Sulfur is one of the secondary macronutrients and is very important to plant production.
In aquaponic systems sulfur is rarely deficient.
Its one of the reasons you hear about it so often.
In fact, sulfur is more often present in larger-than-necessary quantities, primarily because we love to use supplements that are sulfate based.
Sulfur occurs in solution as sulfate, SO42-, a soluble anion. Sulfate is taken up directly by the plant and is very important in the production of many amino acids, proteins and oil production.
In many crops, sulfur is as important as phosphorus to plant growth and development! Without enough sulfate, plants will be spindly, with yellowed new growth.
Sulfur deficiencies and toxicities are rare
In many crops, sulfate deficiency is often confused with other deficiencies. However, in aquaponics systems, sulfate deficiencies are rare.
Sulfur toxicities are also rare. Many aquaponic enthusiasts are very concerned about excessive sulfates impacting their plant production. The truth is that in aquaponic systems sulfates will almost never be excessive to the point of impacting plant production, and even when they are, plants are great at both taking up excess sulfate and storing it as well as regulating the intake of sulfate.
This means that even if your sulfates run high, you neednt worry too much about toxicity. You can worry about your cabbage being smellier than usual, but thats about the extent of the damage that high sulfates can do in most aquaponic systems.
Sulfur can be supplemented with other nutrients
Does this mean that more growers should lean on sulfate based supplements? The answer to this question is only when appropriate. Because sulfate is seldom deficient, you shouldnt be concerned about supplementing it as a grower.
However, in systems where the pH runs high and causes the availability of other nutrients to suffer, sulfate based supplements can be a great way to get system nutrition back on track. Potassium sulfate and magnesium sulfates are great examples of this. Ideally, these two plant nutrients would be being supplied as hydroxides, or in systems with very low pH values as carbonates. In high pH systems this isnt possible, so in these instances the use of either potassium sulfate (0-0-50!) or magnesium sulfate (Epsom salt) can be a very fast and effective way to supplement these nutrients in solution.
At Bright, weve pioneered the use of sulfates as system supplements, and slowly folks are catching on to the benefits they can offer. Because theyre a new concept to many growers, theres a great deal of hesitancy about starting to use them. I hope that this post helps illustrate that while they shouldnt be used willy-nilly, sulfate based supplements can be a powerful tool in the hands of an aquaponic grower.