This roundtable was originally published August 21, 2015.
About the Upstart Farmers Roundtables
Upstart Farmers Roundtables are an informal, biweekly event. Using Google Hangouts video calling, a small group of Upstart Farmers comes together to share their experiences and learn from each other. Each week is guided by a discussion topic, with growers welcome to ask their own questions.
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Roundtable: EC: Electrical Conductivity
What is EC?
EC is a measurement of the electrical conductivity of a solution. In other words, you are measuring the salts in the solution, and therefore the nutrient content in the solution (in hydroponics).
What does EC not tell us?
It does not tell us the concentration of individual nutrients. We’re relying on a nutrient solution to make sure that plants are consuming certain nutrients at certain rates. We just assume everything is being consumed at a rate in the formulated solution. It does tell us what the general concentration looks like.
What can we manage with EC?
In hydroponic solutions, EC and pH are two main measurements we take. EC tells us the amount of nutrition in the solution and pH tells us how available it is.
We’re just measuring the soluble salts in the solution. Therefore, we can manage the salt levels, i.e. fertilizer in the solution.
How is it measured?
We pass a current across electrodes and the strength of that current tells us the salt concentration of the water. The more salt in the water, the more conductive it is.
Why is it important?
This is important in hydroponic systems because we’re putting inorganic salts into the system which are the primary source of our fertilizer. We add the formulated solution until we hit a certain EC value, then it will drop as the plants consume those nutrients, and then we add it again until we hit that level we desire.
If everything is being consumed at the right ratio, then we can fine tune and manage our nutrition quite well just with that single measurement.
How is this different in aquaponics?
While EC is a semi-useful measurement in aquaponics, it really does not hold the same value as it does in hydroponics.
In systems that are cycling well and really stable, EC can be used for some information but it is still not particularly useful. It can be useful if people are salting their system with something Epsom salt.
Reason being, in aquaponic systems, we’re seeing organic solids breaking down into inorganic solids. They still become the exact same nutrients, but as soon as those nutrients are created or freed from the organic compounds that were holding them, they are immediately absorbed by the plants and microbes. Aquaponic systems are so biologically active that the life of the say, phosphate molecule, is very short. Whereas in hydroponic systems, there is not much biology to interfere and the nutrients just sit in the solution until they are gradually absorbed.
Can you use EC to manipulate plant growth and flavor?
Yes. Many people still mix by hand, but dosing equipment really opens up a whole new realm of management practices for growth and flavor.
Osmotic potential in semipermeable materials like plants, causes water to flow to areas of low solute concentration to areas of high concentration. So, when EC is in a solution is really high, the plants have to work hard to absorb water. If the solution is saltier than the water in the plant cells, then the solution will actually pull water out of the plant. In order to balance this out, the plants have to create a higher level of solutes in their cells which generally means they produce more sugars.
For example, tomato growers now days have figured out that setting different EC values at day and night allows them to make the tomatoes sweeter. They challenge the plants with more salts at night. This throws off the osmotic balance and forces plants to produce more sugars to uptake water, therefore making the tomatoes sweeter.
EC can also be used to create field-like stress factors like simulated drought to create a more natural, field-crop flavor in the plants.
For example, if you drought-stress basil, you can create a more bitter flavor and make it more aromatic. You can do the same thing by hitting it with excess light and not enough water. If we manage the EC in the right way, it that allows us to make “designer flavors” for our plants. Pretty cool!
What are the most effective way to change EC levels? Is there a difference in managing it in hydroponics vs. aquaponics?
In hydroponics, it’s simple, you either add fertilizer or salt, or dilute the solution with water.
In aquaponic systems, we don’t have that level of control because we’re trying to find system stability by keeping our plants, microbes, and fish happy. While plants are pretty tolerant to swings, microbes and fish are not. You have to be more careful about adjusting your EC because it can cause some aspect of the system to go off balance and die.
Most of our ability to control EC happens in hydroponic systems. The good news is, dosing systems give us much more control. And, in the near future, there will be hand-held spectrometers that allow us to identify the exact levels of specific nutrients in the solution.
What does EC mean in organic systems?
EC is not a totally useless measurement in organic systems; it’s just not as powerful as it is in hydroponics.
If we’re able to measure nutrients in a somewhat automated way, we can use EC to index where we’re at, assuming we’re keeping all other levels the same. If we’re feeding the same rate and our biomass is very stable and predictable, then it can be one of a few variables that are easier to measure and give us a good idea of the nutrients in our system.
Is EC a good measurement for when you’re using compost teas?
Yes, EC can be a useful measurement for judging the quality of your compost tea. If you test for the EC of your compost tea before you add it to the solution, it will tell you whether or not this is a good “batch.” If you reading comes back showing that your compost tea is really salty, or not salty at all, then you know you have a problem and probably don’t want to add that batch to the system.
It’s important to note that Dr. Nate generally does not recommend the use of compost teas. He tried used them for many years and realized that ultimately they cause more problems than it is worth. Unless you have a very consistent and unchanging set of materials going into the compost each batch, the nutrient quality will vary with each batch. This removes your ability to properly manage for individual nutrients and can gum up your system. It’s always better just to use a formulated solution in your system.
If you are going to use compost teas, keep in mind that vermicompost teas tend to have higher EC values than standard compost teas.