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’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
Irrigation management: Why it’s easier than you think
Years ago, we received an irrigation management call from a couple of scientists, Drs. Bryan Hopkins and Neil Hansen, about the sports turfgrass they were growing in cooperation with the Certified Sports Field Managers at Brigham Young University (BYU) and their turfgrass research and education programs. They wanted to optimize performance through challenging situations, such as irrigation controller failure and more. Together, we began intensively examining the water in the root zone.
As we gathered irrigation and performance data over time, we discovered new critical best practices for managing irrigation in turfgrass and other crops, including measuring “soil water potential”. We combined soil water potential sensors with traditional soil water content sensors to reduce the effort it took to keep the grass performance high, while saving water costs and reducing disease potential and poor aeration. We also reduced fertilization costs by minimizing leaching losses out of the root zone due to overwatering.
Supercharge yield, quality and profit in any crop with soil moisture-led irrigation management
This article uses turfgrass and potatoes to show how to irrigate using both water potential and water content sensors, but these best practices apply to any type of crop grown by irrigation scientists, agronomists, crop consultants, outdoor growers, or greenhouse growers. By adding water potential sensors to his water content sensors, one Idaho potato grower cut his water use by 38%. This reduced his cost of water (pumping costs) per 100 lbs. of potatoes, saving him $13,000 in one year.But that’s not even the best part. His yield increased by 8% and he improved his crop quality—the rot he typically sees virtually disappeared.
What is soil water potential?
In simple terms, soil water potential is a measure of the energy state of water in the soil. It has a complicated scientific definition, but you don’t have to understand what soil water potential is to use it effectively. Think of it as a type of plant thermometer that indicates “plant comfort”—just as a human thermometer indicates human comfort (and health). Here’s an analogy that explains the concept of soil water potential in terms of optimizing irrigation.
The environment plays a large role in any plant study. Ensuring you’re capturing weather and other environmental parameters in the best way allows you to draw better conclusions. To accurately assess plant stress tolerance, you must first characterize all environmental stressors. And you can’t do that if you’re only looking at above-ground weather data.
For example, drought studies are notoriously difficult to replicate and quantify. Knowing what kind of soil moisture data to capture can help you quantify drought, allowing you to accurately compare data from different years and sites.
Get better, more accurate conclusions
It’s important for your environmental data to accurately represent the environment of your site. That means not only capturing the right parameters but choosing the right tools to capture them. In this 30-minute webinar, application expert Holly Lane discusses how to improve your current data and what data you may not be collecting that will optimize and improve the quality of your plant study. Find out:
How to know if you’re asking the right questions
Are you using the right atmospheric measurements? And are you measuring weather in the right location?
Which type of soil moisture data is right for the goals of your research or variety trial
How to improve your drought study, why precipitation data is not enough, and why you don’t need to be a soil scientist to leverage soil data
How to use soil water potential
How accurate your equipment should be for good estimates
Key concepts to keep in mind when designing a plant study in the field
What ancillary data you should be collecting to achieve your goals
Holly Lane has a BS in agricultural biotechnology from Washington State University and an MS in plant breeding from Texas A&M, where she focused on phenomics work in maize. She has a broad range of experience with both fundamental and applied research in agriculture and worked in both the public and private sectors on sustainability and science advocacy projects. Through the tri-societies, she advocated for agricultural research funding in DC. Currently, Holly is an application expert and inside sales consultant with METER Environment.
Mismanagement of salt applied during irrigation ultimately reduces production—drastically in many cases. Irrigating incorrectly also increases water cost and the energy used to apply it.
Understanding the salt balance in the soil and knowing the leaching fraction, or the amount of extra irrigation water that must be applied to maintain acceptable root zone salinity is critical to every irrigation manager’s success. Yet monitoring soil salinity is often poorly understood.
Measure EC for consistently high crop yields
In this webinar, world-renowned soil physicist Dr. Gaylon Campbell teaches the fundamentals of measuring soil electrical conductivity (EC) and how to use a tool that few people think about—but is absolutely essential for maintaining crop yield and profit. Learn:
The sources of salt in irrigated agriculture
How and why salt affects plants
How salt in soil is measured
How common measurements are related to the amount of salt in soil
How salt affects various plant species
How to perform the calculations needed to know how much water to apply for a given water quality
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.
Charles Bauers has been a hydroponic snapdragon grower for 17 years. He knows—in detail—how to produce a good snap. But five years ago, he needed a better way to measure water.
“We had no quantitative way to measure water. That was the limiting factor for me,” he explains. Other inputs, like fertilizer, were quantifiable, but Bauers still depended on “gut feel” for watering, and no matter how quickly he reacted to changes in the crop, he couldn’t consistently produce grade-one snapdragons.
