In the last post, I introduced you to the fundamental ways in which vertical farms are structured – from small home and business farms using vertical pipes or A-frames, to larger scale enterprises using stacked plant beds or the designs of the future – the multi-story production powerhouses. What all of these vertical farms have very little of, if at all, is soil. So how do they grow these plants? What technologies drive this soil-less production.
The first of these technologies is Aeroponics. The name is derived from Greek, aer meaning air, and ponos meaning labour. The plants are grown without a growing medium – the roots hang in the open air. The nutrients are delivered via a fine mist that the roots then absorb. A lot of the vertical pipe based growing systems used Aeroponics as the nutrient delivery system of choice. Aeroponic systems benefit from:
- High concentrations of Oxygen in the root zone of the plant, also known as the rhizosphere, which is needed for growing healthy plants. An Aeroponics system can deliver more oxygen to the growing plants compared to a traditional or alternative growing medium.
- Aeroponics systems can also limit the spread of plant based diseases because there isn’t a medium through which the disease can spread.
- Aeroponics systems also have very efficient water consumption – much like a shower is more efficient than a bath, so to is Aeroponics compared to other farming methods.
- Aeroponics systems will often be ‘closed loop’ as well, meaning that the mist that isn’t absorbed by the plants is captured as it condensates and is recycled back into the system.
The next technology is Hydroponics – these are plants that are grown in either a nutrient rich water solution or an inert medium like gravel through which the nutrient water is run. Hydroponics is a method often used in the stacked horizontal growing beds. Hydroponics benefit from:
- Balanced growing conditions where the nutrient solution can be PH adjusted and well circulated to make growing conditions as ideal as possible.
- The water based delivery allows the plants to absorb nutrients with very little efforts, compared to soil grown plants where the roots need to seek out water and nutrients. In the Hydroponics system, the energy that isn’t spent on growing extensive root systems goes instead into the plant’s growth.
- The boosted plant growth means that Hydroponically grown plants grow faster, they grow more and have greater yields compared to a soil grown equivalent.
An issue that Hydroponics systems can suffer from is an issue known as ‘root rot’ which is pretty much how it sounds. This is often down to poorly oxygenated water, water that is too hot or too cold, and water that hasn’t been refreshed and thus there is a nutrient build up. There are several different techniques for implementing Hydroponics systems, some of which mitigate the risk of root rot better than others, as well as having different levels of affordability. These techniques include:
- Drip System: An irrigation array drips water onto the plants which work its way through the inert medium providing the plants with a gentle flow of water.
- Wick System: Wicks passively move water from a reservoir into the inert medium where the plants can access it. Plant growth is slower but a wick system is low maintenance and cheap.
- Deep Water Culture System: The plant roots sit in the water reservoir, which is a simple and reliable method however it is more prone to root rot than other systems if not maintained.
- Ebb & Flow System: These systems flood the growing tray then let it drain before flooding it again, continuously cycling over the plant’s growth.
- Nutrient-Film System: This system uses a slanted growing tray, where the water is pumped into the high end and allowed to trickle down the growing tray before draining back out at the low end.
Finally, we get to Aquaponics, which can be implemented using the same systems as described for Hydroponics, however instead of the nutrients in the water being added by the farmer, they instead come from an animal of some description. The term, in fact, is a cross between Aquaculture, which is the practice of farming aquatic animals in tanks, and Hydroponics, which as we know is growing plants without soil.
An Aquaponics systems work by having a rearing tank where the animals are raised. The animals produce ammonia rich waste, which increases the ammonia levels in the water. The waste water is taken from the rearing tank into a secondary tank where nitrification bacteria convert the ammonia into nitrites and then into nitrates, which is the form usable by the plants. This nitrate rich water is now pumped into the plant beds, using one of the Hydroponic methods, or Aeroponics. The recaptured, low nitrate water is then pumped back into the rearing tanks as clean, aerated water. This is an important step because if the water that the animals are being grown in is too high in ammonia, it becomes toxic to the livestock. You can see a simplified version of this in the image below.
The beauty of an Aquaponics system is that the animals feed the plants and the plants filter the water for the animals. Not only is this an efficient production system, benefiting both the animals and the plants. It also gives the farmer two sets of produce! Fish are a common animal to use in Aquaponics systems, the most commonly used species being:
- Tilapia, ready for harvest anywhere from 6 to 9 months
- Trout, ready for harvest anywhere from 12 to 16 months
- Perch, ready for harvest anywhere from 9 to 16 months
- Catfish, ready for harvest anywhere from 5 to 10 months
- Barramundi, ready for harvest in 12 months
- Bass, ready for harvest anywhere from 12 to 18 months
Other water-based livestock includes Shrimp, Crayfish and Lobsters. Alternative nutrient sources can also come from Ducks and Worms.
Want to learn more about the technologies discussed here today? Take a look at these links!