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Measuring Water Potential in Concrete

Trevor Dragon, a former METER Research and Development Engineer, was pouring concrete at his Beeville, Texas, farm one day and wondered if he could measure moisture in concrete with a matric potential sensor instead of the more traditionally used volumetric water content sensor (VWC) to get more accurate readings.  Dragon says, “We had about five concrete trucks come in that day, and we poured five different slabs.  Every truck had a different amount of water added.  One particular batch of concrete was really wet and soupy, and I became curious to measure it and compare it to the other slabs.”

Concrete slab drying down at Trevor's Texas farm.

Concrete slab drying down at Trevor’s Texas farm.

Why Measure Moisture in Concrete?

As concrete hardens, portland cement reacts with water to form new bonds between the components of the concrete.  This chemical process, known as hydration, gives concrete its characteristic rock-like structure.  Too much or too little water can reduce the strength of the concrete.  Adding excess water can lead to excessive voids in concrete while providing too little water can inhibit the cement hydration reaction. Thus, when you pour a slab in south Texas, where it’s exposed to high wind and intense heat, sufficient water must be added, and precautions must be taken to minimize evaporation of water from the slab surface as the concrete hardens.

Better Readings:

Dragon chose the matric potential sensor because he wondered if it would be more accurate than a VWC measurement.  He says, “I knew that VWC sensors were calibrated for soil, and because of that they would lack accuracy.  But the water potential sensor is calibrated for the ceramic it contains.  I figured it would be closer to the real thing without having to do a custom calibration.”

Moisture in concrete has been difficult to measure because the high electrical conductivity early in the hydration process throws off water content sensor calibration. So, Dragon was surprised when his data turned out to be really good.  He comments, “The dry down curve of the matric potential sensor was a perfect curve. There was a nice knee (drop from saturation) after about 200 minutes, and it just went down from there.  We’re kind of stumped because we are trying to understand why the data came out so well and why the curve looks so good.”  

MPS2 Water Potential in Concrete diagram

Water Potential in Concrete

The scientists at METER sent the drydown curve to Dr. Spencer Guthrie, a civil engineering professor, to see what he thought.  He explains, “I suspect that the concrete is experiencing initial set at around 200 minutes.  This is a very normal time frame by which finishing operations need to be complete.  At this stage in cement hydration, the concrete becomes no longer moldable.  A rigid capillary structure is forming, and individual pores are taking shape.  As hydration continues, the pores become smaller and smaller, which may explain the decrease in matric potential.”

New Methods:

One theory Dragon and his colleague Dr. Colin Campbell came up with was that perhaps Dragon’s unique method of inserting the sensors made a difference in the measurements.  He explains, “The first thing I did was look for the rebar in the concrete, and I placed the sensors in the exact center of one of the squares to avoid the influence of metal on the sensor electromagnetic field.  Also, I didn’t insert the sensors the same way you would insert them into soil.  In soil, you put the sensors in vertically; I placed the water potential sensor horizontally because in this case, I was not interested in how water was moving in the slab but how it was being used over time.

What Does It Mean for the Future?

The behavior of the water potential sensor embedded in the concrete clearly indicated a drying process where water becomes less available over time. However, the implications are still unknown.  Can the quality of the concrete be determined from the speed or extent of water becoming less available?  Hopefully, this opportunistic experiment by Dragon will lead to more tests to show whether this approach is useful to others.  

Dr. Guthrie agrees the idea should be explored further and comments, “The matric potential measurements were not redundant with the water content measurements.  Instead, they offered additional, interesting information about the early hydration characteristics of the concrete.  In the context of construction operations, the water potential data indicated what is normally determined by observing the impression left in the concrete surface from the touch of a finger.  In the context of research, however, the use of a water potential sensor may yield helpful information about how certain admixtures, for example, influence the development of hydration products in concrete over time.

Download the “Researcher’s complete guide to water potential”—>

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The Potential of Drones in Research

Someday soon,  multi-rotors will execute pre-programmed flight paths over several hundred research plots collecting daily data and sending it back to a computer while researchers sip their morning coffee.  Researchers and growers won’t need to know anything about flying: the drones will fly themselves.  This is the dream.

One UAV (unmanned air vehicle) industry leader at the above drone demonstration commented, The truth is that this is where agriculture (and research) is going, and I don’t mean ‘Tomorrowland’ going–I mean it’s pretty much there.  The only thing that’s holding us back is a permit from the FAA for autonomy, and that’s because the FAA is slowly backing into this UAV piece because we have the busiest general aviation sky in the world. But really, what you should have in your mind is multiple units operating with a single operator in a control vehicle.”  The above UAV was extensively tested in California’s NAPA valley with results soon to be published online.

In this blog, a METER scientist and an instrumentation engineer give their perspectives on what needs to happen before drones reach their full research potential.  

Drone hexacopter flying against a blue sky

Drone Hexacopter

What are the advantages of drones for researchers?

