Author: Brandon Yep
Degrading soils, nutrient run-off, pesticide-resistance, droughts and increasing fertilizer prices... sound familiar? Conventional agriculture is plagued by several different challenges. While agriculture researchers are working hard to overcome these challenges by creating genetically superior field crops and novel pesticides, alternative methods of agriculture are often overlooked as possible solutions. One of these overlooked methods of agriculture, is aquaponics – the use of aquaculture effluent (fish waste) to fertilize plants hydroponically and the use of plants to filter water for re-use in aquaculture. While a seemingly simple concept, aquaponics has immense potential to increase nutrient-use efficiency which is arguably inefficient in stand-alone aquaculture and hydroponic systems. For example:
Aquaculture is the fastest growing sector in the agriculture industry and is estimated to supply 62% of the 146 million metric tons of global fish supply, predicted to be demanded by 2030(1). With traditional aquaculture systems only capturing 25% of nitrogen in fish(2), there is an immense opportunity for plants to recapture nitrogen and other nutrients.
Aquaponics mitigating nitrogen pollution in aquatic environments.
Simultaneously, hydroponic operations require high quantities of mineral fertilizer which require substantial energy to produce. For example, the Haber-Bosch process (the production of nitrogen fertilizer from nitrogen gases in our environment) has been previously attributed to 57% of the total energy costs associated with agriculture(3). Furthermore, phosphorous fertilizer or phosphate rock is a finite resource that has been estimated to be half depleted in the next 60 to 70 years from over mining(4).
Although largely ignored as a commercial solution for fish and plant production, a resurgence in aquaponic research and commercial operations has grown exponentially in the past 5 years over concerns of agriculture’s impact on the environment(5). However, if aquaponics is to be a legitimate replacement for plant production, it must be optimized for crop production during the flowering stage, as many food and medicinal crops are grown during flowering (e.g., tomatoes, cucumbers, cannabis). Currently, flowering crops are more difficult to grow in aquaponic systems due to their higher nutrient requirements.
My thesis-research has used cannabis as a model crop to determine what nutrients may be limiting in aquaponics for flowering crops and how it can be improved, so that cultivators can produce competitive yields to hydroponics while using less. My research has found that aquaponic cultivators can supplement potassium and micronutrients (e.g., manganese, iron, etc.) into their solution to improve plant yield(6), as these are often in low concentrations in fish feed. More broadly, my research has demonstrated that natural state of aquaponic solution (i.e., organic particles and beneficial plant microorganisms) may allow aquaponic plants to be more tolerant of salt stress(7) and nutrient deficiencies.
What this demonstrates is that aquaponics can be a legitimate commercial producer of plants and may be more tolerant of stressful conditions applied in hydroponic solution.
References
(1) Food and Agriculture Organization of the United Nations, 2016. State of world fisheries and aquaculture. Rome. https://doi.org/10.5860/CHOICE.50-5350
(2) Hargreaves, J.A., 1998. Nitrogen biogeochemistry of aquaculture ponds. Aquaculture 166, 181–212. https://doi.org/10.1016/S0044-8486(98)00298-1
(3) Mudahar, M.S., Hignett, T.P., 1985. Energy efficiency in nitrogen fertilizer production. Energy Agric. 4, 159–177. https://doi.org/10.1016/0167-5826(85)90014-2
(4) Oelkers, E.H., Valsami-Jones, E., 2008. Phosphate mineral reactivity and global sustainability. Elements 4, 83–87.
(5) Yep, B., Zheng, Y., 2019. Aquaponic trends and challenges – A Review. J. Clean. Prod. 228, 1586–1599. https://doi.org/10.1016/j.jclepro.2019.04.290
(6) Yep, B., and Zheng, Y. (2020). Potassium and micronutrients addition in aquaponic solution for drug-type Cannabis sativa L. cultivation. Manuscript under review in Canadian Journal of Plant Science.
(7) Yep, B., Gale, N.V., and Zheng, Y. (2020). Aquaponic and hydroponic solutions modulate NaCl induced stress in drug-type Cannabis sativa L. Manuscript under review in Frontiers in Plant Science.