Part 1: Irrigation of Controlled Environment Crops for Increased Quality and Yield

What you need to know to get the most out of your substrate, so you can maximize the yield and quality of your product.

Part 1: Substrates and Water

Stop guessing. Start measuring.

When you irrigate in a greenhouse or growth chamber, you need to get the most out of your substrate so you can maximize the yield and quality of your product. But if you’re lifting a pot to gauge how much water is in the substrate, it’s going to be difficult—if not impossible—to achieve your goals. To complicate matters, soil substrates and potting mixes are some of the most challenging media in which to get the water exactly right.

Without accurate measurements or the right measurements, you’ll be blind to what your plants are really experiencing. And that’s a problem, because irrigating incorrectly will reduce yield, derail the quality of your product, deprive the roots of oxygen, and increase risk of disease.

Supercharge yield, quality—and profit

At METER, we know how to irrigate substrates. We’ve been measuring soil moisture for over 40 years. Join Dr. Gaylon Campbell, founder, soil physicist, and one of the world’s foremost authorities on soil, plant, and atmospheric measurements, for a series of irrigation webinars designed to help you correctly control your crop environment to achieve maximum results. In this 30-minute webinar, learn:

  • Why substrates hold water differently than normal soil
  • How the properties of different substrates and potting mixes compare
  • Why it’s difficult if not impossible to irrigate correctly without accurately measuring the amount of water in the substrate
  • The fundamentals of measuring soil moisture: specifically water content and electrical conductivity
  • How measuring soil moisture helps you get the most out of the substrate you choose, so you can improve your product
  • Easy tools you can use to measure soil water in a greenhouse or growth chamber to maximize yields and minimize inputs

Next steps


Our scientists have decades of experience helping researchers and growers measure the soil-plant-atmosphere continuum.


Dr. Gaylon S. Campbell has been a research scientist and engineer at METER for over 20 years, following nearly 30 years on faculty at Washington State University. Dr. Campbell’s first experience with environmental measurement came in the lab of Sterling Taylor at Utah State University making water potential measurements to understand plant water status.

Dr. Campbell is one of the world’s foremost authorities on physical measurements in the soil-plant-atmosphere continuum. His book written with Dr. John Norman on Environmental Biophysics provides a critical foundation for anyone interested in understanding the physics of the natural world. Dr. Campbell has written three books, over 100 refereed journal articles and book chapters, and has several patents.


See all webinars

Part 2: Irrigation of Controlled Environment Crops for Increased Quality and Yield–Nutrients and Osmotic Stress

In this 30-minute webinar, world-renowned soil physics expert, Dr. Gaylon Campbell discusses how to measure EC and osmotic stress to optimize crop steering for maximum yield.


Part 3: Irrigation of Controlled Environment Crops for Increased Quality and Yield

Get the information you need to stress or de-stress your crop at the right time and in the right way to achieve your goals.


Part 4: Irrigation of Controlled Environment Crops for Increased Quality and Yield

Dr. Gaylon Campbell teaches what is required in controlled environments to ensure all environmental variables remain balanced for the highest possible efficiency and production.


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Hello, everyone, and welcome to part one of our webinar series, Irrigation of Controlled Environment Crops for Increased Quality and Yield. Today’s presentation will be about 30 minutes, followed by about 10 minutes of Q&A with our presenter, Dr. Gaylon Campbell, whom I will introduce in just a moment. But before we start, we’ve got a couple of housekeeping items. First, we want this webinar to be interactive, so we encourage you to submit any and all questions in the Questions pane. And we’ll be keeping track of these for the Q&A session toward the end. Second, if you want us to go back or repeat something you missed, don’t worry. We’ll be sending around a recording of the webinar via email within the next three to five business days. All right, with all of that out of the way, let’s get started. Today we’ll hear from Dr. Gaylon Campbell, who will discuss how to get the most out of your substrate and correctly control your crop environment to achieve maximum results. Dr. Campbell has been a research scientist and engineer at METER for over 20 years, following nearly 30 years on faculty at Washington State University. His first experience with environmental measurement came in the lab of Sterling Taylor at Utah State University, making water potential measurements to understand plant water status. Dr. Campbell is one of the world’s foremost authorities on physical measurements in the soil plant atmosphere continuum. His book written with Dr. John Norman on environmental biophysics provides a critical foundation for anyone interested in understanding the physics of the natural world. He has written three books, over 100 refereed journal articles and book chapters and has several patents. So without further ado, I’ll hand it over to Gaylon to get us started.