Dr. Colin Campbell, research scientist-

One of the biggest challenges of work in the field is variability: low spots, high spots, sandy soil, clay soil, hard pans beneath the surface in some areas and not in others.  This results in highly variable performance in crops.  In addition to that, even when you have good homogeneity in a field, you might have differences due to irrigation or rainfall. If we want to improve agriculture, one thing that we have to do is be able to come out with better tools to be able to visualize the field in more than a single dimension. In order to do this right now, students go out and take plant measurements all day, every day, all summer long. The advantage of a drone is that you could do flyovers of a field, monitoring the traits that you’re interested in using reflectance indices that would normally take days of work.

What are the obstacles to progress?

Greg Kelley, mechanical engineer, and drone hobbyist-   

Recently, the FAA has come out with a set of guidelines for the industrial use of drones:  flying machines have to stay under a certain ceiling (500 ft; 150 m), and they have to be flown in the line of sight of the operator.  The naive thing about those policies is: how much control does the operator have over the drone anyway?  It used to be that with your remote control, you were moving the control surfaces (flaps, rudder, etc) on the aircraft, but this is changing.  The onboard computer performs things like holding a stable altitude, maintaining a GPS location, or auto-stabilization (it keeps the aircraft level, even when a gust of wind comes).  Those are degrees of control that have been taken away from the operator. Thus, according to the level of automation that the operator has built into the system, he may not be in direct control at all times. In fact, these machines are being developed so that they can fly themselves. From my perspective, the FAA regulations are going to have to evolve along with the automation of drones in order to allow the development of this technology in an appropriate way.

Drone with eight rotors sitting on a landing pad

Drone with eight rotors.

What needs to happen before drones reach their full potential?

Dr. Colin Campbell–  

Even if we get the flexibility required with drones, we’ve got to get the right sensor on the drone. On the surface, this seems relatively simple.  Sensors to measure spectral reflectance are available in a package size that should easily mount on a drone platform. But, there are still many challenges.  First, current spectral reflectance sensors make a passive reflectance measurement, meaning we’re at the mercy of the reflected sunlight.  Clouds, sun angle, and leaf orientation, among other things, will all affect the measurement. There are several groups working on this (just search “drone NDVI” on the internet), but it’s a difficult problem to solve.  Second, drones create a spectral reflectance “map” of a field that needs to be geo-referenced to features on the ground to match measurements with position.  Once data are collected, the behavior of “plot A” can only be determined by matching the location and spectral reflectance of “plot A.”  Different from the first challenge, this is more related to programming than science but is still a major hurdle.

Despite these challenges, drones promise incredible benefits as an agricultural and environmental measurement tool. As one industry leader at the drone demonstration put it, “the complexity of the problems that agriculture faces and the opportunities for efficiencies are vast.  It will require ongoing engagement, next year and the year after that. There are a lot of questions to be answered and the efficacy is yet to be determined, but it’s exciting to watch the UAV helicopter and where it’s going.”  Both Campbell and Kelley agree that significant advances will be made within the next few years.

Read about an ROI calculator that’s been created to help growers quantify whether the benefits of using a drone will exceed their costs.

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Great Science Reads: What our Scientists are Reading

We asked our scientists to share the great science reads they’ve perused recently.  Here’s what they’ve been reading:

Open book with Highlighter and Glasses on top of it

Letters to a Young Scientist by E.O. Wilson

Edward Wilson's book "Letters To A Young Scientist"

Steve Garrity: E.O. Wilson is a leader in the science of biology. This book is a simple read. What I like most about it is that it very effectively conveys Dr. Wilson’s passion for science. His thoughts on what it takes to be a successful scientist resonated with me the most.  In describing what it takes to be a successful scientist, E.O. Wilson says that being a genius, having a high IQ, and possessing mathematical fluency are all not enough. Instead, he says that success comes from hard work and finding joy in the processes of discovery. Dr. Wilson gets specific and says that the real key to success is the ability to rapidly perform numerous experiments. “Disturb nature,” he says, “and see if she reveals a secret.” Often she doesn’t, but performing rapid, and often sloppy, experiments increases the odds of discovering something new.

Out of the Scientist’s Garden by Richard Stirzaker

Picture of the cover of "Out Of The Scientist's Garden- A Story Of Water And Food"

Lauren Crawford: “Richard Stirzaker is a scientist out of Australia committed to finding tools to make farming easier and more productive in third world countries.  I love how he talks about what happens when he uses water from his washing machine on his garden and the unanticipated effects: what does the detergent do to the fertilizers and the soil properties?  It’s a scientific view of how a garden works.”

Introduction to Water in California by David Carle

The cover of the book "Introduction To Water In California" by David Carle

Chris Lund: “This is a great introduction to California’s water resources, from where the water comes from to how it is used….particularly relevant today given California’s ongoing drought and the hard choices California faces as a result.”

