Aquaponics can help maximize crop yield, while protecting the environment on the other hand. We explain the different types of aquaponic systems, both, for commercial purposes and home gardens.
Did You Know?
A head of lettuce can be grown at twice to thrice its ordinary speed using aquaponics.
Aquaponics is a system which combines fish farming with crop cultivation. Normally, when aquatic animals like fish or crabs are reared in a tank, they excrete ammonia as waste, which makes the water toxic, and has to be removed. On the other hand, when plants like herbs or vegetables are cultivated, they require nitrates to produce a good harvest. So, if ammonia produced by the fish is somehow converted to nitrates, then this is a suitable fertilizer for the crops. On the other hand, water free of ammonia is ideal to be returned to the fish tank.
So, aquaponics can result in a good harvest of both, fish and crops, that too at a much lesser cost, besides promoting the recycling of waste, which is good for the environment. This is made possible by growing plants in a non-soil medium, such as gravel, clay, or simply water, which allows the growth of beneficial bacteria, called nitrifying bacteria. This bacteria converts ammonia from the tank water, first into nitrites, and then into nitrates, which can be absorbed by plants, and is also non-toxic to fish.
There are 3 main techniques by which aquaponics can be implemented, which are given below.
Nutrient Film Technique (NFT)
In this system, water from a fish tank is filtered and passed through the bottom of a horizontal PVC pipe, in a small film. These pipes have holes cut on the top, in which plants are grown in such a way that their roots dangle in the water flowing at the bottom. Nitrogenous wastes from the tank water is absorbed by the plants, and since their roots are only partly submerged, this allows them to be in contact with atmospheric oxygen as well. Purified water is then pumped back to the fish tank. However, since there is no ‘medium’ for the roots to adhere to, this system requires prior filtration to prevent clogs. NFT is only suitable for growing leafy vegetables and herbs which have smaller root systems. Larger fruiting plants like tomatoes require a stable medium to adhere to, and require more nutrients than is provided by tank water.
– Allows the continuous purification of water.
– Partially submerged roots have access to sufficient oxygen.
– Narrow channels or pipes are susceptible to clogging.
– In the event of pump failure or clogs, the roots may be deprived of water, causing loss of crop.
– Not suitable for larger, fruiting plants.
Media-based aquaponic systems, also known as media bed or gravel-bed systems, use a rooting medium like perlite, clay balls, gravel, or river rocks, on which plants are grown. This porous growing bed provides ample spaces for the growth of beneficial, nitrifying bacteria, and also allows for the cultivation of larger flowering and fruiting plants like tomatoes or cucumbers, as compared to NFT or Raft systems. Depending on the arrangement, water may flow at a constant rate through the bed, or the bed may be flooded at times, and dry at others. While the plant roots take up all the nutrients from the water, the gravel bed also has a filtering action, which makes a separate filtration unit unnecessary. Purified water is then routed back to the tank.
– Simple system and relatively inexpensive.
– Similar to ordinary gardening, because the media bed resembles a regular soil bed.
– Suitable for all kinds of plants, from leafy greens to larger fruiting ones.
– The medium performs a filtering action, preventing debris from returning to the tank.
– Trapped waste gradually reaches tray bottom, in a thorough purification process.
– Air is present between medium particles, supplying oxygen to the roots.
– Red worms can be added to the gravel bed for further breakdown of waste.
– Suitable for hobby applications and home gardens.
– A good-quality medium can be somewhat expensive.
– Over time, the pore spaces in the medium may get clogged, causing anaerobic conditions that are bad for plants.
– Regular cleanup of growing bed is required.
– Some types of rooting media may change the pH of the water.
– Not suitable for commercial purposes due to lower productivity, labor intensiveness, and difficulty in large-scale implementation.
– Gravel beds are heavy, and need to be placed on the ground, or on specially-constructed strong structures.
Raft/Deep Water Culture
Raft systems, also known as Deep Water Culture (DWC) systems, use a ‘raft’ of polystyrene, which is floating in at least 1-foot deep water, to grow plants. The raft has well-placed holes in which plants are grown in net pots, such that their roots are immersed in the water. This system can either have a raft floating directly in the fish tank, or have water pumped from the tank to a filtration system, and then to channels containing a series of rafts. An aerator provides oxygen to both, water in the tank, and that containing the raft. Since the roots have no medium to adhere to, this system can only be used to grow leafy greens or herbs, and not larger plants. It is the most popular system for commercial purpose, due to the speed and ease of harvest. Large sections of greenhouses are devoted to tanks containing such rafts, and with time, they get pushed to one side, from where mature produce is harvested. Seedlings are sown in holes from the opposite side of the raft. Thus, it operates like a conveyor system.
– It offers high productivity at low labor requirement.
– Roots are exposed to the most nutrients in this method.
– It is the simplest and most economical of all aquaponic systems.
– Allows for efficient use of space, since raft can be placed in the tank itself.
– It is the most popular system for commercial production, but is also suited for home gardens and hobby applications.
– Plants are easier to harvest, since the roots are submerged in water, and not in any medium.
– Allows for higher stocking of fish, as purification occurs continuously.
– Restricted to growing small, leafy greens and herbs like basil.
– Water is lost by evaporation at the gaps between raft edges and the tank it is kept in.
– Filtration is necessary, since the roots are completely immersed.
– Filtration process increases costs, besides requiring regular filter-cleanups.
– If the roots get covered with tank waste, it may be injurious to the plant.
– Roots are susceptible to microbial attacks, or may be consumed by herbivorous fish.
While these aquaponic systems work fine by themselves, they can also be used in combination to maximize the benefits of each type. An example of such a hybrid system is a fish tank connected to a media bed, and then to an NFT pipe. Besides allowing cultivation of tomatoes or cucumbers, the media bed also filters water passing into the NFT pipe, in which lettuce or basil can be grown. This prevents the need for installing and cleaning the filtration equipment for the NFT pipe.