Okay, thank you. METER builds sensors for monitoring both the above and below ground environment of plants. Our past seminars tended to focus on the outdoor environment, but the sensors are just as applicable to indoor controlled environment crops. We intend this to be a series of seminars on applications in controlled environment crops. Today we’ll talk about managing water in some of the substrates that are typically used for controlled environment crops. In later seminars will talk about measuring and controlling nutrients, uptake and water loss, and salt balance. Best selling author Clayton Christensen wrote a book a while ago, where he analyzed the suitability of certain products for certain markets in terms of jobs to be done. And we can use that approach in analyzing the suitability of substrates in a controlled environment crop production. When we select and purchase a substrate for a crop, we are in effect hiring the substrate to do jobs for us. And what are those jobs? Well, it’s perhaps obvious but the substrate needs to hold up the plant. It also needs to supply water and nutrients to the roots of the plant. Substrates that are used in controlled environments typically contain few, if any, nutrients and have very little, if any, exchange capacity for the nutrients. The nutrients therefore, typically are supplied in the water. Another important job to be done by the substrate, and one that is sometimes overlooked is the supply of oxygen to the roots. The ability of the substrate to do these jobs is strongly dependent on the knowledge and skill of the person or the system doing the managing. And many of you who are watching this seminar, have that responsibility, and I intend to share some principles and information with you that’ll make you more skillful and able to manage the water and nutrients in controlled environments better. Before we talk about water in substrates, we need to provide a little bit of background. We’ll do that with some questions and answers.

The first question we might ask is why we need to irrigate in the first place. We know that plants, like us, need water. Life processes are sustained by a series of biochemical reactions that can only occur in a highly hydrated environment. We, like plants, live in a pretty dry environment. Our problem is to get oxygen from that environment. And we lose water in the process with every breath we take. The plant needs carbon dioxide from its environment, and that’s a lot less plentiful in the atmosphere, than the oxygen is. The plant therefore loses a lot of water, in the process of taking up the carbon dioxide that it needs for photosynthesis. That water is replenished by the roots, the soil substrate, and so we irrigate to replace the water in the substrate.

The next question we could ask is, What are the forces that cause water to move? We all know that water runs downhill, but in plants, it moves up. Some force greater than gravity must be pulling the water up. Water moves from regions of high energy in the substrate to lower energy in the leaves, and eventually, to the atmosphere where the energy state is the lowest of all. The path the water follows from the soil through the plant to the atmosphere, we call the soil plant atmosphere continuum, or SPAC. Now here I’ve tried to quantify the energy state of the water in the SPAC. We call a measure of that energy, the water potential. And here I show it in two different forms, we can measure it as a pressure, that’s the column labeled kilopascals on the left, or as a relative humidity here, more appropriately water activity, and that’s the column on the right. That thinking in terms of relative humidity might be more familiar to you. Let’s look at that column, the relative humidity column. In the soil, the humidity might be something like 99.998%. Pure water, of course is at 100%. So you can see that the soil water has an energy state very close to pure water. The humidity at the root surface is a little lower, so the water can flow, but that difference is pretty small, too small to show the numbers we have here. Significant drop though occurs as the water moves across the route into dermis. So the humidity there, we show, is 99.49%. Xylem to leaf, it’s a little lower at 99.28%. But the big drop off is going from the leaf to the atmosphere where we show it at 48%. Now this is just a hypothetical example. But the values that we have here are typical of what we might find in a well watered plant. And I think it makes some important points. One is that the inside of the plant is indeed highly hydrated, very close to 100% humidity. The main resistance to water loss is not within the plant itself, but as the water evaporates, and diffuses through stomates and into the atmosphere. A relative humidities give us some good insights, but they’re not very convenient to use as measures of water potential. Pressures are a lot more useful and convenient. And I want you to note that the pressures here are all negative. Pure water has a water potential of zero. Since the water in the SPAC has less energy than pure water, we show those values as negative values. So what determines the water potential in the plant or in the growth medium? A number of factors could influence the water potential, but the three most important are the ones that I show here. The matric potential of a substrate or soil is a measure of how tightly water is absorbed on particle surfaces or held in capillaries or interstices. If we put the end of a dry sponge in a shallow dish of water, the water will move up the sponge. Matric forces in the sponge are pulling the water up against the force of gravity. The second kind of forces are osmotic. When a semipermeable membrane exists, which allows water to pass but prevents the movement of solutes that are dissolved in the water, a difference in concentration of solutes across the membrane will result in an osmotic potential difference that can cause water to move. The important membrane in the SPAC is at the root endodermis, where the water is taken up, but solutes that are in the water are preferentially either taken out or rejected according to the plant’s needs. A second important membrane is an interface with air. Water can evaporate and cross the membrane; solute can’t evaporate so they’re left behind. Gravity always needs to be taken into account in determining the water potential, especially in the kind of substrates we’ll talk about today that have large pores and gravity plays an important role in determining the distribution of water and substrates like these. Finally, I’d make a point that the total water potential is the sum of the components and so both the matric and osmotic forces are important to the plant as it takes up water.