The Drunkard’s Walk:  How Randomness Rules our Lives, by Leonard Mlodinow

A picture of the cover of the book "The Drunkard's Walk- How Randomness Rules Our Lives" by Leonard Mlodinow

Paolo Castiglione:  “The Drunkard’s Walk’s beginning quote perfectly reflects the author’s thesis: “In God we trust. All others bring data!”. I enjoyed the author’s discussion on how the past century was strongly influenced by ideologies, in contrast to the present one, where data seems to shape people’s actions and beliefs.”

Chapter 13 of An Introduction to Environmental Biophysics, by Gaylon Campbell

A picture of the cover of the book "An Introduction To Environmental Biophysics" by Gaylon S. Campbell and John M. Norman

Colin Campbell:  “Because of teaching Environmental Biophysics class, all my focus has been on reading An Introduction to Environmental Biophysics.  And, although I’ve read it too many times to count, I finally had a chance to study the human energy balance chapter (13) in depth, which was amazing.  The way humans interact with our environment is something we deal with at every moment of every day; often not giving it much thought. In this chapter, we are reminded of the people of Tierra del Fuego (Fuegians) who were able to survive in an environment where temperatures approached 0 C daily, wearing no more than a loincloth. Using the principles of environmental biophysics and the equations developed in the chapter, we concluded that the Fuegian metabolic rate had to continuously run near the maximum of a typical human today. The food requirements to maintain that metabolic rate would be somewhere between the equivalent of 17 and 30 hamburgers per day (their diet was high in seal fat).  You can read more about the Fuegians here.”

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

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A History of Thermocouple Psychrometry

Dr. Gaylon S. Campbell gives a short history on his involvement in the development of thermocouple psychometry:

seedling in a cup

A psychrometer measures wet and dry bulb temperatures of air in order to determine the relative humidity or vapor pressure.

The Original Psychrometers:

I started working with psychrometers in Sterling Taylor’s lab when I was a sophomore at Utah State University in 1960.  A psychrometer measures wet and dry bulb temperatures of air in order to determine the relative humidity or vapor pressure.  In a conventional psychrometer, a thermometer bulb is covered with a wet wick and measured to find the wet bulb temperature.  A thermocouple psychrometer is used to measure the wet bulb temperature of air equilibrated with soil or plant samples. When a plant is at permanent wilting point, its relative humidity is close to 99%, so the whole range of interest for soil and plant measurements is between 99 and 100% RH. The measurements need to be very precise.  To make a wet bulb we couldn’t use a wick. We made thermocouples from 0.001” chromel and constantan wires. We cooled the measuring junction of the wires by running a current through it (cooling using the Peltier effect), condensed dew on the wires through the cooling, and then read the wet bulb temperature by measuring the thermocouple output as the water evaporated.  We needed to measure temperature with a precision of about 0.001 C.

Diagram of isopiestic psychrometer used to measure the water potential of plant tissue.

Diagram of isopiestic psychrometer used to measure the water potential of plant tissue. Image:

A New Idea:

The original psychrometers we used in Dr. Taylor’s lab were single junctions mounted in rubber stoppers and placed in test tubes in a constant temperature bath. They were calibrated with salt solutions.  Typically, before we could finish a calibration, we would break the thermocouple, so we never got data on soils. I found that frustrating, so had the idea of putting the thermocouple in a sample changer which would hold 6 samples. The sample changer went in the constant temperature bath. When it was equilibrated, we could make 6 readings without taking it out or opening it up. Calibration was done in one try, and we could start running soil or plant samples right away. This was a huge improvement. Our lab was one of a very few who could even make those measurements, and we could make them six at a time. That was about 1964.

Two New Businesses Born:

Later, when I was a graduate student at WSU, I started building soil psychrometers for my own research.  Other researchers wanted them, so I taught Marv Sherman, a vet student friend to do the manufacturing, and we sold the psychrometers to whoever wanted them for the cost of his time plus materials.  There was a sizable and growing demand when he and I graduated, and no one to carry on.  My brother Eric came for my graduation.  We asked him if he would like to take over the psychrometer business, and he said yes.  We sent him home with some instructions and the materials we had left from Marv’s work.  Eric built the business himself and then sold it to Wescor, where he and my brother, Evan became employees.  I contributed ideas and helped Wescor grow for a few years, but Eric and Evan were not satisfied there and wanted to start a business of their own.  We came up with the idea of them building a laser anemometer, and that was the start of Campbell Scientific.

Image of Decagon's retired SC10/NT3 thermocouple psychrometer

Decagon’s retired SC10/NT3 thermocouple psychrometer

More Improvements:

When we were on sabbatical in England in 1977-78 I had access to a small machine shop and a machinist who was willing to make things for me.  The sample changer psychrometers up to this time all had to be used in carefully controlled constant temperature water baths.  However, the soil psychrometers that my brother, Eric, sold at Wescor worked fine with no temperature control.  I suspected it would be possible to make a sample changer that didn’t need a constant temperature bath.  I made some sketches and the machinist made it for me.  It had places for 10 samples, had a large aluminum block to hold the rotor with the samples and the thermocouple, and stood on 3 legs.  It worked fine without any temperature control.

