Nutrients in controlled environment agriculture (CEA) are combined with water as a fertigation solution, and can be generally described as being either ‘flood-to-waste’ or ‘recirculating’ in nature. We often think of recirculating fertigation systems in CEA as being circular, yet all discharge a proportion of nutrients and water (typically 30% every two weeks) in order to prevent plant root exudates (organic chemicals) and certain inorganic chemicals (e.g. ammonia or nitrites) building up to potentially toxic levels for plant growth. Beyond this, innovations in circularity within the production system tend to focus on water use, and either focus on preventing excess evapotranspiration by using low-heat electrical components and through system design, or focus on capturing moisture from the air by using condensation tubes, cold walls or dehumidification.

Very few innovations, aeroponic spray delivery and the aeration of hydroponic media excepted, directly target nutrient uptake and use efficiency within hydroponic systems, with even fewer targeting the circularity of nutrient inputs and outputs within CEA systems. In general, CEA fertigation solutions are as concentrated as they can be, as they need to provide guaranteed nutrition both spatially and temporally. Furthermore, they typically utilise inorganic nutrients from unsustainable sources (i.e. rock phosphorus and energy-intensive, electrochemical nitrogen reduction) and CEA discharge waters, although deplete of certain nutrients, are typically still nutrient-loading to a receiving water.

With this in mind, and considering the diffuse pollution conundrum within UK field-based agriculture, the recent upturn in local-level anaerobic digestion, and the advent of novel algal bioreactor technologies, for example, one can begin to sketch out an opportunity for these technologies and production systems to integrate at the systems level to address nutrient circularity challenges. The flow diagram (upper left) outlines a basic, conceptual nutrient flow diagram that could work towards circularity by:

• Harnessing diffuse pollution from raw drinking water and turning this into a recycled feedstock for liquid fertigation (via CEA crop production and via liquid fertilizer production for field crop production)
• Harnessing the discharge nutrient solution from CEA systems for algal growth for biofertilization within both CEA and in-field crop production
• Interlinking crop waste, algal biomass, and excess nutrients from water purification via anaerobic digestion technology and ad-mixture innovation, in order to feed regenerative agriculture and promote soil health.

We are already collaborating with an innovative SME in this fascinating innovation area and this will be one of the several ideas that CHAP will be pitching at the ISCF ‘Future Food Production Systems’ consortia-building event in Birmingham on Wednesday 23^rd October. Please get in touch if this idea is of interest to you, or grab us at the event if you are signed up to attend.

If you have any other questions specifically about our Controlled Environment Agriculture capabilities, please send us an email at enquiries@chap-solutions.co.uk

Please note, the opinions expressed in this article are the author’s own and do not necessarily reflect the views or opinions of CHAP.