Now a more familiar measure of moisture in a soil or rooting medium is its water content. We’ll talk about volumetric water content here, that’s the volume of water per unit volume of soil. We multiply that by 100. We get a moisture percentage. And that’s the most common way that people express that. In this graph we show the percent water for a typical silt loam soil for a range of matric potentials. And each point represents an actual measurement that we’ve made. METER design,s builds, and sells equipment for characterizing porous media in this way, and that way of being able to do it gives insights that are otherwise unavailable. Let’s note a couple of things. The matric potential is in centimeters of water rather than kilopascals. A kilopascal is approximately equal to 10 centimeters of water. Water potential in centimeters will be easier for us to visualize as we discuss the water in soil of substrates like the ones we’ll be talking about today. The matric potential scale is logarithmic in this graph so that we can see the detail at the wet end and still see what happens at the dry end. Matric potential is a negative number, but, of course, logarithms of negative numbers aren’t defined. So we show them as positive numbers on this axis, but we’ll speak of them as negative numbers. Now notice that between minus one and minus 10 centimeters of water, water content is almost constant around 52%. That’s the saturation water content of the soil. All of the pore spaces filled with water, so there’s 52% water and 48% soil minerals, making up the total volume. Lowering the potential beyond minus 10 centimeters starts to desaturate the soil so air starts to go into the pores. And by the time we get to minus 1000 centimeters, the water content has decreased to around 25%. Now we call these curves moisture retention curves because they show us the amount of moisture retained at each energy level. Here we contrast the retention curve of a common controlled environment substrate rock wool with that silt loam soil that we had in the last slide. And the two things should be obvious. One is the saturation water content of the rock wool is much higher, around 95%. So the solids in the rock wool take up only about 5% of the total volume compared to 48% for the silt loam. The other thing to notice is that the rock wool releases its moisture much more easily than the soil does.

Now, here are some moisture retention curves for several substrates that are used in controlled environments, compared to that silt loam soil. You can see that the rock wool and silt loam represent, sort of, end members in a continuim. Rock wool has many large pores and few small ones, so it holds water loosely. The silt loam has many fine pores and few large ones, so it holds the water much more tightly. Now to make sure that you fully understand these ideas, let’s look again at the rock wool in the coco coir. Let’s say the range of water contents over which we might expect to operate is 30 to 70%. These are shown as circles on the graph. Is the added water content to 70%, both have a water potential of minus 10 centimeters water. The plant would have to apply a suction of 10 centimeters to get water out of these substrates at that water content. Now this is about the amount of suction that you apply on a soda straw when you’re drinking your coke. That 30% water content, the water potential of the rock wool, has dropped to minus 15 centimeters. So to match that suction, your drink would— the level of your drink would have to drop by five centimeters or two inches. You wouldn’t even notice that change in suction. The plant wouldn’t either. On the other hand, the coco water potential drops to minus 230 centimeters at 30% water content. That’s seven and a half feet. I think you would notice if you had to drink your coke through a seven and a half foot vertical straw. And the plant likely would notice too if it had to suck that much harder to get the water out.

