Surprising spikes in root zone EC

“EC” (or “electroconductivity”) is short-hand for nutrient concentration in a water solution.

The measure is based on the principle that it’s easier to pass an electrical current through salty water than pure water, because the salt ions conduct electricity better than pure water molecules.  EC measurements can be used to measure soluble nutrient concentrations in both field soil and media, but is a measure more commonly used in media.

Handily, the EC measurement is directly proportional to the ion concentration of the liquid feed, making it a pretty good proxy for nutrient concentration.  EC doesn’t tell us which specific ions are making up that concentration, whether they be NO3- or K+ or something the plant doesn’t need like sodium.  However, with a known nutrient recipe input, it’s a quick, useful measure of liquid feed strength and drain nutrient concentration.

In practice, tabletop strawberry growers often use drain water nutrient testing to extrapolate what is present in the strawberry root zone.  Drain water measurements are similar to the “pour through” EC test, a method used in potted crops that catches the first few millilitres of drain from the bottom of a container after the plant has been watered.  Tabletop growers can compare the EC in the feed to the EC in the drain to know whether plants are taking up more or less nutrient than they are being given.

This season we’ve been using soil moisture and EC sensors from Tau Research, in a project supported by the Horticentre Charitable Trust, to track both moisture and nutrient concentration (EC) in the root zone of our variety trials.

One thing we’ve noticed with the meters is that when we let the soil dry down, the EC spikes.

Below are the graphs showing what’s happening to the EC in the root zone as the media dries down.  We’d been tracking along in the normal range of EC 1-2, but as we got dry one afternoon the root zone EC got higher, spiked a couple times, and dropped back down after we watered.

‍

The example above shows a relatively mild dry down, but it’s interesting because soil EC is roughly inverse to soil moisture.  We don’t normally see what’s happening in the root zone without adding water to flush out a liquid sample to measure, but what happens in a dry soil is that the nutrients (ion salts) concentrate.

One of the reasons why strawberries suffer when they dry out can be because of high salts injury to the roots.

‍