The Importance of Nitrogen Cycle in Aquaponics Gardening

More and more people these days are engaging in aquaponics gardening. Who wouldn’t want to grow their own food anyway? Imagine being able to raise fresh and healthy fish as well as some healthy and delicious crops at the same time.  And not having to worry about excessive water consumption, waste disposal and other concerns found in other food production systems.

In simple terms, aquaponics is the development of a system that allows plants, aquatic animals and (good) bacteria to work together and thrive. These three elements grow and interact in a re-circulating environment that brings together the positive aspects of both hydroponics (growing plants without soil) and aquaculture (growing fish for food).

A lot of hungry people worldwide can be fed with more nutritious food when productive systems can be implemented. Even drought-stricken areas can manage to grow fresh food because the system uses recycled water. There is no need for constant water replacement for both the plants and fish.  Indeed, only a small amount of water is needed to maintain a well-functioning and productive food system.

One of the most important concepts behind aquaponics is the Nitrogen Cycle.

Points to Ponder

  • The Earth’s atmosphere is made up of approximately 78% of nitrogen.
  • All forms of life need nitrogen.
  • The air has a considerable amount of nitrogen (N2). However, it has limited availability for biological use. Most life forms can’t use Nitrogen in that form.
  • Plants need nitrogen which is in the form of nitrate ions, ammonia, or urea.
  • Animals will then get their Nitrogen from plants or from animals that have eaten plants.
  • Ammonia can be taken up by plants through their roots. But, the majority of plants will rely on the form of Nitrogen that has been properly processed by the good bacteria.
  • While ammonia can be utilized by plants, it can actually be toxic to fish.
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How the Aquaponics Cycle Works

The way an aquaponic system works is easy to understand because it is based on the naturally-occurring Nitrogen Cycle:

  1. Once your fishes are fed, they excrete nitrogenous wastes which are then converted by bacteria to Ammonia.
  2. If nothing is done to eliminate such waste products (wastes from the fish and uneaten food that could build up in the tank) or when the level of Ammonia continues to rise, the fishes in the system will die.

Most people do not understand the importance and functions of bacteria in the cycle.

  1. The Nitrosomonas sp. bacteria are the ones that eat ammonia and convert it to nitrite. But nitrites could also become harmful to some extent and can stop the fish from taking up oxygen.
  2. The Nitrobacter sp. bacteria will then eat the nitrite and convert it to nitrate, which serves as potent plant food. With fish, there is nothing to worry because they can tolerate nitrate in a much higher level.
  3. An aquaponics system is said to have ‘cycled’ when it has sufficient numbers of these bacteria that are working efficiently to completely process the Ammonia and Nitrites.
  4. So instead of doing constant water changes, the water will be utilized by the plants and the bacteria will cleanse the remaining water. When this water passes through the hydroponic system, the nitrites are converted by some bacteria into nitrates.
  5. The water is then sent back into the tank or pond–replenished and healthy enough to sustain the fish.
  6. While the plants get watered and nourished, the fish in turn receive clean water. The cycle repeats itself as long as the two systems function together as one efficiently.
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Some Things to Consider

  • A newly-established aquaponic garden will usually take about 4 weeks to cycle at around 20˚C. The ‘cycling’ will take longer in colder water, and the Nitrifying bacteria will not survive in dry conditions or with temperatures higher than 49°C.
  • The bacteria must inhabit a surface for optimum growth. They usually live in the growing media (gravel, sand, synthetic biomedia, etc.) used for the plants.
  • To monitor the progress of the two essential types of bacteria, test the water for ammonia, nitrites, nitrates and pH with a typical aquarium test kit.
  • The optimum pH range for Nitrosomonas is 7.8 – 8.0 while the ideal range for Nitrobacter is 7.3 – 7.5

Aquaponic gardening can be an alternative food production or farming method. It can be done on a small scale as a means to produce your own healthier and pesticide-free food or on a large scale as a sustainable source of revenue. Just be very patient when cycling your system, and let nature sort things out. Do consistent tests and monitoring (at least daily).  Perform water changes as required and everything will do just fine.

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