Now before we go on, let’s look at how the availability of water affects plants. Little over 100 years ago, Lyman Briggs and Homer Shantz did some experiments to define the lower limit of available water in soil. They grew sunflowers in small containers and withheld water until the plants wilted and wouldn’t regain turgor placed in a humid environment overnight. They called the soil water content at this point, the permanent wilting water content. Later this equipment became available to measure the water potential of soil. It was found that this permanent wilting water content correlated well with water content of soil at a matric potential of minus 1500 kilopascals and that became known as the permanent wilting point. I want you to note that plants don’t die at that point; they just wilt. Species differ in their actual lower limit of available water, but the minus 1500 kilopascal permanent wilting point still serves as nominal lower limit for available water. Now, there are a couple of other things that we shotuld keep in mind. One is that the water potential in the plant is never higher, and generally is lower, than in the soil because has to be for water to move through the plant. Processes we care about the plant are cell expansion, cell growth, and photosynthesis. We can imagine those being affected by water potential according to the two functions shown in the graph, grow with their cell expansion starts being affected first, the potentials around minus 100 kilopascals. Simulation or photosynthesis starts to be affected around minus 1000 kilopascals. Now these are leaf water potentials but they’re affected by the availability of water from the substrate. So now let’s combine these facts from plant physiology with the moisture retention curves we talked about earlier. The graph shows the permanent wilting point as the vertical red line at minus 15,000 centimeters or minus 1500 kilopascals. The region in the box is the range of potentials, where growth and then assimilation are affected. Growth first and then, as it gets drier, assimilation. If we look at the silt loam, first, its water content is still 25% when growth starts to be affected, and its 12% when it reaches the permanent wilting point. In other words, there’s still a lot of water in the soil when the plant wilts. Our usual way of knowing when to water is to watch the plant for signs of stress. When we see those, we water the plant. With soil, there’s still plenty of water in the soil when these signs become evident. Now if we look at the rock wool, essentially all of its water is gone before we get even close to the matric potential that would start to do stress. If we wait for indications of stress in the plant before we water the rock wool, the plant likely will die. Coco and other soilless substrates are in between. We’d have more water than in the rock wool, when stress symptoms were evident, but there wouldn’t be much margin for error. So one consequence of using these substrates with large pores and narrow pore size distribution is that essentially all of the water they hold is readily available. We control the water content at 20% or 80%. The plant can’t tell the difference. Reducing water content will concentrate solutes, decreasing osmotic potential but matric potential won’t change enough to matter to the plant. Another consequence is that the usual methods for determining when to water by monitoring plant stress won’t work. With soilless substrates, we need to carefully monitor the substrate water content. Now another consequence of large pores and narrow pore size distribution of the soilless substrates is the way water flows in them. Rock wool is the extreme member. But all the substrates used in controlled environments have these limitations. The pictures here show infiltration from a dripper in a clay, a loam, and a sand. The matric forces cause water to move out in all directions, but gravity just pulls the water downward. In the finer material like the clay, the matric forces are stronger than the gravitational forces, and the water moves out in roughly spherical shape. But in the sand, the gravitational forces predominate, and the water mainly moves down. The rock wool is a more extreme example even than sand. And so, the tendency would be for the water to channel directly down the bottom without spreading and filling the full volume of the rock wool. This can be mitigated by keeping the substrate from drying too much and keeping the water content low during the irrigation. We irrigate therefore, irrigate in shots, so you give a shot that amounts to a few percent of the volume of the water that it can hold, and then a rest a period to allow the water to move out into the substrate. It’s also important to carefully consider the position of the dripper and the drains in the rock wool so that the water can’t just channeled through. Another consequence of the large pores is the spatial distribution of water in the substrate. Now already mentioned gravitational forces are much stronger than matric forces in these core substrates. This diagram shows the equilibrium distribution with height of water in rock wool and coco, if we displace the base of it in water. The important thing to learn from this is that the spatial variation of water content in these substrates can be large. And so we have to standardize the monitoring location and be careful to put sensors in the right place every time or our monitoring won’t be good. Also, when we do calculations we need to remember that what we know from a sensor is the water content at a particular spot, not the average water content of the block. One of the jobs to do for the substrate is to supply oxygen to the roots. Low oxygen in the root zone will interfere with water and nutrient uptake and reduce overall plant growth. It’ll also make plants more susceptible to root pathogens. Oxygen moves in soil and soilless substrates by diffusion, and therefore is dependent on on the pore space. Now the graph shows the relative diffusion rate of oxygen in these different substrates at different water contents. If we look at water content of the silt loam, the coco, and the rock wool, say at 40% water, you can see that the oxygen diffusion rate in the rock wool would be more than four times as high as it would be in the silt loam.

