As you know, all living organisms need specific nutritional elements to live and prosper.
But, plants will be happy and give us high yields only if we know what they need, whether we grow them in aquaponic system or by traditional farming methods.
Aquaponics system produces many nutritional elements that are essential for plants growth and development.
But, as with any other growing method, you need to know what your plants need and to closely monitor levels of important nutrients so that you can react on time if you notice any nutrient deficiencies or abundance.
This article covers all important facts about non-mineral, macro- and micronutrients in aquaponics. I’ve also covered some techniques I use to overcome most common nutrient challenges in aquaponics.
Nutrients in aquaponics
The primary source of plant nutrient in an aquaponics system is the fish food.
But, it should be noted that in contrast to plants, fish nutrition is very different and the composition of fish feeds depends mainly on the type of the fish.
Typically, fish feed contains an energy source (carbohydrates and/or lipids), essential amino acids, vitamins, as well as other organic molecules that are necessary for normal metabolism but that fish cells cannot synthesize, and other macro- and microminerals.
For this reason, it is important to choose a good quality fish food for your fish.
Fish can not magically produce a full range of plant nutrients from a poor food inputs. So, it’s quite logical that a good quality, balanced fish food will serve the overall aquaponics system very well.
Nutrient deficiencies in fish are often accompanied by disturbances in the balance of other minerals. More on this you can find in my previous article on how to create great aquaculture environment in aquaponic systems.
Another good way to provide all the micronutrients the plants require is to make sure you have incorporated grow media beds into the system. Grow media beds provide a wonderful environment for the development of nutritional elements.
Over time fine solids will build up in your grow beds and the worms will take up residence, or you’ll add them to grow media. The worms will move through the media bed and process the solids collected there. The solids are reduced in volume and locked up nutrients will be released.
In general there are three types of nutrients that we need to pay attention to when growing food in aquaponic system:
- Non-mineral nutrients: Oxygen (O), Hydrogen (H) and Carbon (C)
- Macronutrients: Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulfur (S)
- Micronutrients: Iron (Fe), Copper (Cu), Zinc (Zn), Manganese (Mn), Boron (B), Molybdenum (Mo), Chloride (Cl)
Usually, in aquaponics, with appropriate fish stocking rates the levels of nitrate and nitrite are sufficient for good plant growth. But, phosphorus, calcium and iron could be limiting.
The necessity to add nutrients to the aquaponic system depends mainly on the growth stage of the plants.
Provided that the system is stocked with enough fish, it is not necessary to add nutrients for plants with short cropping cycle, which does not produce fruits (e.g. salads).
In contrast to, for example, lettuce, tomatoes that needs to bear fruit, mature and ripen, need supplemental nutrients.
Non-mineral nutrients in aquaponic system
Non-mineral nutrients are essential for growth and development of plants.
In aquaponic systems oxygen is delivered to plants through water.
But, for oxygen to be available in sufficient quantities we need to add it to water with oxygen sprayers or by creating waterfalls. This will enrich water with dissolved oxygen that plants need.
On the other hand, in aquaponic systems fish creates carbon dioxide during the night and since the plants absorb carbon dioxide during sunrise and in morning hours we usually don’t have to worry about it in aquaponics.
Macro and micronutrients in aquaponic system
The power of aquaponics is in ammonia circulation and nitrification bacteria.
Microbial communities (consisting of bacteria located in the bio filter and in the grow medium) play major roles in the nutrient dynamics in aquaponic systems.
Their primary role is to convert ammonia to virtually non-toxic nitrate but they also contribute to the processing of particulate matter and dissolved waste in the system.
Both functions are absolutely crucial for the stability of an aquaponic system. This process is also reducing water pH level and this is very significant in aquaponics.
pH level is important because some nutritional elements are only available at higher pH values, but more are only available at low pH values. This can make the lives of aquaponic growers pretty difficult at times.
Nutritional material gets into aquaponic system as organic particles. As we add fish food to the system this food is creating organic particles regardless of the fact whether the fish is eating it or not.
Organic particles are transformed into organic nutrient elements that are not attached to organic molecule and for this reason we are calling them non-organic elements.
These are nitrogen, phosphorus, potassium ion, chloride ion, zinc ion etc. All these elements become non-organic nutritional elements in aquaponic system.
Sometimes these elements can be microbes or other organisms but they all oxidize and become non-organic nutrients that our plants will love.
Calcium and magnesium are most commonly supplemented in aquaponic systems that use pH-raising supplements to moderate pH level. Primarily calcium and magnesium in the form of agricultural lime or hydroxide composed of Ca and Mg.
It isn’t necessary to supplement sulfur in most systems. But, it is commonly supplemented in neutral or high pH system if growers use Epsom salts (magnesium sulfate) or potassium sulfate.
When talking about micronutrients:
- Copper is usually included at high levels in the fish food
- Zinc is also common in fish feed as well as the galvanized steel components that inevitably make their way into our systems.
- Boron is required at low levels and most aquaponic systems have sufficient amount of it
- Molybdenum is also required at low levels, to the extent that all of the molybdenum a plant needs for its entire life can often be found in the seed that it germinated from
- Manganese is seldom deficient
- Chloride commonly enters the system with the fish food, and in the form of salts
Nutrients availability in aquaponic system
What is important to note is that not all elements that we add to the aquaponic system will be available for plants.
One part of nutritional elements is lost as it leaves the system before plants absorb them.
The other part of nutritional elements is lost due to absorption of nutrition by other aquaponic system elements but not plants. For example, as we have algae in our aquaponic system, they can die and be eaten by worms in which case the worm has absorbed nutritional elements.
Third part of nutritional elements that don’t find the way to the plants is the part of elements that is available in the system itself but not available for plants.
Basically this means that instead of being dissolved in the water in the system, the nutrient becomes a solid and usually settles on the bottom of the tank, or attaches to a piece of gravel, or other surface in your system.
This means that while the nutrient is technically there, it’s not available for the plant to take up. These can be salts and other elements that we add to the system in wrong forms.
The best example of this is iron. Iron is often present in aquaponic systems, however, because of system pH and dissolved oxygen, it typically isn’t very available to the plants. That’s why iron deficiencies are common problem in aquaponics.
To overcome this challenge we need to closely monitor iron levels in water. The best way to boost iron levels in aquaponic system is by adding iron chelate once in every three weeks. Ideal level is 2 ppm so you need to calculate the amount of iron chelate you need to add to the aquaponic system and this mainly depends on the quantity of water in the system.
To satisfy all micro and macro nutritional needs it is important to have in mind that some nutrients are added to the system in specific form in order to make other elements available to the plants.
For example, to achieve targeted pH level, I am usually adding potassium hydroxide [KOH] or calcium hydroxide [Ca(OH)2] to the system.
These compounds are the best because they do not increase sodium salts in the system, which is toxic for the plants and can cause many problems.
As I mentioned above, potassium and calcium are essential macronutrients for healthy plant development (especially for plants without fruits like salads). So by adding potassium hydroxide and calcium hydroxide to the system we are also boosting potassium and calcium levels.