I showed the new sample changer to my brothers at Campbell Scientific, and they set up and machined a couple of them.  CSI didn’t have much interest in selling psychrometers, though, so Decagon began as a way for my children to earn money for college by selling the thermocouple psychrometer sample changer.  The name Decagon came both from the 10 people in our family when we started and the 10 samples in the sample changer.

Thermocouple Psychrometry Fades into History:

Decagon (now METER) began selling the thermocouple psychrometer system in 1982 and updated the user-intensive calibration and measurement system to a much simpler one in the mid-1990s.  Automation, speed, simplicity, and accuracy soon tipped the scales in favor of a dewpoint technique for measuring water potential, and the system was retired and replaced by a chilled mirror hygrometer (WP4C) in 2000.  However, Dr. Campbell believes that thermocouple psychrometers may still have a role to play in measuring water potential. If you’re interested in water potential, check out our water potential pages. It puts many of our best water potential resources in one place and contains sections on theory, measurement methods, and history.

Download the “Researcher’s complete guide to water potential”—>

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

Get more information on applied environmental research in our

Founders of Environmental Biophysics Series: Sterling Taylor

Gaylon Campbell’s first experience with environmental measurement came in the lab of Dr. Sterling Taylor at Utah State University, where he was asked to make water potential measurements in order to understand plant water status. What he learned with Dr. Taylor became the start of four scientific companies and gave Dr. Campbell the tools and the confidence to become one of the world’s foremost authorities on physical measurements in the soil-plant-atmosphere continuum.  Here’s what Dr. Campbell had to say about his association with Dr. Taylor:

Sterling Taylor 1918-1967 Image: dlscience

Sterling Taylor 1918-1967 Image: dlscience

Who was Sterling Taylor and why is he considered one of the Founders of Environmental Biophysics?

Sterling Taylor was professor of Soil Physics at Utah State University.  He did his undergraduate work at what was Utah State Agricultural College, and earned his PhD at Cornell University. He worked on both theoretical and practical problems in soil physics.  His practical work focused on research in the area of plant-water relations and irrigation management.   Dr. Taylor worked out water potential limits for both maximum and reduced growth rates of crops. The irrigation limits tables that he put together are still used in today’s handbooks.  His theoretical contributions were on linked transport and applications of non-equilibrium thermodynamics to soil physics, which he was working on at the time of his death.   Dr. W. H. Gardner, a soil physicist of the time, called the amount of work Dr. Taylor and his students did “unparalleled” and noted that attendees at regional conferences often had to carry Taylor’s “weighty reports” home as overweight baggage.

Corner of a bound note book

Attendees at regional conferences often had to carry Taylor’s “weighty reports” home as overweight baggage.

What was your association with him, and how did he influence your life and your science?

Sterling was a kind of second father to me and to many other young scientists.   He loved to help boys and teach them what their potential was.  At that age, I didn’t have any idea that I could do anything in science. The first assignment he gave me was to set up an experiment to measure the simultaneous movement of salt and water in soil.  I had no idea what I was doing, and it was a challenging project.  It would be challenging for me to do it right now!  But he’d give me ideas about how to do the next thing, I’d try to do it, and eventually I got some data that he thought was useful.  He did some analysis of it, and that’s how I learned to measure electrical conductivity and salt concentration in water and soil.  Sterling’s lab is also where my brother Eric and I learned how to make thermocouple psychrometers and other instruments for environmental measurements.  Those insights led directly to the start of Wescor and Decagon.  Campbell Scientific, Juniper systems and others eventually came from those beginnings.

Dr. Taylor was also a very patient man. He made a precision constant temperature bath out of an old washing machine.  It had an agitator in the middle to stir the water while cooling it with coils around the outside of the tub.  It was a wonderful setup, and he took a lot of pride in how well it worked.  He came into the lab one day while I was making some modifications to it.  I was drilling a hole through the outer jacket around the Freon(™) coils where the refrigerant ran.  He said, “Now be careful if you’re drilling holes through that thing so you don’t hit the coils”.  And I said, “Yes, I’m being careful.”  But I wasn’t.  The coils were a couple of inches apart, and I thought, There’s no way I’m going to hit one.  I didn’t even get a ruler.  I just eyeballed it, drilled a hole, and hit the tube dead on.  I couldn’t have hit it more perfectly if I’d measured as carefully as I could. All the refrigerant came hissing out, and I thought he would hear it over in his office.   He probably did hear it, but he didn’t come out to see what was going on.  One of the hardest things I ever did in my life was to go in and tell him I’d drilled a hole in his refrigerant tube.  He just said, “Well…I guess we’ll have to get some new refrigerant.”  He was just patient, and knew how to work with young people.

Student Examining a Textbook Reading the Pages at a Desk in a Classroom

I made a career choice to be a teacher and have students.