Now I hope you have a clearer idea of how different substrates do their jobs of storing water and supplying water to plants. To make this useful for managing water in controlled environment crops, we need a way to measure the water in the substrate. That’s something METER is well qualified to do. The company started almost 40 years ago with an instrument that measured soil moisture. For the past 20 years we’ve been developing and marketing dielectric soil moisture sensors. We have over half a million of those in the field to date. The TEROS 12 that I show on the top left, is our top of the line sensor. It measures dielectric permittivity, bulk electrical conductivity and temperature. And these are the measurements that we need to determine the water and salt content of the growth medium. The TEROS 12 plugs into the AROYA nose shown in the left picture, makes it a part of a wireless mesh network that funnels data from all over the controlled environment facility to a gateway where it can be transmitted to the cloud. AROYA is the name of METER sensing and data management system for a controlled environment applications. The bottom picture shows how the sensor is typically installed. You can see a top view of a rock wool slab with two rock wool blocks on top, the nose sits on top of the slab, and the TEROS 12 plugs into the side of the slab between the blocks and halfway up the slab. The TEROS 12 sensor that you sea at the bottom right has three pins. Dielectric is measured between the right two pins and the electrical conductivity between the left two. The table above that, above the picture, shows the dielectric permittivity of the constituents and see that air has dielectric of one, the mineral organic portion three to five, and water eighty. And so the dielectric signal is by far most strongly affected by the water. But it’s also affected to some extent by the other factors as well. And so correctly converting that signal to water content requires that we know the relationship between dielectric and water content for that specific medium. METER has soil physicists on staff with extensive knowledge of how these sensors work and how to accurately determine water content from dielectric.

Now here’s an example of a full crop cycle in a commercial controlled environment facility. The blue lines, this shows 10 sensors each in a single growth room. The blue lines represent water content of the substrate. The yellow lines represent pore water electrical conductivity. The substrate here is rock wool. So as we pointed out before the actual water content has no direct effect on water availability of the plant. It has a lot to do though with the osmotic potential that can dramatically affect water availability. On this record, you can see how the manager skillfully modulated the electrical conductivity values to match the plants’ needs at each growth phase—those are the lines in yellow—by changing the pattern of water application, amounts, and times. Now try to imagine doing that careful steering, without feedback from the AROYA monitoring system. think it would be like trying to drive a car through an obstacle course with a blindfold on.

Now in this upper graph, I show just a single record from that set of records that we saw on the last slide. The lower graph is an expanded view of just one week of those data. The green line is a record of the light sensor that’s below the canopy. And so you can see early on in the crop cycle, when there isn’t much canopy, the light’s high and then later on the light decreases as the canopy develops. The lights are on for half the day and off for half. The purple line is air temperature and it doesn’t appear that in this facility, they were making much attempt to control that. The blue line is water content. And you can certainly see the patterns in that. Starts out high during the vegetative growth and drops to increase osmotic potential during flower, increases, increases again to lower the osmotic potential during the bulking, and then increases in daily range during maturation. If you look at the daily pattern, in the lower graph, you can see the kind of stair steps as it wets up each day in response to the individual irrigation shots, as the substrate recharges, and then maintains height through the day. The slope of the line here is an indication of the transpiration rate. Pore water electrical conductivity is in red, that responds to the adjustments that are made in the water content. As I mentioned already, we intend to cover that in a lot more detail in the next lecture. So let’s draw some conclusions from the things I’ve presented here. We started out with the idea that we buy a horticultural substrate, that when we do that, we hire it to do several jobs. It needs to hold up the plant, needs to supply the roots with water and nutrients and oxygen. In order to understand how to make the substrate do those jobs, we need to understand how water is held in porous media and how and why it moves. We learned that the large pores and narrow pore size distributions of these substrates impose limits on how they can be successful to use. We want to avoid channeling, maximize the uniformity of water distribution, and make sure oxygen supplies are adequate. To manage these substrates correctly we need to make and display appropriate measurements to give accurate feedback on the consequences of our irrigation decisions. Thank you for being with us today. We hope these ideas will be useful to you in managing irrigation and controlled environment crops.

Alright, thanks Gaylon. Alright, so we’d like to use the next 10 minutes or so to take some questions. And thank you again, for everybody who’s sent in questions already. Looks like we have several that have come in, and there’s still plenty of time to submit your questions. We’ll try to get to as many as we can before we finish. I just want to give you a heads up that if we do not get to your question, or if we only touch on part of your question, we do have them recorded, and someone from our METER Environment team will be able to get back to you via email to answer your question directly. So don’t worry, if we don’t get to your question, submit any and all. And we will try to, again get to as many as we can before we finish. All right. Let’s see Gaylon. This first question is asking about water content predictions here. So in your opinion, what would you say is the best or most accurate or method for predicting soil water content and other soil health hydraulic properties from soil particle distribution.