He wanted a scale, a “recipe of numbers” that would let him produce a good crop all the time in all sections of the greenhouse.
“There are always areas that seem to produce good quality flowers, and then there are areas that are a bit more of a challenge. I installed METER soil moisture sensors in the good areas and the stressed areas and compared the two. Then I worked my stressed areas up to the same numbers.”
Snapdragons are very sensitive to moisture stress. “It’s a ten-week crop. If you don’t get the moisture right in the first two weeks, you can compromise that crop.”
Identifying irrigation set points
The soil moisture sensors made a huge difference in Bauers’s ability to get the moisture right. “They give me, targeted set points that I can shoot for all the time, and if I hit the targeted set point, I know I’m going to have good quality snaps, barring any other type of stress.
Grade-one snapdragons are worth 40% more than grade twos, and the difference between the two is created by “incipient stress—water stress that you can’t measure with your fingers. You can’t see it, you can’t feel it, it’s stress at the root. There’s a difference between a 28% vwc [volumetric water content] and a 23% vwc. It’s only 5%, but one produces grade ones and one produces grade twos.”
Empowered with real-time information
Moisture sensors gave Bauers real-time information that helped him get the watering right in every part of the greenhouse. “I became more consistent because I had a number to go at. Because we’re a hydroponic crop, we see the effects real quick, and I’d say ‘I just have to add a little more water here.’ But [before the sensors,] invariably we had areas that were stressed because you really never knew when you had enough water on that crop. With sensors, you can consistently put the right amount of water on all the time.”
Bauers quickly became adept at using sensors to address his irrigation challenges. The sensors showed him where his irrigation system was broken or underperforming, helped him identify problems like a root growing into a drip tube, or an unplugged dripper. But as the sensors became part of his routine, he was surprised to discover a new opportunity.
“Besides giving me the real-time information, the sensors gave me the ability to look at trends…over a week or a month and be proactive if we started moving away from our set point. We could add more water, set shorter run times, or just make some changes in the irrigation system to get more in line with the set points. That was one of my biggest surprises, how well we were able to be proactive toward environmental changes using the trending of the charts. That was a bonus.”
Reducing production and labor costs
After five years of daily monitoring, Bauers is now ready to go to an even higher level. “The next huge area we see sensors in is as big, or bigger, than the actual growing of the plant itself. We’re going to use these sensors to guide us as we strip out all excess production costs, and that’s happening today. As an example, over the next five months we’ll be trimming our substrate use by 85%. Not only do we save on materials, but if you have 85% less substrate to work with or move, you reduce labor costs.”
In fact, the sensors have become an integral part of how Bauers does business. I asked him how he would feel if he lost them. “My gosh,” he said, “It would be like going back ten years. It would be like trying to measure the temperature in a room without a thermometer. We are totally dependent on them.”
Everybody measures soil water content because it’s easy. But if you’re only measuring water content, you may be blind to what your plants are really experiencing.
Soil moisture is more complex than estimating how much water is used by vegetation and how much needs to be replaced. If you’re thinking about it that way, you’re only seeing half the picture. You’re assuming you know what the right level of water should be—and that’s extremely difficult using only a water content sensor.
Get it right every time
Water content is only one side of a critical two-sided coin. To understand when to water or plant water stress, you need to measure both water content and water potential.
In this 30-minute webinar, METER soil physicist, Dr. Colin Campbell, discusses how and why scientists combine both types of sensors for more accurate insights. Discover:
Why the “right water level” is different for every soil type
Why soil surveys aren’t sufficient to type your soil for full and refill points
Why you can’t know what a water content “percentage” means to growing plants
How assumptions made when only measuring water content can reduce crop yield and quality
Water potential fundamentals
How water potential sensors measure “plant comfort” like a thermometer
Why water potential is the only accurate way to measure drought stress
Why visual cues happen too late to prevent plant-water problems
Case studies that show why both water content and water potential are necessary to understand the condition of soil water in your experiment or crop
Dr. Colin Campbell has been a research scientist at METER for 20 years following his Ph.D. at Texas A&M University in Soil Physics. He is currently serving as Vice President of METER Environment. He is also adjunct faculty with the Dept. of Crop and Soil Sciences at Washington State University where he co-teaches Environmental Biophysics, a class he took over from his father, Gaylon, nearly 20 years ago. Dr. Campbell’s early research focused on field-scale measurements of CO2 and water vapor flux but has shifted toward moisture and heat flow instrumentation for the soil-plant-atmosphere continuum.