But that wasn’t the only way he influenced me.  As it came time for graduation he gave me some advice that had an enormous impact.  Once when I was trying to choose between soil physics and medical biophysics he said “do you want to be a little duck in a big puddle or a big duck in a little puddle?”  I decided on the little puddle.  On another occasion, I was wondering what kind of soil physics position would be best.  One of his former students had gotten a job at an experiment station near Kimberly, Idaho, and I thought that would be ideal.  He observed, “Those can be fun jobs, but if you go to a position like that you just don’t have any offspring.”  That resonated with me, and I thought, “I would like to have offspring.”  So I made a career choice to be a teacher and have students.  It was wonderful to have had that kind of advice at that critical time.

What do you think we missed because he died so early?

It’s interesting to think about scientific contributions and other types of contributions people make.  One of my sons gave me a book of science cartoons, and one of those cartoons shows a couple of scientists talking together. One of the scientists says to the other, “Isn’t it sad to think that everything we come up with now will be disproved in 20 years?”

It just shows you what a transient thing our work is. We think it’s so important, but the important contributions that Sterling made were the numbers of people that he influenced so profoundly.  I’m not the only one he was a second father to.  Sterling Taylor had a huge family of students.  Many went on to prestigious institutions like CalTech (California Institute of Technology), making important contributions over their careers.  And they trace it back to Sterling’s influence on them.

How can scientists today emulate the great man that he was?

I think it would be to not take science so seriously but to take interactions with their fellow travelers seriously. There is a quote by Clayton Christensen from an article in Harvard Business Review on how to emulate what Sterling Taylor was. Christensen says, “I’ve concluded that the metric by which God will assess my life isn’t dollars but the individual people whose lives I’ve touched.  I think that’s the way it will work for us all. Don’t worry about the level of individual prominence you have achieved; worry about the individuals you have helped become better people. This is my final recommendation: Think about the metric by which your life will be judged, and make a resolution to live every day so that in the end, your life will be judged a success.”

Download the “Researcher’s complete guide to water potential”—>

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

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4 Funding Tips from an Experienced Grant Writer

Dr. Richard Gill developed an interest in ecology as a child while exploring the forests and seashores of Washington State. This attraction to wild places motivated Dr. Gill to study Conservation Biology as an undergraduate at Brigham Young University and to receive a PhD in Ecology from Colorado State University.

Dr. Richard Gill

Dr. Richard Gill, ecologist at BYU

His PhD research on plant-soil interactions in dryland ecosystems, supervised by Indy Burke, dovetailed well with his postdoctoral research on plant physiological ecology with Rob Jackson at Duke University. Dr. Gill returned home to Washington in his first faculty position at Washington State University. There he pursued research on global change ecology, studying the impacts of changes in atmospheric CO2, temperature, and drought. In 2008 he joined the faculty of Brigham Young University as an associate professor of biology. He teaches Conservation Biology courses and in the general and honors education curriculum.

Dr. Gill has been successful in obtaining funding from the National Science Foundation, the U.S. Department of Agriculture, U.S. Dept of Energy, and the U.S. Department of the Interior.  He also helped guide one of his graduate students in winning research instrumentation from the Grant Harris Fellowship, provided by METER.  We interviewed him about his thoughts on successful grant writing.  Here’s what he had to say:

  1. Understand the call: I think it’s important to understand what’s being asked of you and write to the call for proposals itself.  We all have ideas, and we think everybody should give us money for every idea that we have.  That’s part of being a scientist, but understanding the parameters and the purpose of the grant is crucial.  This is because the easiest way to eliminate proposals is to cull those that don’t address the call.  In this way, proposal readers go from a stack of 200 to a stack of 50, without having to get into the details of the research at all.  So my advice is to read the call for proposals, and make sure you actually address what they ask for and stick to the requirements for length and format.
  2. Be true to the vision: There is always some sort of vision tied to the call, so make sure you are true to that vision.  For example, let’s say it’s the Grant Harris Fellowship, which provides instrumentation for early career students to do something they wouldn’t otherwise be able to do.  Make sure you say, “Here’s what I’m already doing with the funding and instrumentation that we have in our lab.  There’s a key component missing, and I can only do it if you support me.”  Show a clear need, aligning your research with the purpose of the proposal, and you’ll have a strong case for funding.
  3. Make sure you edit: Many proposals don’t get funded because of poor writing.  Your great ideas can’t come forward if the reader is mired down in your verbiage.  Don’t send them your first draft.  Make sure you have somebody read it for clarity.
  4. Be clear and concise: When scientists are involved in a project, it is common to develop a sort of tunnel vision, a byproduct of having worked on the project for years and being familiar with all the details.  When you write a proposal you should remember that the person who is reading is going to be intelligent, but have no idea what you’ve been doing.  You should say, “Here’s what I’m going to study, why I’m going to study it, and how I’m going to test it.”  Be clear, specific, and declarative.

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

Get more information on applied environmental research in our

Founders of Environmental Biophysics Series: John Monteith

We interviewed Gaylon Campbell, Ph.D. about his association with one of the fathers of environmental biophysics, John Monteith.

John Lennox Monteith

John Lennox Monteith,

Who was John Monteith?  

John Monteith was a professor at the University of Nottingham in England and one of the founders of modern environmental biophysics.  He pioneered the application of physical principles in the study of how plants and animals interact with their immediate environment.  He started his career at Rothamsted Experimental Station in Harpenden, England and was hired as professor at Nottingham in the early 1970’s.  He went on to spend time at the International Crops Research Institute for Semi-Arid Tropics (ICRISAT) in India.  He published a textbook that has been a foundation for Environmental Biophysics, called Principles of Environmental Physics.   He was elected a member of the Royal Society of London, which is the highest scientific distinction a person can receive in the UK.   He was also a member of the Royal Meteorological Society and was its president in 1978.  These societies are both sponsored by the crown, and he told me on the occasion that he was installed as the president of the Royal Meteorological Society, the queen attended and he sat by her at dinner.  He is known for the Penman-Monteith equation that has become the basis for guidelines for estimating irrigation water requirements used by the FAO (Food and Agriculture Organization of the United Nations).

How did you meet him?

As an undergraduate, I knew of John because I worked for a professor at Utah State University (Sterling Taylor), who was measuring water potential in soil using thermocouple psychrometers. I was keenly interested in the subject, so Dr. Taylor gave me a paper on thermocouple psychrometers to read, published in 1958 by Monteith and Owen, written while John was at Rothamsted.   John’s work there was influential in developing instrumentation which formed the foundation for Wescor, METER, and several other companies.

When Prof. Monteith’s book came out, it was pretty exciting for me, because it had everything in it that I was trying to teach as a professor of Soil Science.  I wrote to John in 1977 inquiring about the possibility of doing a sabbatical there, and he wrote back immediately and arranged for us to come.  Amazingly, he and his technician met our big family at Heathrow airport and loaded up the whole crew, including our many duffel bags, into a university minibus.  A couple of our bags were missing, and John picked them up from the railway station in Nottingham and delivered them to us the next day.  I have often marveled that such a busy and important man would take the time to care for us like that.

Yellow Sunflower

A sunflower field in Karnataka, India

What was he like as a colleague?

He was a humble man in a lot of ways.  After he passed away, one of his colleagues wrote in and told about some of the experiences he’d had with John in India.  India has a pretty hierarchical society, and it’s not uncommon for somebody who is in a position of authority to take advantage of that.  John was in charge of one of the big groups within ICRISAT, and the thing that impressed his colleague was that whoever came into John’s office was treated with great respect, whether it was the cleaning person or the lab technician.  If they had come to see him, they got the same treatment and the same respect that the director of the lab got.

We worked on a lot of projects together, but the proposal we submitted that was funded was one on improving thermocouple psychometry.  I wrote up the paper, but he had written the proposal and provided the funding for the work.  I put him down as an author on the paper, and when I got ready to submit it, he went over the paper just as if he were an author and then crossed his name out.  He said he hadn’t contributed enough.  Well, he contributed way more than most authors do, but he had a set of standards that he expected himself to meet and his contributions to that paper hadn’t met those standards. He was pretty amazing that way.

How did he get to be a part of the Penman-Monteith Equation?

Penman was head of the research group at Rothamsted Experimental Station which Monteith joined, following graduation. Penman was already an established researcher by the time Monteith got there, and the Penman equation was already well known. But, Monteith worked with that equation, and in my opinion, improved it substantially. He never wanted to take credit for that. He always claimed that Penman already understood the things he had added, and he never did call it a Penman-Monteith equation, always referring to it as the Penman equation. But I have never read things of Penman’s that indicated that he had anywhere near the depth of understanding of the equation that Monteith had. To my way of thinking, it’s completely appropriate that his name is associated with it.

What was John’s secret to accomplishing all he did, and how can scientists today emulate his meaningful career?  

His gift was the gift of clear thinking. I gave a talk about him a while ago entitled “Try a Straight Line First.” John hated the complexity of modern computer models for crop growth because he couldn’t easily see the end from the beginning in those models.  He had the ability to look at a problem, no matter how complex, and just reach in and grab the essence of that problem and show it to you.  He used to talk about Occam’s Razor and not multiplying complexity. Einstein was supposed to have said, “Everything should be as simple as possible, but not simpler.”  John was always able to find a simple way to look at problems.  It may have been a complex process to get there, but once he was done, you had something that you could manipulate.  I think simplicity and uncluttered thinking would be the thing to emulate.

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The Spirit of the Grant Harris Fellowship

The Grant Harris Fellowship was conceived in 2009 by  METER‘s (formerly Decagon Devices) marketing group as an opportunity for METER to give back to the science community.  The idea was to create a partnership between METER and researchers so that we could provide instrumentation and be a kind of “scientific friend” to graduate students: giving them experience crafting a proposal, reviewing their ideas, offering feedback, and encouraging those projects that seemed the most promising and exciting to us as scientists.

Grant Harris fellowship

Grant Harris standing in the doorway of METER’s first office in 1987.

When we thought about this opportunity we wondered…who would we name this fellowship after? It was an easy decision when we realized that the principles upon which METER is based come from academia through our founder, retired soil science professor Gaylon Campbell and his father-in-law, Grant Harris, who was a professor and department head of Rangeland Ecology at Washington State University.

Grant Harris fellowship

He lived in a tiny outpost of a house, taking care of sheep-grazing rangeland in a high alpine meadow area, far removed from civilization.

Grant Harris started his career at the beginning of the depression, so when he got married he quickly needed to find a way to support his growing family.  At that time in history, there was not as much college funding or support.  Instead of having the opportunity to attend graduate school, Dr. Harris was forced to start work immediately after obtaining his B.S. for the U.S. Forest Service, managing rangeland in Montana. He lived in a tiny outpost of a house, taking care of sheep-grazing rangeland in a high alpine meadow area, far removed from civilization.

“Scientific Instrumentation has made a lot of progress since I was first exposed to research, working at the Desert Range Experiment Station in 1935 as an undergraduate at Utah State University.  Back then research was 3 parts wits, 6 parts labor, and 1 part instrumentation. I still remember in 1939 measuring the absorption of water into the soil profile using old whisky bottles and corks.

It is amazing to see the time and labor saving devices now available.  We are proud of Decagon’s heritage in producing instrumentation for soil physics.” – Grant Harris

It was only later, after five years of service in the U.S. Navy during WWII, that he finally got the chance to further his education. He returned to school to earn an M.S. and a PhD, and because of his difficult path in obtaining those degrees, he placed a high value on education and an even greater value on the providing of opportunities for research.

Grant Harris fellowship

He placed a high value on education and an even greater value on the providing of opportunities for research.

During his career, Dr. Harris was able to reach out and touch the lives of many students, not only in the U.S. but from all over the world.  He spent time in other countries researching and helping to provide basic science to people throughout his career as a rangeland ecologist.  The Grant Harris Fellowship provides that same learning opportunity for graduate students today where, in the spirit of this legacy that Grant Harris provided, we continue his passion for encouraging research in a direction that will help us understand more about the natural environment.

Colin Campbell, Decagon’s VP of Research and Development commented on the “Spirit of Grant Harris,” during a recent interview.  “As we thought about this opportunity to give back to the research community, we thought of my grandpa, who had a great passion for providing people the chance to learn and grow through the beauty of science.  Thus the objective of the Harris Fellowship is to provide student researchers additional opportunities to dream up new ways of doing things that are going to be successful and also to provide support to those researchers so they can accomplish their goals.”

Click here to learn more about how to apply for the annual Grant Harris Fellowship

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Do Funding Agencies Favor Collaboration?

It’s an interesting question, and certainly one scientists need to think about. In a recent conversation a science colleague said, “I think in science right now, all the funding agencies are recognizing that to answer the problems that matter, you need to bring in people from different disciplines and even industry. If you look at the major funding focus of the National Science Foundation, when they consider bio-complexity, they’re not looking for a group of people with the same perspective. Science questions are becoming more complex, so you need to get input from people with varied backgrounds.”


R.J. Cook Agronomy Farm at WSU (

Examples of this are two projects that METER has collaborated on recently: the Specialty Crops Research Initiative – Managing Irrigation and Nutrients via Distributed Sensing (SCRI- MINDS) and the WSU Cook Farm project, both of which were able to get funding based in part on the use of METER’s technology, and both had a high-level of multidisciplinary involvement.

We got involved in the Cook Farm Project seven years ago because another scientist and I had an idea that fit in the context of a hot topic of the time which was to create a wireless sensor network that was densely populated in a relatively small area.  We did this because at that time, scientists were recognizing that many of the processes they were interested in were occurring when they were not out in the field measuring. In order to understand these processes, we needed in situ measurements collected continuously over a long period of time.

What we were trying to do is show that you could create a wireless sensor network in a star pattern, where you have a central point collecting data from a host of nodes surrounding it.  Our questions were:  can we create a sustainable star network in the field to get consistent and continuous measurements over several seasons, while densely populating the study area with sensors? The measurement network that we designed allowed us to investigate how topography, slope, and aspect interact to determine the hydrology of the soil in this intensely managed agronomic field.

Decagon collaborated with scientists at Washington State University, working with twelve sites across a 37-hectare field.  We installed five ECH2O-TE (now 5TE) sensors at 30, 60, 90, 120, and 150 cm below the soil surface.


Wheat field

What we learned was that when wheat plants grow, their roots follow the water down a lot deeper than you might imagine.  We observed considerable water loss even 150 cm below the soil surface. Data on soil water potential suggested that, as water was depleted to the point where it was not easily extractable, plant roots at a given level would move deeper into the soil where water was more easily accessible. Soil morphology also came into play as hardpans occurred at several measurement locations and water uptake from layers above and below them showed amazing differences.

