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Circular Nitrogen as Fertiliser for Greenhouse Horticulture
Exploring new ways to utilise nitrogen-based fertilisers plays a crucial role in the transition towards a more circular greenhouse horticulture sector. For nitrogen to be used efficiently and safely, the nutrient must be both pure and highly soluble. Alexander van Tuyll from Wageningen University & Research’s Business Unit Greenhouse Horticulture (WUR) highlights the possibilities for using circular nitrogen from residual streams and green alternatives to conventional chemical processes.
Plants require nitrogen to grow. Although the air around us consists of 78% nitrogen, its natural form—N2—is not directly available to plants, explains researcher Alexander van Tuyll. “In order to use atmospheric nitrogen as a nutrient, the nitrogen atoms must first be split. Since these atoms are very tightly bonded, breaking them apart requires a great deal of energy. The most common method for doing this is the Haber-Bosch process, but this process relies heavily on natural gas. Natural gas is associated with CO2 emissions and frequent price fluctuations, which is why we are keen to move away from it.”
A project in collaboration with the Club of 100
There are various alternatives for nitrogen fertilisation, such as extracting nitrogen from the air without using natural gas, or reusing nitrogen from residual streams. Both of these routes are the focus of a joint project between WUR and the Club of 100. Van Tuyll explains: “For example, in the Haber-Bosch process, green hydrogen could be used instead of natural gas. When it comes to residual streams, nitrogen can be recovered from sources such as wastewater or animal manure. These alternatives are already being explored and applied by several members of the Club of 100. However, the available knowledge is still quite fragmented. Our goal was to present these options in a clear, structured overview within a White Paper, specifically aimed at application in greenhouse horticulture.”
Recovering nitrogen from residual streams
Van Tuyll also highlights the challenges of extracting nitrogen from residual streams:
“For crops grown in recirculating systems, like vegetables, the requirements for fertilisers differ from those in arable farming or ornamental plant production. One key requirement is solubility, so the fertiliser can be delivered efficiently via drip irrigation systems. Another important factor is a low contamination level—the fertiliser must be free of sodium and heavy metals.
To solubilize nitrogen, bioreactors can be used. In a recirculating greenhouse system where drainwater is recaptured, our research found that contamination levels must be much lower than European safety limits – doable, but important to know.
A whitepaper offering clear insights
The researchers also compared energy consumption for the various methods:
“Even when using green hydrogen, the Haber-Bosch process remains far more energy-intensive than extracting nitrogen from residual streams. On the other hand, nitrogen from residual streams tends to have a lower concentration, which can present additional logistical challenges.
With this White Paper, we aim to provide a clear comparison of both approaches. This will allow fertiliser producers to make well-informed decisions and develop their products in the most sustainable way possible. Ultimately, this also helps growers achieve more sustainable cultivation.”
The nitrogen project is a collaboration between the Business Unit Greenhouse Horticulture and Wageningen Food & Biobased Research. Researcher Marc Lanting, representing Food & Biobased Research, investigated the various technologies involved.
This White Paper on nitrogen is the first in a series of three focusing on the use of circular fertilisers in greenhouse horticulture. The upcoming publications will address magnesium and zinc, or another micro-nutrient.
The circular fertiliser project is funded by the collective resources of the Club of 100.