, more open variety Rosheen was available. Breeders are also partners in our trial and follow these developments.”

New Way of Thinking

Many colleagues don’t dare to omit the minimum rail. “That’s a shame because you can save a lot of energy by combining screening with the omission of the rail and still retain quality if you also use a vertical fan. It always used to cost me a lot of effort to save gas. In this way it doesn’t. This is the result of the The New Way of Thinking. We used to look at the appearance of the crop but that was the result of what had already happened and it didn’t tell you anything about tomorrow,’’ he says about the old strategy.

According to advisor Geelen when you have a strategy you can set the course. The temperature- and light sums are in proportion to one another. If you do this consistently you get a balance, rather than always lagging behind the reality. “Therefore this year in the trial greenhouse we deliberately chose to work more with nature in combination with a lower plant burden.”

Production and quality higher


The growers maintain a higher temperature when the radiation is high (5ºC per 1,000 joules) and let the temperature fall at the moment the light decreases. “The grower controls this line every day. The thought is: have more light and a higher temperature so that less ventilation is needed during the day,” says the advisor. As a result, more CO2 and moisture stay in the greenhouse. And that ensures that the light is more effectively converted into assimilates. “The yield and quality rise. The light sum determines the production of assimilates. The temperature determines the consumption of assimilates. On a bright, hot day the sugars that are created are directly converted into production. The crop can then manage better on darker days by having a lower plant burden.”

In the greenhouse the grower shows that there are fewer fruits on the plants. These fruits ripen faster so that on balance the yield is higher. Fruit development is 10 to 15% faster than previously: 18 days instead of 21 days in the trial greenhouse and 21 instead of 24 days in the reference greenhouse. This year he notices that production is rising even faster.

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