Hello, my name is Colin Campbell. I’m a senior research scientist here at METER Group. And today we’ll talk about how to estimate the transpiration from a single leaf. Occasionally we get this question: Can I estimate the transpiration from a leaf by measuring its stomatal conductance? Unfortunately, you can’t. And I want to show you why that’s true and what you’ll need to do to estimate the total conductance, and therefore, the evaporation of a leaf.
The calculation of transpiration (E) from a leaf is given by Equation 1
where gv is the total conductance of vapor from inside the leaf into the air, Cvs is the concentration of vapor inside the leaf and Cva is the concentration of vapor in the air.
Soil moisture data analysis is often straightforward, but it can leave you scratching your head with more questions than answers. There’s no substitute for a little experience when looking at surprising soil moisture behavior.
Understand what’s happening at your site
METER soil scientist, Dr. Colin Campbell has spent nearly 20 years looking at problematic and surprising soil moisture data. In this 30-minute webinar, he discusses what to expect in different soil, environmental, and site situations and how to interpret that data effectively. Learn about:
Telltale sensor behavior in different soil types (coarse vs. fine, clay vs. sand)
Possible causes of smaller than expected changes in water content
Factors that may cause unexpected jumps and drops in the data
What happens to dielectric sensors when soil freezes and other odd phenomena
Surprising situations and how to interpret them
Undiagnosed problems that affect plant-available water or water movement
Why sensors in the same field or same profile don’t agree
Dr. Gaylon Campbell shares his newest insights and explores options for water management beyond soil moisture. Learn the why and how of scheduling irrigation using plant or atmospheric measurements. Understand canopy temperature and its role in detecting water stress in crops. Plus, discover when plant water information is necessary and which measurement(s) to use.
Predictable Yields using Remote and Field Monitoring
New data sources offer tools for growers to optimize production in the field. But the task of implementing them is often difficult. Learn how data from soil and space can work together to make the job of irrigation scheduling easier.
Dr. Colin Campbell, a senior research scientist at METER Group, as well as adjunct faculty at Washington State University teaches about relative humidity.
Watch the video to find out why we use the term relative humidity and why comparing RH at different research sites can be a challenge.
Why is humidity relative?
Hi, I’m Dr. Colin Campbell. I’m a senior research scientist here at METER Group, as well as adjunct faculty up at Washington State University. And I teach a class in environmental biophysics. And today, we’re going to be talking about relative humidity. Have you ever looked at a weather report and wondered, what do they mean by the term relative? Why aren’t we talking about absolute things? And so today I’m going to talk about what is relative humidity? Well, relative humidity we’re going to define here as just hr. And hr is equal to the partial pressure of water vapor in air divided by the saturation vapor pressure or the maximum possible partial pressure of water in air as a function of temperature. So this is relative because anytime we have a partial pressure of water vapor, we’re always dividing it by the maximum possible water vapor that could be in the air at any point.
Comparing RH at different sites is a challenge
So, why would relative humidity be such a challenge for us as scientists to use in comparing different sites? I wanted to talk about that so we can focus in here on this saturation vapor pressure. Over here we have Tetens equation. This says that the saturation vapor pressure, which is a function of air temperature is equal to 0.611 kPa times the exponential of a constant “b” times the air temperature divided by another constant “c” plus the air temperature. So at any point, depending on the air temperature, we can calculate the saturation vapor pressure, and then we can put it back into this equation and get our relative humidity. There are two situations we might think about for calculating our saturation vapor pressure. The most typical is this one: where that constant “b” is 17.502 degrees C. And the constant “c” is 240.97 degrees C (the units on this are degrees C, so these will cancel). If we’re over ice, those constants will be different: “b” would be 21.87 degrees C and “c” would be 265.5 degrees C.
So as I mentioned, relative humidity is a challenging variable to use in research because while vapor pressure (ea) (the vapor pressure of the air) is somewhat conservative across a day, the saturation vapor pressure (with respect to air temperature), this changes slowly with temperature across the day. So if we graphed temperature on one axis and the relative humidity on the other axis, we might during a typical day have a temperature range that looks somewhat like this. And even if the actual vapor pressure “ea” wasn’t changing, we’d see a relative humidity trend that looked like this: only changing because of air temperature. And because of that, if we wondered how do I compare the water in the air at one research site, for example, with the water in the air at another research site? We might be inclined to average them. But because of this trend, the average of the relative humidity at any site tends to be around 0.60 to 0.65 and therefore will be totally irrelevant in the literature.
So we need to speak in absolutes, and in my next lecture, I’m going to go into what we can do to calculate that absolute relative humidity. If you want to know more about making measurements in the atmosphere, go to metergroup.com, look at our atmospheric instrumentation, and you can learn more from there.