Today we will take a look at various transformations of nitrogen inside the aquaponic system. The cycle of nitrogen is one of basic natural processes and a power to plants' growth.
Nitrogen is a bit shadowed by generally favorite oxygen. Nevertheless, it is actually a nitrogen that creates 80 % of the atmosphere and that can be found in many important compounds such as alkaloids (the most know alkaloid is caffeine).
The molecule N2 is unbelievably stable at standard conditions. This also means great release of energy during burning, exploding or other disintegration of nitrogenous compounds into gaseous N2. This mechanism is used with many explosives, for example well known nitroglycerin.
The nitrogen contained in amino-acids, subsequently in food proteins, is the most important to us. It is exactly this form of nitrogen that enters our aquaponic system through special granulated fish food. Granulated fish food is made from plant meal – cereals, legumes and other food additives are contained to ensure healthy growth of fish.
Predatory animals' granules contain around 45 % of protein while herbivorous carps are well with granules with protein about 25 - 30 %. Fish ability to convert proteins into muscle (meat) differs depending on species. Also the temperature of water affects the metabolism of these cold-blooded animals. However, thanks to long-time breeding the requirements of all commercially bred fish are well mapped and published on the internet.
Fish are without doubt champions among farm animals in the conversion of food. For example rainbow trout reaches up to 1:1 conversion rate in professional farms. This means that his body weight grows by 1 kg for every 1 kg of feeding. For our purposes we will be humbly counting with half of that conversion rate. It means, in general, that half of the nitrogen contained in fish food will be transformed into fish body weight and the other half will be excreted.
The aquaponic system collects the extra nitrogen (in both solid and dissolved form) together with leftovers from fish food and saps them into sump tank where they are held by a set of overflows. This residue is pumped off regularly to avoid its accumulation that could lure colonies of bacteria which can consequently kill the fish.
However, throwing away the paid-for nitrogen would be a waste. Since we want to use the nitrogen as much as possible we have to put it back into the system. We just need to find the right form for its re-entry.
The necessary transformations will be done by earthworms. We will set for them a moist home right next to the outflow from the sludge tank where these little worms will consume the residue from fish tank with occasional chopped green grass, that we will throw them.
If the conditions are ideal, earthworms will double its colony in few weeks. And since fish love earthworms the nitrogen contained in worms will get back into fish stomach in form of fresh protein and there goes another chance for fish to turn our Nitrogen into a fillet.
The same process of reusing the nitrogen works for plants which absorb nitrates. The residue from vegetable goes into compost from where part of the nitrogen (in form earthworms) goes back into the fish stomach.
Coincidentally earthworms creates probably the finest organic fertilizer called vermicompost that can be used elsewhere in the garden. Said strategies are called as extended aquaponic cycles. Fish scavengers (for example catfish) could be fed by remainder of gutted fish. However this form of cannibalism is not ethical and in some countries it is even illegal.
Nevertheless, there could run another extended aquaponic cycle based on supplementary poultry breeding, that can help to solve the ethical problem. For example quail – my favorite. Quails eat earthworms, vegetable and even remainder of fish. One quail can lay up to 300 eggs per year and their meat is delicious too. Remainder of poultry is fed to scavenging catfish and the system starts new nitrogen cycle again and again.
Now, you can understand how efficient system could be created and its essence is very simple: do not try to beat the nature, just replicate what was mastered by millions years of evolution.
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