8.5 Tiny Bytes Soil Electrical Conductivity Made Simple

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And now it's time for a tiny bite of knowledge.
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Sarah, do you want to hear a shocking fact?
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Only if there's not a lot of resistance involved.
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Did you know that soils conduct electricity?
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That's shocking and very electric.
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That's good timing.
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That's great timing.
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Today we are going to talk about electrical conductivity.
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And long story short, yes, soils can actually conduct electricity.
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Specifically, soil electrical conductivity measures the ability of soil water to carry electrical current.
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There are a number of parameters that influence the amount of electrical conductivity in the soil.
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These things include and are largely related to the amount of soluble salts that are in the soil solution or the soil water.
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So, like how salty the field is.
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Exactly.
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Exactly.
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So a lot of times when you see your soil sample results coming back from the lab, you'll see like soluble salts and it's measured in Moes per centimeter sometimes on the bottom of a soil test.
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Mo is literally the opposite of ohm.
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If you remember back to basic electric class, ohms are a measurement of the resistance of electrical conductivity, whereas MOS are actually the conductance, how well electric electricity conducts.
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So things that influence electrical conductivity include soluble salts in this in the soil water, uh porosity, soil texture, especially your clay content and mineralogy, soil moisture and soil temperature.
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So remember, we had an episode a while back on tiny bites talking about cation exchange capacity or the fact that the negative or the fact that soils with clays in them conduct electricity.
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And that can exchange capacity doesn't include just clays, it also includes organic matter as well.
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And so that is a factor, a factor of um what can also increase or affect EC or electrical conductivity values in the field.
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And so when we think about all these things, if we can measure what EC is at a point in the field, there's an ability to look at it across the field and see where differences are in the field based on these factors.
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Absolutely.
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So there's many different ways that we can measure uh soil electrical conductivity.
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We can take bulk soil samples and send them into the lab and get them analyzed.
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We can do on-the-go measurements, such as using a Varus tool or an EM38.
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Some places call that a swap box.
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So there's many different ways that we can measure um soil salinity.
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So one thing that's really important, and I'll just talk briefly about like, okay, what does it mean to um measure EC from a lab result, and like how does that relate to the on-the-go measurements?
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I'll just cover that briefly.
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Um, but basically, right, so instead of getting a whole field mapped, you might have a zone sample map where you're sampling different zones and then sending that sample off to get the EC value for that place in the field.
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And what I really want to drive home in this point is that these EC values that you're gonna get back from the laboratory, those are gonna be standardized values.
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So you can compare those EC values from one field to the next.
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You can compare them from one field to the next, you can kind of compare them from one year to year.
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They're standardized.
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So, like when you send that soil in, they're going to dry that soil sample and then they're gonna add a known amount of water to it, and they're gonna put that electrode to measure the electrical connectivity of that soil sample in for a standardized amount of time.
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Therefore, factors such as different moisture levels or um like porosity, those won't be as much factors as say if they are in the field, meaning that when you get that EC result on the soil test report, you're gonna get a standardized value that you can then compare to like um guidelines of like, okay, what is considered saline uh based off of an EC of X or what is not saline fairly standard values.
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But the drawback is that again, we don't have the ability to poke holes on every single part of our fields, that's not practical, and send a test on it.
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We can't really do a big picture of the whole field.
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We can zone sample and we can guess what those values might be in between, but we don't get the whole picture of the field.
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Right.
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And so the reason that that becomes a standardized test is because there is a that you and you said this when you're explaining it, there's a finite amount of water that is going into that sample.
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So it doesn't matter what field that soil comes from, it's going to have a known amount of water to mix with that soil solution to dissolve the salts.
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So when you mix that electrode in there, literally what you're gonna be measuring are the components of that soil that conduct electricity.
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Remember, salts dissolved in water, the more salts there are in that solution, in that water, the better it's gonna conduct electricity.
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So if you are standardizing the amount of water that's going into that solution, it's going to be able to be comparable across all those different soils.
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Now, when you get a map coming from some of those on-the-go um monitors like uh Varus or EM38, that's very useful data because, like you said, you're getting values all across the field.
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You're driving so far, and as you're going, there's electricity current that's basically being emitted from each one of those devices, and the amount of current that gets returned back to those devices is logged.
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It is literally the electrical conductivity.
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But in that scenario, you don't have that standard amount of moisture within this the field or the grinding that's happened to change the porosity out there, like what you get with that lab result.
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And therefore, that is not gonna necessarily be a standardized result, but you can see the variability within that given data set.
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Oftentimes, for example, when you are using um uh varus, for example, you're gonna take some soil samples with that that you're gonna send to the lab so you can kind of calibrate that data and get a better idea of what it exactly means.
