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Posts by Colin Campbell

Mar 7

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Data loggers: To Bury, or Not To Bury

Globally, the number one reason for data loggers to fail is flooding. Yet, scientists continue to try to find ways to bury their data loggers to avoid constantly removing them for cultivation, spraying, and harvest.  Chris Chambers, head of Sales and Support at METER always advises against it.  He warns,  “Almost all natural systems, even arid ones, will saturate at least once or twice a year—and it only takes once.”  Still…there are innovative scientists who have had some success.

A prototype buriable logger container made from a paint can with sensors attached

A prototype buriable logger container, made from a paint can, PVC elbow, silicone, epoxy putty, and desiccant. Photo Credit: NDSU | Soil Sciences | Soil Physics

The Good

Radu Carcoana, research specialist and Dr. Aaron Daigh, assistant professor at North Dakota State University, use paint cans to completely seal their data loggers before burying. They drill ports for the sensor cables, seal them up, and when they need to collect data, they dig up the cans.  Chambers comments, “So far it looks promising, but we had a long discussion about the consequences of getting any water in those cans. I don’t know what they were sealing the ports with, but they were pretty confident that they could even dunk their paint cans under water.”  The North Dakota research team buried the paint cans last fall, and Chambers says he’s reserving judgment until spring.  Radu comments, “The picture above is just the concept.  The story will continue in April when we see the North Dakota winter toll.” (See update).

The Bad

Chambers has good reason for his skepticism.  If a logger gets saturated even once, its life will be short.  And even if it doesn’t get completely flooded, there is still risk.  As water gets into the enclosure that encases the logger, the resulting high humidity can damage the instrument.  Chambers says, “If loggers that are mounted on a post get a small amount condensation or water inside, they’ll be fine.  But the buried ones have no escape route for water vapor.  If they get wet or are exposed to water vapor even once, they are going to fail. We’ve seen horror stories time and time again. It’s just not a good environment for electronics.”

Five gallon white bucket with rocks and dirt in it

One group of scientists tried burying their loggers in five-gallon buckets.

The Ugly

Chambers likes to relate a cautionary tale about some scientists in Seattle, who buried their data loggers in five-gallon buckets with lids.  They taped their loggers to the lid, but when they dug the buckets up, they were half full of water, and the loggers were dead.  This is because as the buckets filled with water, the loggers were continuously exposed to water-condensing conditions.  After the loggers were repaired, the scientists re-buried them. But, six weeks later, their buckets were again half full of water, and their loggers were dead.

One Success Story So Far

There is one innovative group at Washington State University, however, who can be considered successful.  Postdoctoral research associate Caley Gasch decided she wanted to bury data loggers in the Cook Agricultural Farm, an actively managed field, so they weren’t constantly taking down loggers and causing large gaps in their data.  

Next week: Find out how she was able to solve many of the problems that prevent successful deployment of data loggers underground.

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Feb 25

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Irrigation and Climate Impacts to the Water-Energy Balance of the WI Central Sands (Part II)

Due to controversy over the growing number of high capacity wells in the Wisconsin Central Sands, University of Wisconsin PhD student, Mallika Nocco, is researching how agricultural land use, irrigation, and climate change impact the region’s water-energy balance (see part I).  This week, read about her challenges installing lysimeters below the root zone, how she used a GPS system that can find the lysimeters within a half-inch of accuracy, and her surprising conclusions.

Irrigation sprinkler line set up in a grassy field

This relatively small ecological region has gone from 60 high capacity wells in 1960 to over 2,500 today.

Below the Root Zone

Nocco says getting the lysimeters below the root zone was a major challenge.  “We tried a couple of things, but we settled on installing all the lysimeters with an 18-inch auger that would drill a hole slightly bigger than the whole lysimeter.  We dug an 80 cm trench to the top of the monolith zone. