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Posts from the ‘Greenhouse’ Category

Chalk talk: How to model air temperature variation with height

In his latest chalk talk, Dr. Colin Campbell, environmental scientist at METER Group, teaches how to model vertical variation in temperature and how to estimate sensible heat flux.

Video transcript

Hello, everyone. My name is Dr. Colin Campbell, and I’m a senior research scientist here at METER Group. For today’s chalk talk, we’ll be talking about modeling vertical variation in temperature. In Figure 1, I’ve put together a graph that shows the maximum and minimum temperature with height and depth in the soil at some snapshot in time at a particular place. 

Figure 1. Maximum and minimum temperature with height and depth at a snapshot in time, in a particular place

It’s interesting to note that the change in temperature with depth in the soil is much faster than the change in temperature with height, whether we’re talking about a maximum or minimum. And the reason is that even though air is a good insulator, it also mixes really well. And that mixing is caused by eddies. And there’s a little more to that story. It depends specifically on surface heating by the sun through radiation and the cover type, whether it’s plants, rocks, boulders, straight soil, snow, or wind.

Equation 1

If we were going to model that, we would start by writing an equation (Equation 1) where a temperature at sun height, Z, above the surface (see variables noted in Figure 1), is equal to an aerodynamic surface temperature, T0, minus the sensible heat flux, divided by 0.4 times rho, CP, which is the volume specific heat of the air, times a variable called u*, which is the friction velocity. We multiply all that by the logarithm of z, the height above the surface minus d, which is the zero plane displacement, divided by z h, which is a roughness parameter. You might notice up here in the list of variables, that the zero plane displacement is 0.6 times H. H is the canopy height in meters. The rough roughness parameter can be estimated as 0.02 times the canopy height or times H. Now we have an equation that will help us model temperature with height. 

However, often we don’t know things like H, our sensible heat flux, and u*, our friction velocity. One of the things that we notice about this equation is that it’s set up somewhat like a linear equation. As you know, an example of a linear equation is something like Equation 2.

Equation 2

Figure 1 isn’t written quite that way, but if we look closely at the example below (Equation 3), this value could be our b, and this value our m, and this value could be our x. And if we do that, we actually can get some use out of graphing temperature with height. 

Equation 3

So we went out one day and measured this with a METER Group set of environmental sensors set up at certain heights above the surface. Here we placed sensors at 0.2 m, 0.4 m, 0.8 m, and 1.6 m above the ground. 

Table 1

To visualize this, in Figure 2 we graphed height on the y axis and temperature on the x axis, similar to the graph in Figure 1.

Figure 2. Graph showing the relationship between height and temperature

We know from Equation 1 that the axes for temperature and height should be switched because temperature is the dependent variable, and height is the independent variable. So if we switch axes it would look like the graph in Figure 3.

Figure 3. Graph showing the relationship between height and temperature where temperature is the dependent variable and height is the independent variable.

Figure 3 is graphed with the independent variable on the x axis and height on the y axis. If we fit this curve with today’s calculators, it would be fairly easy to get a curve that would fit that. But since it’s a linear equation, we can take the temperature data from Table 1 and the In ((Z-d)/ZH) data from Table 1 and graph them together.

Figure 4. Relationship between temperature and In Z-d/zh

Figure 4 is a graph that shows what happens when we do that. Notice that, just like we suggested, it creates a linear equation (Equation 4). 

Equation 4

We learned in Figure 1 the B value was equal to t0 (our aerodynamic surface temperature). Since we know our surface temperature is 34.5 degrees, we can estimate what the temperature is down here at the surface, even though we only measured down 0.2 m. 

We also know from Equation 4 that our M value is equal to -2.01. And if we look at Equation 1, our slope value is below.

Equation 5 (the slope value from Equation 1)

So we can write

Equation 6

How to estimate sensible heat flux

Now, if we were interested in the sensible heat flux, which we often are, we can simply rearrange this equation to be

Equation 7

And in Figure 1, I forgot to give you this value, but for an air temperature of 20 degrees celsius, 

Equation 8

And then finally, a typical unit for friction velocity, which should be measured in the field over the specific canopy you are in, is about 0.2 meters per second.

Equation 9

So if we did this calculation, we would learned that there’s about 193 watts per meter squared of sensible heat flux coming off that surface. 

Equation 10

So if we can measure temperature at a few heights, we can estimate what the heat flux is coming off the surface assuming we know something about our canopy. Learn more about measuring and modeling environmental parameters at metergroup.com/environment. If you have any questions feel free to email Dr. Campbell at [email protected].

Learn more

Read about weather station best practices—>

Discover the ATMOS 41 All-In-One Weather Station—>

Download the Researcher’s complete guide to soil moisture—>

Water Potential 101: What It Is. Why You Need It. How To Use It.