It was a really exciting thing scientifically, but also technologically.  We learned that the star network was easily possible.  It ran autonomously and was very successful, in spite of the fact that the cell phone we used to get the data back to the office never worked very well.

So it was the science question and the technology question together that was able to secure the funding.  With those twelve sites WSU was able to secure a grant from the USDA for 4.2 million dollars and the research is still ongoing today.  In fact, recently Cook Farm was established as one of the National long-term agroecosystem research sites (LTAR) which will help continue this kind of research well into the future.

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Dr. Gaylon S. Campbell Author Interview

METER’s founder, Dr. Gaylon S. Campbell was born in Blackfoot, Idaho, and grew up on a dry farm in Juniper, Idaho.  He went to school in Logan, Utah, finally attending Utah State University where he received a B. S. in Physics in 1965 and an M. S. in Soil Physics in 1966.  He was granted a Ph. D. in Soil Physics from Washington State University in 1968.  He became an officer in the U. S. Army in 1969, doing meteorological research at White Sands Missile Range, New Mexico.  In 1971 he returned to Washington State University as Assistant Professor of Biophysics and Assistant Soil Scientist.  There he taught and did research in Environmental Biophysics and Soil Physics until 1998.  Since 1998 he has worked as vice president, engineer, and scientist at Decagon Devices, Inc (now METER).  He has written three books, over 100 refereed journal articles and book chapters, and has several patents.  Today we are interviewing him about his book, An Introduction to Environmental Biophysics.

Gaylon S. Campbell

Dr. Campbell is the author of An Introduction to Environmental Biophysics

Where did you get the knowledge to write the book?

I was hired to teach Environmental Biophysics at Washington State University in 1971, and when I looked around for a textbook to go with the class, there weren’t any that fit very well.  I knew what I wanted to teach in the class, and some of the principles were in books that were available, but a lot weren’t.  So I started writing up notes to hand out to the students and then improved them over time.

One of the important sources of knowledge for my book was John Montieth’s book, Principles of Environmental Physics.  Its first edition came out in 1973. It’s a wonderful book.  I didn’t know about it until one of my students brought it into class and let me borrow it overnight.

I went home and started reading it.  I read it all night, and by morning I’d finished it.  I have read some novels that could keep me awake all night, but that’s the only science book I ever read that could do it.

I was really excited about his approach because it was perfect for what I wanted to do in the class. However, it was at a different level than I needed, so I went ahead and developed my own notes, but his book certainly was an important source.

Gaylon S. Campbell

I started writing up notes to hand out to the students and then improved them over time.

How difficult was it to understand the theory behind what you were writing about?

When I’d take a class in school, I felt like I never understood what was in that class until I attended the next class.  Then when I got a bachelor’s degree, I thought, I hope nobody expects me to know something just because I have this degree, because I don’t feel like I know anything.  I hoped when I earned a masters degree that it would be better, but I got there and thought, oh boy, I still don’t know anything.  It was probably when I took my prelim exam that I finally felt confident enough that I could be a soil physicist if I had to.

But I was wrong about that.  I really didn’t understand physics very well, even then.  It was when I had to teach it that the real understanding came.  When I understood it well enough to lecture about it was when I felt like I had really mastered the theories and understood them at the level that I wanted to.

I suppose that came one piece at a time.  In the beginning, I certainly didn’t understand things as well as I did later on.  And that still happens today.  I learn things that I hadn’t understood before.  So I guess when you ask how hard it was:  it was an ongoing process. Even when somebody’s already laid it out for you, it doesn’t mean you’re going to understand it.  But when you lecture about it and write about it, those are the processes that help to deepen your knowledge and understanding.

Gaylon S. Campbell

When you lecture about a subject and write about it, those are the processes that help to deepen your knowledge and understanding.

The subject is extremely complicated, but people are always saying how easy it is to understand environmental biophysics from your book.  How did you bring it down to the level of the students?

When I was in the Army, the philosophy they had was, “If the student hasn’t learned, the teacher hasn’t taught.”  That was not the philosophy that you normally encountered at the university.  Many professors complained often about how lousy their students were.  I never found it to be that way.  I always thought my students were getting better and better.

I think it comes down, to some extent, to the philosophy the teacher has.  We often see teachers come in and fill the board with equations and wonder why their students don’t understand them.  But it’s likely the teacher hasn’t looked at it from the standpoint of the students.  The student is going to gain understanding by the same path the teacher did.   Professors work and work to put together a wonderful picture of things, and once they have that wonderful picture, they tend to want to dump the whole thing on the student.  But students can’t assimilate the whole picture all at once.  They have to go step by step too.

If people wanted to learn from your book, what is the best way to get the principles down?

It’s no accident that there are lots of both worked examples and problems for students to solve.  I don’t think you can learn physics without solving problems, and so the best way to do it is to look through the ones that we’ve solved in the book and then look through the problems we give at the end of the chapters and solve them.  That, I think, is the best way to get there.

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