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Um, but yeah, so there's some differences there.
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So you can send in soil samples to the lab and get an indication of standardized soils.
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You can do on-the-go monitoring so you can map out the entire field and see the differences.
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But I also think it's important to talk about like what are the values that we're getting back?
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Like, what exactly is a salty field?
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Can we back up for a second though?
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So you mentioned on-the-go measuring devices, and can you talk a little bit more about what the difference between like a Varus and EM38?
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So, Varus actually has discs, and you pull it across the field, and those discs actually send soil current into the ground zero to 12 inches down or down to like and then zero to three feet.
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So you can actually see shallower soil salinity and deeper soil salinity.
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Um, and it's gonna show you the amount of conductance um from that current current, and then again, you actually have to calibrate it back to soil core.
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Now, Varus is a great tool.
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I have seen some people do some amazing mapping off of that, but again, if the soil moisture is too dry in that field, then there's not gonna be enough water, soil water there to conduct electricity, and you're not gonna get good readings.
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I have also seen some not good maps and some extremely dry conditions.
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So that's just one thing to know.
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Um, if it if it is a very dry fall, it might not be a good year to be bogging that.
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Um, an EM38, or some people talk about a SWAT box out there, uses both conductivity and magnetic susceptibility.
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Um, instead of having discs on the ground, you actually drag it, almost looks like a little bar, and then sometimes people put it in like a plastic sled and they drag it across the ground, and that is actually um pushing electrical um signals, electricity in the ground, and it's also um determining on the amount of conductivity as well because the varus actually has disks disks in the ground, and because the EM38 does not, sometimes we see a little bit better uh data coming off of the EM38 as far as overcoming dry soils.
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But again, it's still really important to know that even the EM38 is is susceptible to dry soils.
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You still have to be careful with it.
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And for both of these items, if you really want to understand what that variability means to the field, you should really pull some soil samples in some very different areas across the field so you can actually calibrate that that data back to real lab analyzed results.
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Yep.
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I think that's a really important thing to mention.
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And just like we talked about at the beginning, in terms of like the factors that affect um EC value measurement, there's a lot of things that kind of overlap, right?
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And so in North Dakota, you've got, yeah, you're probably gonna see like what your really high EC values are.
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You're gonna see what your salty, really, really salty spots are, but you get a little bit lower for conductive conductivity and like the mid-range.
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Is that due to a difference in soil texture because you're got really high clays, or you've got two different types of clays that are there?
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Is that what's causing the EC difference?
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Is it because of higher moisture content?
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Is it because of compaction?
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There's a lot of factors that um go into what actually affects that final EC value.
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And so thinking about this is I think really these EC maps are great at figuring out where differences exist in the field.
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And yeah, probably pointing out where your really salty areas are too.
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Um, but just know that sometimes it can be really hard to just comb out a single factor or sing or or do something like, and here in North Dakota where we have a lot of salts, I wouldn't ever, you know, use the map to say exactly where my um where my clay content, my high clay content areas are.
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Um, it's just a little bit harder to to pull those out when there's so many factors that influence the measurement.
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So let's talk about what does it, what are some of these values coming back from the lab look like if you have a salty soil or non-salty soil.
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Um and um the measurement for electrical conductivity that we use for soils is often desiemens per meter or moes per centimeter.
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Fun fact a mo is a measure of, and that's spelled mm-h.
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It is a measurement of conductance.
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If you remember back to physics class back in the day, there's also a thing called an ohm.
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That is a measurement of resistance.
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So literally, an ohm is resistance and a MO is conductance.
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They're inverse, isn't that fun?
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I love how the camera zoomed up at the end.
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That was dramatic effect to the max.
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I know it was terrible.
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And and all I was gonna say is like the routine soil test result that you get is gonna be, you know, your EC and decisiemens per meter.
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Um, and NDSU, anything over an EC of four is considered saline.
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Uh, just know that, you know, if you're looking at your various or EM38 data, again, since it's relative and not, you know, a standardized test, you're likely gonna see numbers that are much higher than four.
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Um, and that doesn't necessarily mean or does not mean that you've got a saline soil that you're working with.
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But I just one thing quick.
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Sarah and I do have previous tiny bite episodes that do talk about some of these differences in saline and sodic soils, um, and also um things like soil charge and cation exchange capacity, which I will make sure to include in the show notes for this episode.
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That would be shocking.
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Did you want to talk about more measurement values?
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So I'm feeling insulated from this conversation.
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I just have the song It's electric stuck in my head.
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We're gonna be doing the electric slide for the rest of the day.
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That is so dramatic.
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It was dramatic and electric.
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Tune in next time for a tiny bite of knowledge from GK Technology, where we have a map and an app for that.