Soil is no longer a black box 

Advances in sensor technology and software now make it easy to understand what’s happening in your soil, but don’t get stuck thinking that only measuring soil water content will tell you what you need to know.

Water content is only one side of a critical two-sided coin. To understand when to water, plant-water stress, or how to characterize drought, you also need to measure water potential. 

Better data. Better answers.

Soil water potential is a crucial measurement for optimizing yield and stewarding the environment because it’s a direct indicator of the availability of water for biological processes. If you’re not measuring it, you’re likely getting the wrong answer to your soil moisture questions. Water potential can also help you predict if soil water will move, and where it’s going to go. Join METER soil physicist, Dr. Doug Cobos, as he teaches the basics of this critical measurement. Learn:

  • What is water potential?
  • Why water potential isn’t as confusing as it’s made out to be
  • Common misconceptions about soil water content and water potential
  • Why water potential is important to you

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Presenter

Dr. Cobos is a Research Scientist and the Director of Research and Development at METER.  He also holds an adjunct appointment in the Department of Crop and Soil Sciences at Washington State University where he co-teaches Environmental Biophysics.  Doug’s Masters Degree from Texas A&M and Ph.D. from the University of Minnesota focused on field-scale fluxes of CO2 and mercury, respectively.  Doug was hired at METER to be the Lead Engineer in charge of designing the Thermal and Electrical Conductivity Probe (TECP) that flew to Mars aboard NASA’s 2008 Phoenix Scout Lander.  His current research is centered on instrumentation development for soil and plant sciences.

Episode 9: Pioneers of Environmental Measurement

What was the life of a scientist like before modern measurement techniques? In our latest podcast, Campbell Scientific’s Ed Swiatek and METER’s Dr. Gaylon Campbell discuss their association with three pioneers of environmental measurement.

Learn what it was like to practice science on the cutting edge. Discover the creative lengths they went to and what crazy things they cobbled together to get the measurements they needed.

Listen now—>

Webinar Series: Irrigation of Controlled Environment Crops for Increased Quality and Yield

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 the 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

Watch it now—>

The complete guide to irrigation management using soil moisture

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. 

BYU researchers are zeroing in on irrigation management best practices leading to better outcomes that are easier to achieve.

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. 

Read more—>

Improve Your Plant Study: 3 Types of Environmental Data You May Be Missing

What data are you missing?

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

Register now—>

Presenter

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.

Soil Moisture Sensors Aid Crop Production in Space

If you’re an astronaut on an exploration Mission to Mars, lack of breathable oxygen isn’t the only challenge you’re facing. There’s another issue that can heavily impact your performance: lack of veggies.

Mars

It turns out the astronaut food system must be supplemented with fresh crops during long-term exploration missions. NASA has identified that vitamins and antioxidants degrade over time and is now funding research on the best way to grow fresh vegetables in space to supplement astronaut nutrition.

How well do plants grow in space?

Researchers including Dr. Oscar Monje, research scientist at NASA’s Kennedy Space Center in Florida, are studying the best materials and methods for growing vegetables in space. Monje says, “Growing plants in a space station is challenging because both space and power are limited. All the plant chambers built in the past 40 years focused on enabling space biology studies that centered on how to grow plants in space. They wanted to know the effects of growing in zero gravity. Can plants grow normally? Are they stressed? Can they produce seeds? But now we want to focus on space crop production. We want to supplement astronauts’ diets with essential minerals and vitamins during long duration missions.”

Kennedy Space Center

Early growing experiments in the BPS

Monje was a student of Dr. Bruce Bugbee at Utah State University who studies plants in space for bioregenerative life support systems. After graduating and doing a postdoc at the Space Dynamics lab, he started at Kennedy in 1998 researching how to grow wheat in space in the PESTO (Photosynthesis Experiment and System Testing Operations) Experiment. Dr. Gary Stutte, the principal investigator and Dr. Monje grew wheat in the Biomass Production System (BPS), a four chamber system that consumed 280 W of power. The BPS was used to measure photosynthesis, demonstrating plant harvests, priming pre-planted root modules, pollinating plants, as well as collecting gas and liquid samples.

Monje says, “Back then, all experiments were shuttle experiments (7-11 days at a time). The PESTO Experiment flew for 73 days in space and was essentially several shuttle missions conducted back to back. We measured root zone moisture with a pressure sensor monitoring root module matric potential. We learned that as long as you provide plants with adequate root zone aeration, good soil moisture, and the right light and CO2, they grow normally with no visible plant stress—just like on earth. The BPS was a precursor of the Advanced Plant Habitat (APH) facility on the International Space Station plant, an environmentally controlled growth chamber designed for conducting both fundamental and applied plant research for experiments lasting as long as 135 days.

New growth chambers introduced

The BPS was very complex, but the chambers were small and the light level was moderate. Ten years ago, NASA developed two large area (0.2 square meter) crop production systems to grow fresh salad crops in substrate-based media for the astronauts: the “Veggie” and the “APH”. Monje says, “Veggie is open to the cabin so there is no environmental control of CO2 or temperature, and it is watered by the crew. The light level provided by red, blue and green LEDs is moderate and the environment is not monitored. However, it grows lettuce crops that are safe to eat by the crew. The Advanced Plant Habitat on the other hand, is a Cadillac compared to the Veggie. With the APH you can load experiment profiles from the ground that control the light level (up to 1000 umol/m2s, half-full sunlight), the spectral quality, the CO2 concentration (up to 5000 ppm), photoperiod of light, and root zone moisture. The APH can be monitored in near-real time with minimal crew intervention for weeks at a time. To date, it has been used to grow wheat, Arabidopsis, and radish crops during space biology and crop production experiments”

The APH has been used to grow wheat, Arobidopsis, and radish crops

Measuring root zone moisture in space

Monje says that the 5-cm tall APH root zone is divided into four independently controlled root modules, called quadrants. In each quadrant, media moisture is controlled based on matric potential using a pressure sensor. However, the matric potential measured by the pressure sensor does not capture vertical variation in volumetric moisture. He says, “Each quadrant is watered with a porous tube system that distributes water throughout the porous media (arcillite) that is mixed with slow release fertilizer. In the 5-cm tall root zone at one g, most of the water is ponded at the bottom, and the top layer of media where the plants are germinating can become too dry. For these reasons, two small, rugged volumetric EC-5 moisture sensors were added to each quadrant to monitor moisture redistribution phenomena in microgravity. These sensors are insensitive to salinity and temperature effects. Thus, APH uses eight volumetric moisture sensors, two in each quadrant (one high, one low) to monitor root zone moisture. When watering in space, moisture redistribution occurs because capillary forces in microgravity distribute water evenly across the substrate and affect aeration. Even though the sensors are at different heights, they can read the same, as opposed to one flooded and the other one drier.”

Monje adds that, “Balancing the mix of aeration with enough water in a microgravity environment is the crux of the problem. If you don’t water plants enough, they don’t grow fast enough, but if you give them too much water, then you inhibit O2  supply to roots and nutrient uptake. So we’re using volumetric water content sensors in the APH root module at different levels to control the moisture. The sensors are like our ‘fingers in the soil’.”

What’s next?

Monje says the next step is to develop novel watering systems that do not use granular media.  He says, “Each APH root module holds about six kilograms of arcillite media, which is used only once per crop. Similarly, Veggie uses nearly two kilograms of media distributed into six independently watered root modules. Although these root modules grow normal plants in space biology experiments, this approach is not sustainable for crop production as transporting this much mass all the way to Mars is not going to be feasible.”

Deploying experiments on the moon can be challenging

Monje believes that getting these crop growth systems ready for a trip to Mars may take a while. He says right now, the Moon is a new proving ground for these technologies as part of the Artemis program, and deploying experiments on the Moon brings new challenges too. He adds, “An interesting thing about the Moon is you have partial gravity. It’s not one g. It’s 1/6 g. Plus, you have the issue of space radiation, and temperature must be controlled, unless you deploy your experiment in a manned habitat. From a biology point of view, we want to understand how plants will respond to growing in high radiation and partial gravity environments.”

Monje says it’s been an incredible journey to work on this type of research for many years. He laughs, “Since 1998, I’ve been pinching myself every day because this work is so challenging and yet so much fun. It’s pretty amazing.”

Learn more about measuring soil moisture

Download the Researcher’s Complete Guide to Soil Moisture—>

Soil Electrical Conductivity: Managing Salts for Sustained High Yields

Managing salts: Why you should care more

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

Register now—>

Presenter

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.

Learn more

Download the “Complete guide to irrigation management”—>

Snapdragons and soil moisture sensors

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.

Soil sensors optimize irrigation for improved quality and profit

“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.”

The TEROS 12 is well-suited for greenhouse applications

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.”

Soil sensors helped identify and prevent irrigation problems

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.”

Learn more

Watch: How to improve irrigation scheduling using soil moisture—>

See all irrigation webinars—>

Download the “Complete guide to irrigation management”—>

Webinar: Why Water Content Can’t Tell You Everything You Need to Know

Water content can leave you in the dark

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.

TEROS 21 water potential sensor

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

WATCH IT NOW—>

Presenter

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.

Learn more

Download the “Complete guide to irrigation management”—>