In order for your plants to flourish they will need a balanced supply of mineral nutrients. The majority of plant nutrients will be contained in your fish feed but some will still need to be supplemented. Understanding nutrient flows in your system and knowing how to detect certain deficiencies is an important part of maintaining a healthy and productive system.
Plant nutrients can be split into two main categories, ‘macro’ and ‘micro’ nutrients. Macro nutrients are required in greater abundance and micro nutrients or trace elements, as they are sometimes referred to, are only required in minute amounts. For classification purposes macro nutrients can also be further broken down into primary and secondary nutrients as is detailed below:
- Primary: Nitrogen, N; Phosphorus, P; & Potassium, K.
- Secondary: Calcium, Ca; Magnesium, Mg; and Sulfur, S.
- Copper, Cu; Zinc, Zn; Boron, B; Molybdenum, Mo; Iron, Fe; Manganese, Mn; Chloride, Cl.
The most common nutrients found to be lacking in an aquaponics system are iron, potassium and calcium. For more information on correcting these deficiencies please see the aquaponics additives blog post.
Testing for individual nutrients in a backyard system can be expensive. It is therefore advantageous to be able to identify deficiencies if and when they do arise. The table below identifies a range of nutrients and their associated signs of deficiency. N.B. Only the important micronutrients for aquaponics have been included in this table.
|Primary||Signs of deficiency||Comments|
|Nitrogen||– yellowing of older leaves
– rest of the plant is often a light green
|– required in abundance by green leafy plants
– essential part of all protein, enzyme and metabolic processes
– essential for photosynthesis
|Phosphorus||– stunted growth
– leaf tips look burnt
– red and or purple leaves and stems
|– encourages blooming and root growth
– essential for photosynthesis aids in the formation of oils, sugars and starches
|Potassium||– brown scorching and curling of leaf
– yellowing of leaves starting from the outer edge
|– required in abundance by fruiting plants|
|Secondary||Signs of deficiency||Comments|
|Calcium||– new leaves grow irregularly
– can lead to blossom end rot (discoloured, sunken spot presenting at the blossom end of fruit)
|– essential part of cell wall structure|
|Magnesium||– leaves turn yellow at edge however area between veins remains green||– essential for photosynthesis|
|Sulphur||– younger leaves yellow first||– serves various roles in the plant|
|Micro||Signs of deficiency||Comments|
|Iron||– yellowing of entire leaf||– easily affected by pH (iron lockout at high pH)
– common deficiency in aquaponics
It is also important to be aware that the pH of your system can further determine the availability of certain nutrients in your system. Nutrients like Iron and Manganese are only available to the plant at lower pH’s. It is advisable therefore to try and keep your pH somewhere between 6 and 6.5 for maximum nutrient uptake.