Nutrients required for plant growth need to first be dissolved in water - which is why in an aquaculture system those nutrients are far more accessible for absorption by plants. In contrast nutrients in soil are often locked up in aggregates that require bacteria and fungi to break them down and make them available to plants in exchange for the exudates the plants produce to feed them.
Nutrients naturally accumulate in a pond when fish waste and dead organic material decompose. Nitrogen, the nutrient that’s most critical for fish health and plant growth, cycles through the pond with the help of a variety of decomposers.
This results in far more rapid growth of plants in aquaculture systems - where neither water of nutrients act in ways to limit growth. The concept of limiting factor - is a recognition that in nature the availability of some resource will always act to restrict the growth and reproduction of an individual or expansion of a population. In an optimised aquaponic systems many of these limitations are removed - resulting in rapid plant growth. This is further enhanced within the protected environment provided by many aquaponics systems- where plants are often grown in glasshouses and receive nutrients from a high concentration of fish in the water used to irrigate those plants.
On this page we will focus on the optimising the nutrient availability to plants within a closed look aquaponics system - as could be established within a glasshouse connected via a pump to an external fishpond.
Nutrients naturally accumulate in a pond when fish waste and dead organic material decompose. Nitrogen, the nutrient that’s most critical for fish health and plant growth, cycles through the pond with the help of a variety of decomposers.
This results in far more rapid growth of plants in aquaculture systems - where neither water of nutrients act in ways to limit growth. The concept of limiting factor - is a recognition that in nature the availability of some resource will always act to restrict the growth and reproduction of an individual or expansion of a population. In an optimised aquaponic systems many of these limitations are removed - resulting in rapid plant growth. This is further enhanced within the protected environment provided by many aquaponics systems- where plants are often grown in glasshouses and receive nutrients from a high concentration of fish in the water used to irrigate those plants.
On this page we will focus on the optimising the nutrient availability to plants within a closed look aquaponics system - as could be established within a glasshouse connected via a pump to an external fishpond.
Fish Density and Nutrients
In aquaponics, nutrients originate mainly from the fish feed and water inputs in the system. A substantial part of the feed is ingested by the fish and either used for growth and metabolism or excreted as soluble and solid faeces, while the rest of any uneaten feed decays in the tanks. While the soluble excretions are readily available for the plants, the solid faeces need to be mineralised by microorganisms for its nutrient content to be available for plant uptake. It is thus more challenging to control the available nutrient concentrations in aquaponics than in hydroponics. Furthermore, many factors, amongst others pH, temperature and light intensity, influence the nutrient availability and plant uptake. Until today, most studies have focused on the nitrogen and phosphorus cycles. However, to ensure good crop yields, it is necessary to provide the plants with sufficient levels of all key nutrients. It is therefore essential to better understand and control nutrient cycles in aquaponics.
Because in this investigation I focus on the rearing of fish within a natural pond ecosystem and pumping the water from that to the where the plants are (recommend within a glasshouse) the issues associated with fish stock density and changes in pH are not so fragile - as opposed to stocking fish within a restricted tank/container habitat within the glasshouse (as commonly done).
Because in this investigation I focus on the rearing of fish within a natural pond ecosystem and pumping the water from that to the where the plants are (recommend within a glasshouse) the issues associated with fish stock density and changes in pH are not so fragile - as opposed to stocking fish within a restricted tank/container habitat within the glasshouse (as commonly done).
Potential Deficiencies
We also must test pond waters to see what they lack in nutrients and create designs for providing these inputs systemically, as well as adding the components that will convert nutrients into products.
Whether you are just setting up or have a well-established system you’ll need to test the water for a variety of different chemicals. You can do this using a variety of testing kits. Any will do as long as you’re looking at the pH levels, temperature, and electrical conductivity.
These three factors can cause the following issues;
Common Deficiencies
It is useful to know which nutrients are most likely to be missing in your aquaponics. It is worth noting that the type of fish you have and the food you use will affect which nutrients are missing. The basic principle is that the food they need will be supplied by the fish. The most important ingredients in your Aquaponics system are nitrogen, phosphorus, potassium, calcium sulfur, and magnesium. Your plants will also need trace amounts of boron, copper, chloride, zinc, molybdenum, iron and manganese.
Most common deficiencies include:
Adding Nutrients
The method of application depends on the chemical that’s missing:
Whether you are just setting up or have a well-established system you’ll need to test the water for a variety of different chemicals. You can do this using a variety of testing kits. Any will do as long as you’re looking at the pH levels, temperature, and electrical conductivity.
