Plant nutrient deficiencies are common even in traditional and other methods of farming. In aquaponics, it is one of the most common problems that aquaponics gardeners deal with. Maintaining the nutrient balance in aquaponics can be frustrating, especially when most of what you read about aquaponics says that fish provides food for the plants in the system.
Plant nutrient deficiencies occur when essential nutrients are not enough or readily available in the fish wastes used to feed the plants. Fish waste is an excellent source of organic nutrients for the plants, but sometimes it is not enough. There are many important crop nutritional considerations that you need to know in the closed recirculating system of aquaponics.
In aquaponics, it is important to recognize, identify, and understand the problem to manage plant nutrient deficiencies.
Nutrients in Aquaponics
Fish food is the primary source of plant nutrients in an aquaponics system. However, in contrast to plants, fish nutrition is very different, and the composition of fish feeds depends on the fish type. Usually, the fish feed contains carbohydrates, essential amino acids, vitamins, and lipids (an energy source), and other organic ingredients necessary for the fish’s healthy growth. Fish cannot produce a full range of plant nutrients from unbalanced fish feeds. That is why it is essential to choose a good quality fish feed for the fish in aquaponics.
We need to pay attention to three types of nutrients in growing plants in the aquaponics system.
- Macronutrients: Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulphur (S)
- Micronutrients: iron (Fe), Copper (Cu), Zinc (Zn), Manganese (Mn), Boron (B), Molybdenum (Mo), and Chloride (Cl)
- Non-mineral nutrients: Oxygen (O), Hydrogen (H), and Carbon (C)
Macronutrients In Aquaponics
Most plants require a combination of the same basic macronutrients and micronutrients. Macronutrients are the nutrients required at high concentrations, while the micronutrients are only required in trace amounts.
The most supplemented nutrients via fertilizers in traditional farming are nitrogen, phosphorus, and potassium or NPK in fertilizer solutions. These are the essential macronutrients that are important in plant growth.
Most macronutrients are readily available in an aquaponics system, but its concentration depends on the fish’s fish food. Nutrient supplementation happens when the macronutrients in the system are not enough for the plants’ healthy growth. Calcium and magnesium are the most common supplementation in an aquaponics system that uses pH-raising supplements to moderate the pH level.
Micronutrients in Aquaponics
- Copper: usually included at high levels is the fish food.
- Zinc: Common in fish foods and as the galvanized steel components that make their way into aquaponics systems.
- Boron: mostly in most aquaponics systems. Boron is required at low levels in aquaponics.
- Molybdenum: Required at low levels in aquaponics.
- Chloride: usually enters the systems through the fish food in the form of salts.
Non Mineral Nutrients in Aquaponics
Non-mineral nutrients are essential for the growth and development of aquaponics plants. The oxygen is delivered through water, but for it to be sufficiently available in the system, aeration must be added.
The Most Common Deficiencies in Aquaponics Systems
1. Iron Deficiency
Plants need iron for the formation of chlorophyll. Iron is one nutrient deficiency that needs to be managed regularly, especially if the pH is high. Plants will have difficulty absorbing iron if the pH is 8.0 or higher.
Signs of Iron Deficiency:
- Yellow color on plant leaves
- Spots on immature leaves
How to supplement iron:
To increase iron in your aquaponics system, you need to add iron that can be absorbed by the plants. This means using “chelated iron.” Adding chelated iron to your system will only be effective if your pH is 7.5 or lower. Your aim is 2 mg/liter, so you need to calculate your water tank’s size and add the required amount of iron every 3 – 4 weeks.
Potassium is important for photosynthesis, gas exchange on the leaves, and synthesizing proteins. Potassium deficiency affects the flowering and fruiting of plants.
Sign of Potassium Deficiency:
- Older leaves of the plants show interveinal chlorosis and spots or scorching, which progresses to the younger leaves when the deficiency becomes more severe.
How to supplement potassium:
- By Spraying – You can use potassium chloride and spray it into the plant leaves. This process must be repeated at least once a week to avoid potassium deficiency in your aquaponics plants.
- By adding a potassium supplement to your fish food through kelp meal, concentrate. Other options are adding potassium sulfate or potassium hydroxide to your fish food.
Calcium is important for regulating the osmotic pressure and for the cell wall structure of the plants. Calcium deficiency can sometimes be attributed to plants not losing water.
Sign of calcium deficiency:
- Black, dead areas of the young plant tissue, known as necrosis.
- Slight chlorosis to brown or black scorching on new leaf tips.
- Fresh leaves are distorted with hooked tips and irregular shapes.
How to supplement calcium:
- One way to supplement calcium deficiency in aquaponics is to use hydrated (or agricultural) lime, which will also supplement calcium and magnesium besides raising the pH levels.
- Another way is by spraying calcium chloride mixed with some water to your plants. The ratio should be four teaspoons of calcium chloride per gallon of water. You can increase the dose if needed and spray once a week to your plants.
Phosphorus is important for the distribution of energy, protein cellular, and metabolism of the plants.
Signs of phosphorus deficiency:
- Stunted plant growth.
- Darkening of the leaves near the plants’ base.
- Purple or reddish color of the leaves.
- Spare leaf growth.
How to supplement phosphorus:
The most common method to add phosphorus to aquaponics is to use rock phosphate. The supplement can be added directly to your grow beds. Avoid adding it directly to the water, and your grow bed should be shaded from the direct sunlight to ensure that it doesn’t dissolve before the plant can absorb it.
The best way to ensure that plants will not suffer nutrient deficiencies in aquaponics is to maintain the 6-7 pH water level and feed the fish with a balanced and complete diet. Another good way is to provide all the nutrients that plants require to grow by using growing media beds. Grow media beds offer an excellent environment for nutrients to develop into your system, and you can also add worms in your grow media bed to help break the solids and provide more nutrients for your plants.
Management of nutrient deficiencies in aquaponics is not challenging to do if you know the basics. However, to ensure that your aquaponics system runs smoothly, it is essential to use a balanced fish food for the fish. Regular monitoring can also help avoid nutrient deficiency in aquaponics. Thank you for reading our blog. Join our Facebook group for more information and discussions from our international community.