Water Usage in Zero-Emission Greenhouses

Achieving zero emissions in greenhouses is a big challenge. I’m not just talking about CO2 emissions. Greenhouses emit fertiliser and pesticides into the environment as well (see this article for more background on that). Water is only 2-3% of a grower’s costs, but oxygen is free and we still need that. In the future, zero-emission growing will become a boundary condition for greenhouses in the Netherlands. Because of this, a lot of research is being done.

Of course, research won’t make a difference if it isn’t being applied. It’s great how industry, academia and government work together in the Netherlands to make this easier. Glastuinbouw Nederland and Wageningen University & Research have been giving a few free webinars lately. Almost a month ago, they gave one on water quality and zero-emission growing.

The event was opened by Sjaak van der Tak, president of Glastuinbouw Nederland. He outlined two main goals within irrigation:

  1. Virtually zero emissions (nutrients and plant protection products) by 2027, as agreed in a covenant with the government
  2. Achieving good quality irrigation water (related to many challenges including climate change).

Research Programme

Margreet Schoenmakers, programme manager at Glastuinbouw Nederland, then presented the research programme of Kennis in je Kas (‘know-how in your greenhouse’). KijK is foundation doing a lot of great research, like Kas als Energiebron (‘greenhouse as an energy source’). This webinar focused on Glastuinbouw Waterproof.

Some points she mentioned about Glastuinbouw Waterproof that stuck with me:

  • They are working on making zero emissions possible for as many types of plant protection products as possible. This is crucial, since the more PPPs they manage to find ways to use without emissions, the broader the palette of tools available to the grower. Again – zero-emissions growing will be a boundary condition very soon!
  • Glastuinbouw Waterproof receives half of its funding from the Dutch government and the other half from industry.
  • ‘Almost’ zero-emission growing works for tomatoes and cucumbers in experimental settings. For orchids and phalaenopsis, this is more challenging – but slow-release fertilisers seem to help decrease nutrient emissions. A lot of progress has been made on zero-emissions growing though, so they are moving their focus to other things like circular horticulture.
  • They are working on a cheap and robust nitrate sensor. Instead of having to use nitrogen strips, you could just use their device. This would be like a pH- or EC meter.
  • The faster a crop transpires, the sooner you will have to leach to get rid of excess sodium. This is why Glastuinbouw Waterproof is looking at strategies to counteract transpiration. They are experimenting with lysimeters to develop a virtual lysimeter that can measure water flows, including transpiration.
  • They also want to work on investigating the effect of dissolved oxygen on emissions, but there’s no funding for that at the moment.
  • Lastly, Margreet brought up the idea of a regional water bank using COASTAR (coastal aquifer storage and recovery). This is a buffer that multiple greenhouses could tap into. With ground water availability being worse in recent years, this is increasingly relevant.

Jim van Ruijven from Wageningen Research then went into detail about some of the projects he’s been involved in:


Bacteria are inevitable – even in space, they get into the irrigation system. When bacteria attach to rough surfaces and fertiliser residue, they secrete polysaccharides. This leads to a slimy biofilm, which can lead to blockages and diseases.

Can chemical and/or physical cleaning be done without emissions? In this project, they tried out different strategies and measured the presence of bacteria using these black plastic rings, starting from a clean system. To estimate the amount of bacteria on one of these rings, they measured the presence of ATP. This is a technique used by the military when looking for safe water.

Antibacterial coatings were not found to make much of a difference. Filters did, however. The finer the filter, the better UV penetration was, killing more bacteria. Disinfectants like Oxyl-Pro helped too, especially for prevention, by nipping bacterial growth in the bud.

Ontsmetten van looftrekdoeken groeit in populariteit' - Vakblad Onder Glas

Emissions at crop rotation

A huge amount of emissions happen during crop rotation. Old water gets flushed out, the greenhouse gets cleaned, and so on. Just rinsing the cover, gutters and pipes uses 150 cubic metres of water per hectare (1.5 litres per square metre). Because of the high volumes used in such a short amount of time, reusing and filtering are big challenges. Storage and filter capacity are the bottlenecks.

Emissions are especially high when growers choose to reuse their substrate. Of course, reusing substrate reduces huge amounts of waste – but this does create more emissions when the old substrate gets flushed through.

What solutions does Jim recommend? Firstly, more gradual flushing. Recirculating water is another one. Recirculation can take a while – but despite its costs, having the extra plumbing to recirculate water has advantages for the crop as well. To recirculate, choosing the right plant protection products is important, since some can be recirculated better. Lastly – if you must leach water, then filter it before it leaves the greenhouse.


Jim thinks recovering water from transpiration is a development to keep an eye on. It’s something they brought up at GreenTech as well. He showed a video with a gerbera grower explaining how he uses a product called DryGair to extract water from transpiration. This also helps recover energy.

To look at different strategies, the plan is to combine two models: Kaspro and Waterstromen. Once these are combined, they will simulate different scenarios: allowing a high relative humidity, limiting transpiration, recovering transpired water, and even using hydrogen gas as a source of water.

Closing Remarks

As is often the case with research, this webinar was information-dense. I hope this article was useful. It’s fantastic that these discoveries can be made available so easily in free webinars. Let me know if you’d like to see the slides and I can share them with you.

If you understand Dutch, be sure to put their upcoming webinars in your calendar! On 19 November they’ll be discussing ion-specific sensors and how they can help optimise irrigation, and on 10 December the topic will be about growing with more sodium in the irrigation system.

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