Now, that’s a little bit outside what we covered here, but there are, they call those pedotransfer functions, the relationship between the soil and hydraulic properties. And there are a number of publications that relate to that. It’s an ongoing area in soil physics and we I mean, I could give some references, but it’s a bigger subject than we can take out here.

Alright. There’s another concern here that maybe you could touch on. So talking about all these substrates that you’ve mentioned, they do retain a lot of water, but if permanent wilting point is high, the plant has a hard time absorbing the water even though the substrate has a lot of retained water. Can you speak to that a little bit?

Well, in soils, normal soils, the something like that silt loam that we talked about here, about half of the total volume is pore space, the soil is saturated. Oh, when the soil is saturated, why it has water content about 50%. When it reaches the field, what we call the field capacity, the amount of water that it normally would retain after an irrigation, is at about 25%. And at permanent wilting point, it’s about 12%. And so half of the water that it normally holds is held too tightly for plants to be able to get it out. There rock wool is clear the other way, but I mean, its field capacity is. Yes, it depends on the condition that we have it in, it’s a little hard to say what it’s field capacity is. But essentially all of the water that’s in it is readily available to the plant.

All right. There’s actually a couple of questions here that I’m going to kind of combine, talking about about rock wool. And since you know, the particle size distribution in rock wool was so narrow, is there any way to steer your crop or to you know, monitor—or not monitor but change the stress of the plant while growing in rock wool?

You know, you can’t, I mean crop steering has to do with any environmental variable that you use to give cues to the plant to change its developmental processes. And one of the things that you do, that you can do for crop steering is to stress the plant, water stress the plant at certain phases in its development. And we’ll talk more about that in the next lecture. But clearly, with these substrates with the large pores like we’ve talked about here, you’re not going to be able to do that with matrix stress, but you can do it with osmotic stress. And we’ll talk about how to do that in the next lecture.

All right. Let’s see here. Got a couple other ones. How about if— here’s another rock wool question. If, yeah, along, I guess, kind of along those similar lines, if all the water tends to drain to the bottom of the rock wool is it better to maintain a lower water content, just to make sure that, you know, oxygen can get to the roots, and does that then make it more difficult to manage water content effectively, since you know that drop might look a bit scary?

Well, this gets back to one of the graphs that I showed, the distribution of water content in a rock wool slab. And certainly, you need to manage that very carefully so that you have sufficient oxygen and also sufficient water for the plant. And so a lot of that comes down to where you place the sensor and where you place the drain holes and where you place the dripper. But the idea is to maintain all of that volume of rock wool so that the water is available enough for plants to take it out. But to maintain most of it, in a well aerated state so that the oxygen is readily available too.

So another, and there’s a couple other questions that are asking this, but you touched on this a little bit about where to place sensors and what the sensors are measuring, what is their, you know, range, but how can they deal with spatial variability in soil properties, or at least in these within these substrates here?

The key is to find and know the place to monitor that gives you the best picture of the whole system. And that’s something that we’ve spent a lot of time here trying to work out. Again, it’s more detail than we have time to go over here. But when we set up an AROYA system, why people have worked that out so that we can give advice on where to place the sensors to give the best picture of what’s going on in the substrateT.

Alright, looks like we might have time for one more question here. There are a couple of questions in here that are asking about about perlite, about sensors, how well do sensors work in perlite? It’s comparison to rock wool, do you have any insight on using perlite and monitoring soil moisture within or water content or other things with with perlite?

You know, I think there’s no problem with monitoring in perlite, the calibration, the relationship between dielectric and water content probably is not the same for perlite as it is for rock wool or for mineral soil. But that’s easily determined. And again, METER can give advice on that or as the AROYA system is put into place.

All right. Great. Thank you again, Gaylon. And thanks to everyone who’s joined us today. That’s going to wrap it up for us. We hope you enjoyed this discussion. And thank you again for such great questions. We did get quite a few questions that we did not get to. Again, somebody will be able to get back to you from our METER Environment team to answer your question directly with that email that you registered with. Also, please consider answering the short survey that will appear after this webinar is finished, just to tell us what types of webinars you’d like to see in the future. And for more information on what you’ve seen today, please visit us at Finally, look for the recording of today’s presentation in your email. And stay tuned for future METER webinars. Thanks again. Stay safe and have a great day.

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