Aquaponics is a system of cultivation that is starting to become much better known, both in terms of commercial agricultural production and the smaller scale of the permaculture gardener. It is appealing to both because it is a system that requires very little input in order to function well, and produces two types of food product – plants and fish.
Aquaponics uses a linked system of fish tanks and vegetables beds. The only inputs needed are food for the fish and a method to pump water around the system (gravity can be used one way in some circumstances, but even then a pump will be required to complete the cycle). The basic system involves pumping the water from the fish tank, complete with the droppings of the fish, into the vegetable beds. The plants use the nutrients from the droppings that are in the water, and in doing so filter the water so that it is clean enough to go back into the fish tank. There are three major forms of aquaponics systems
The media bed aquaponics system is probably the easiest to set up on your permaculture plot. It consists of garden beds filled with small porous rocks – typically clay pellets – into which the vegetables are planted (this is a no soil system). Water from the fish tank is either pumped or drained via gravity, depending on the specifics of your site, into the beds so that the plants can access the nutrients. The rocks are porous to allow them to hold water for longer for more efficient nutrient uptake, and to remain aerated. The rocks also serve to filter out biological organisms such as parasites to prevent them going back into the fishes’ water, as well as any solid material (plants take up nutrients in a dissolved, soluble form, so any solids would not be used and hence contaminate the water if they returned to the fish tank). The clean water drains into a container below the garden bed, and is then pumped back into the fish tank.
The garden bed can either have a continuous flow of water moving through it or is alternately flooded and drained, using a siphon to drain the water when it reaches saturation point. The media bed system can be used on a small or large scale and provides good plant support. The major disadvantage is that the rocks used to fill the beds can be quite and expensive initial cost. Permaculture gardeners choosing this system must also keep an eye on the pumps so that they don’t get blocked with fish waste, and ensure that with either the continuous flow or ebb and flow systems, no part of the garden bed becomes waterlogged, as this can cause it to become anaerobic and affect plant growth.
Nutrient Film Technique
The nutrient film technique involves siting a series of pipes adjacent to the fish tank and pumping water through them as a very thin film. The water moves slowly allowing plants, which have been placed in holes in the pipe, to access the nutrients within. When the water reaches the end of the pipes, it is pumped back to the fish tank. Because there is no solid material or surface of the water open to the air, extra filtration equipment is needed to clear the water of solid and biological waste before it is returned. However, the system is very efficient in its water use.
This system is probably best used in large-scale aquaponics system, and has the disadvantage of being unable to support larger, heavy plants, such as tomatoes and cucumbers, which can be utilized in the media bed system. It is primarily used to cultivate leafy greens and salad greens, which have small root systems and are relatively lightweight.
Deep Water Culture
The deep-water culture system is sometimes referred to as the deep flow system, and involves siting the plants on rafts through which their roots protrude and hang in the nutrient-rich water from the fish tank. The water must be filtered of any solid waste before reaching the plants, but aside from that, the equipment required is minimal and can be sourced cheaply. While commercial operations often use specially constructed channels to hold many rafts (allowing for ease of harvest, as well as capacity for higher yields) the system can easily be used in permaculture gardens. Simply punch holes in the base of a Styrofoam container, plant your crop through them, and float on the surface of the fish tank, with the filtrations system attached. Just ensure you stock your tank with fish species that are not voracious plant eaters, so they do not decimate the roots.
This system has the advantage of a more stable environment for both the plants and the fish. Because the water is not moved from the fish tank into other systems, it does not experience fluctuations in pH or temperature.
Whichever system you use, there are many fish species that you can choose to stock your aquaponics system with, from catfish and tilapia to carp and crustaceans. Set up costs can be minimized by using recycled containers for your fish tank (making sure they are thoroughly cleaned before stocking) and garden beds. You will also need to ensure that the water is oxygenated. Because a fish tank is a static body of water, it needs a pump to force air into it and provide the fish with sufficient oxygen. When sourcing food for your fish, try to ensure that it comes from an organic sustainable source. One of the major pressures on wild fish stocks is the use of small fish to make fish food for captive stocks. This not only throws wild ecosystems off balance, but it is an inefficient use of resources, with several grams of fish needed to make just one of fish food. Some enterprising permaculturists have combined livestock resources by sting their chicken coop above their fish tank, so the chickens’ dropping provide food for the fish, and the gardener only needs expend time and energy on the harvesting!