These three factors can cause the following issues;
- Temperature too high or too low: The fish will become stressed and are likely to eat less than they should. This will make them prone to disease and potentially death. It can also cause root disease and slow growth in your plants. In severe cases, you’ll affect the bacteria that convert ammonia to nitrates; destroying your aquaponic system.
- PH Levels Incorrect: Again this will affect the stress levels of your fish causing potential disease issues. Your plants will struggle to absorb the right nutrients resulting in slow growth and, again, bacteria will be killed off preventing the conversion of ammonia to nitrates.
- Electrical Conductivity: This can lead to slow plant growth or exceptionally fast growth. Unfortunately, this will reduce the quality of the crop and the likelihood of bolting.
Common Deficiencies
It is useful to know which nutrients are most likely to be missing in your aquaponics. It is worth noting that the type of fish you have and the food you use will affect which nutrients are missing. The basic principle is that the food they need will be supplied by the fish. The most important ingredients in your Aquaponics system are nitrogen, phosphorus, potassium, calcium sulfur, and magnesium. Your plants will also need trace amounts of boron, copper, chloride, zinc, molybdenum, iron and manganese.
Most common deficiencies include:
- Iron: This is easy to spot by watching your new plants. If they have yellowish growth then the system is low on iron.
- Potassium: Your plants will absorb this soluble element and use it to regulate the processes going on inside the plant. It is also an essential element in the movement of water throughout the plant. You may be surprised to learn that potassium is also responsible for the process that allows gas to enter and leave the plant.
- Calcium: This essential mineral is part of the plant growth cycle. Without it, the structure of the plant is likely to disintegrate as the water cannot be retained properly. Levels of calcium can be affected by excess magnesium or potassium. When the humidity is high and there is little ventilation your plants may also struggle with calcium even if there is enough in the water. You’ll notice they are not losing water and very little is being taken in by them.
- Phosphorus: A lack of this mineral will cause stunted growth in your plants; especially in the early stages of plant development. The leaves may become darker and even taken on a reddish or purple hue. More worrying is the fact that a phosphorus deficiency is likely to prevent your plant from flowering or even growing fruit or vegetable.
Adding Nutrients
The method of application depends on the chemical that’s missing:
- Potassium: There are two main ways in which to add potassium to your aquaponics system: SprayUse potassium chloride and spray it onto the plants. This is a process that you’ll need to repeat at least weekly.Food AdditiveThe alternative is to add potassium in the food through kelp meal concentrate. Other options include potassium sulfate or potassium hydroxide. Unfortunately, there is a complication with potassium. The potassium you add is not always available to your plants. Potassium is known to interact with calcium and magnesium; reducing the amount available to your plants. Therefore to ensure the potassium you supply is used effectively you need to measure the calcium and magnesium levels in your system and ensure they remain balanced.
- Calcium: The most effective way to treat calcium deficiency is via a spray. Simply get calcium chloride and mix it with some water. A good starting ratio is 4 teaspoons per gallon of water. You can always increase the dose if necessary. Then simply spray once a week. You can also add some shellfish bones to your fish tank; this will also increase the supply of calcium and phosphorous.
- Iron: You need to add a form of iron that can be absorbed by the plant. This means using chelated iron; the best one to choose is Fe-DTPA. This will be effective providing your pH is 7.5 or lower; which it should be for healthy plants. You need to aim for 2mg/liter. Simply calculate the size of your water tank and then add the corresponding amount of iron every 3 -4 weeks.
- Phosphorous: This is another essential mineral for healthy plant growth. Again you’ll need to add it in a form that your plants can easily absorb; this will ensure the maximum benefit to your plants. One of the most common and easiest options is to use rock phosphate. You should be able to pick this up at your local garden center. The supplement can be added directly to your plant beds; this will allow the roots to absorb it almost instantly. Ideally, the bed should be shaded from direct sunlight to help ensure it doesn’t dissolve before the plant can get it. You should aim for between 20 and 40ppm for each of your plants.
pH of Water
The acidity and alkalinity should be monitored (lower than 3.7 or higher than 10.5 and fish will die), and these levels can be adjusted with dolomite and oyster shell helping to raise pH levels or peat helping to lower them. Shallow waters will produce a lot of soil, but the excess waste material should be removed before it creates problems.
Acidity and alkalinity should be monitored (lower than 3.7 or higher than 10.5 and fish will die), and these levels can be adjusted with dolomite and oyster shell helping to raise pH levels or peat helping to lower them. Shallow waters will produce a lot of soil, but the excess waste material should be removed before it creates problems.
Acidity and alkalinity should be monitored (lower than 3.7 or higher than 10.5 and fish will die), and these levels can be adjusted with dolomite and oyster shell helping to raise pH levels or peat helping to lower them. Shallow waters will produce a lot of soil, but the excess waste material should be removed before it creates problems.