The Hydroponic / Aeroponic / Aquaponic – Vertical Farming Debate

Definitions:

Hydroponics refers to a system where crops are grown with their roots exposed directly to a nutrient-rich water solution, either permanently (raft systems) or periodically (ebb and flow systems), either without any growth medium, or with the use of an inert medium, such as rock wool, coconut fibre, perlite, gravel, or expanded clay).

Aeroponics utilises a similar nutrient-rich water solution, but this is sprayed onto roots and lower stems, or aerosolised in a high-humidity environment.

Aquaponics combines hydroponics with aquaculture (usually focused upon fish that can be reared for food). In an aquaponics system the fish produces ammonia rich waste, much of which is converted to nitrate and nitrite by bacteria. The nutrient rich water is used to feed plants, and the plants, in turn, help clean the water for the fish.

Vertical farming generally refers to a stacked growing systems, with crops grown not only in rows on one level but in layers, each above the last. These are often housed indoors in a controlled environment. Many hydroponic, aeroponic and aquaponic systems utilise this vertical growing arrangement.

Analysis:

Hydroponic, aeroponic or aquaponic systems provide us with a way to produce food without relying upon soil and with lower overall water requirements than traditionally grown crops. This is immensely useful in regions that are prone to drought or have very poor soils. Many are also housed indoors, in a carefully controlled environment, which makes it possible to extend the range of crops grown, particularly in harsh or adverse growing environments. When these systems are combined with vertical farming, they can also produce significantly more food per acre. Because sunlight cannot reach all parts of a densely-packed vertical farm, however, they are often designed to rely heavily upon artificial lighting.

As all “ponic” systems are soil-less, they are obviously unable to contribute directly to one of Regenerative Agriculture’s most well-advertised aims, soil restoration and soil carbon capture – although some produce biomass as a by-product, which could be used as an input for systems that do restore soil. Long term soil carbon capture requires a plants and microorganisms to work symbiotically and without soil this is impossible.

The intensive but sterile industrial conditions also mean that most cannot contribute to increasing biodiversity. Large operations typically rely upon heavy inputs of synthetic fertilizer, produced through ecologically damaging and fossil fuel intensive processes – the one upside being that they do not leach into the surrounding environment as easily as those applied to fields because of the more tightly controlled growing environment.

As many such operations are driven by purely economic interests, as soil biologist Christine Jones puts it:

“In a hydroponics system you can grow more, larger, leafier vegetables the more nitrate you add. If you’re making money selling hydroponic vegetables you are of course going to put heaps of nitrate in the solution. Much better to consume antioxidant, bioflavonoid, phytochemical rich fruit and veg grown in diverse plant communities in biologically active soil. In a natural soil system, there’s a great deal of two-way communication between roots and soil microbes. Ideally, we want plant roots and the soil to behave as a host with microorganisms. This can’t happen when the roots are in water, being passively fertilised with whatever humans think is appropriate. Also, it is impossible to have mycorrhizal fungi in the liquid medium whether its hydroponics or even aquaponics which is organic. That has consequences for mineral delivery to the food plant and therefore consequences for human health.”

Indeed, nitrates are controversial, as a high nitrate intake has been associated with a number of health issues. However, the growing consensus is that negative health impacts of dietary nitrates from vegetable sources, only exist for vulnerable populations – e.g., very young children or those who don’t receive enough Vitamin C from their diet. In most other populations there are now thought to be a number of health benefits to a diet that includes a lot of high-nitrate vegetables. However, it is theoretically possibly for leafy vegetables in particular to absorb higher amounts of nitrate when heavily fertilised than they ordinarily would. If they were also lower in other complex phytochemicals, such as polyphenols and antioxidants, due to being grown with an improperly balanced feed, this could reduce the health benefits and reintroduce some of the risks.

The produce these systems turn out can be a valuable source of fresh food, particularly when they are integrated into communities where this is in scarce supply. However, as mentioned, fruit, vegetable and salad crops grown in these soil-less systems are not generally as nutritious as those grown in healthy soil. One reason for this is that, they aren’t always given as full an array of nutrients as would be available to them if they were grown under field conditions – sometimes they only receive in the range of 8 – 12 of the most essential ones. When this is the case, there may be many things that people need that will not be in their food – trace elements such as selenium and iodine are classic examples. Humans do not thrive if deprived of these essential elements, and if we’re not getting them from our food, we need to take supplements which are not always easily assimilated.

Perhaps the biggest problem with the current model for most hydro-, aero- and aqua-ponic systems is that many of those investing in them are still operating within the typically industrial paradigm, that prioritises economic considerations over all others. It is this that has helped to normalise systems that require a lot of energy and man-made material (often plastics) to create systems that have high ongoing energy demands and require significant inputs, that are then sourced with very little thought for sustainability, let alone building soil.

There is no reason why such systems cannot find a place in a regenerative food system but to do so they must break with the prevailing industry model. A few examples of steps that could be taken in this direction are included below:

reducing reliance upon synthetic fertilizers and look to existing waste-streams to source chemically and biologically complex organic liquid fertilizers.
giving more thought to the materials used in their construction,
giving more thought to the way they are designed, so that their energy requirements can be, in the first instance, reduced or satisfied passively and in the second, met in a more sustainable way.
moving away from sprawling industrial complexes to smaller, family-run operations, integrated into their local communities.
escaping the bubble of a controlled environment and focusing instead on growing a more diverse range of crops and integrating with their wider surroundings so they can start to play a role in increasing local biodiversity.
Ensuring that inedible biomass produced as a waste product is used productively, or moved along the supply chain to somewhere where it can be so used.

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The Hydroponic / Aeroponic / Aquaponic – Vertical Farming Debate