Calcium in aquaponic systems
A common nutrient in aquaponics
The fact that this is debated speaks to its importance in the plant growth cycle. Calcium is a common nutrient in aquaponic systems and is not usually deficient due to pH (although if you run very low pH, it can impact availability!).
Most water is fairly hard, so calcium enters the system every time the grower tops his system off in the form of calcium carbonates. In healthy systems, these carbonates are quickly consumed, leaving the calcium for plant uptake.
Calcium uptake is passive
Calcium is an interesting nutrient because while its very important, plant uptake is very passive. Basically, plants take up calcium as they take up water. While plants actively take up other nutrients, calcium uptake is limited by the concentration of calcium in the solution and by how much water the plant takes up.
This is important to understand, because with some crops calcium deficiencies have nothing to do with concentrations, pH or any of the common deficiency culprits.
Sometimes calcium deficiencies occur simply because your crops are not well ventilated, and humidity is too high. This means that the plants are not transpiring (losing water through their leaves) very much, which means that they arent taking up much water, which means that they arent taking up enough calcium.
Signs of calcium deficiency
Its important to know what youre looking for when it comes to calcium deficiencies. Calcium deficiencies in some instances can imitate Potassium and Magnesium deficiencies, with the chief difference being black, dead areas of young and growing plant tissue. (Because Calcium can imitate other deficiencies, use a key to diagnose!)
Usually, this is apparent at the growing areas at the top of the plant. The young tissues die first because plants arent very good at transporting calcium within the plant. It is one of the elements that are immobile in the plant. This is because calcium is often used as a kind of structural material, helping to hold together cell walls. For this reason, calcium is a lot like cement. Once its been used, you cant really move it and reuse it.
Treating calcium deficiencies
If youre certain that youre seeing a calcium deficiency, you have a few treatment options.
If you want to balance your system Calcium in solution, you should look into hydrated lime additions (low pH systems), calcium carbonate (very low pH systems), chelated calcium additions, or foliar applications of calcium chloride.
The best treatment option (in our opinion)
Calcium chloride foliar applications are the best way to supplement calcium and see results quickly. I typically recommend around 1 tsp/gallon of water to start.
Caution: salt alert
The same caution applies to calcium chloride as it does to potassium chloride- you are applying a salt, so apply carefully in very low volumes early in the morning or preferably, at dusk. Remember, when doing foliar applications, it is always better to apply low concentrations more frequently than to apply higher concentrations with less frequency. Caution is always recommended!
Other treatment options
For these other supplements, dose based on your system pH. Here at Bright Agrotech, we use a lot of hydrated (or agricultural) lime as well as potassium hydroxide to raise pH. This naturally supplements calcium as the pH is moderated.
If your system has a neutral to high pH, then chelated calcium can be a great way to get calcium to your plant roots. The amount you add will really depend on your particular system.
If you have the means to test calcium in your aquaponic systems, you should be shooting for at least 40-70 ppm calcium (with other nutrient levels at recommended levels! See other blog posts.).
If dont have the means to test calcium, then regular calcium dosing at low levels (i.e. to control pH within a certain range) is unlikely to hurt your system. Your system will tolerate relatively high levels of calcium, but high levels (in aquaponic systems 120-150 ppm +) can begin to interfere with uptake of other nutrients.
Note: This is only for aquaponic systems. Hydroponic systems can tolerate higher concentrations of calcium in solution since the solutions are typically better balanced in regards to other plant nutrients.
Nutrient Deficiency Key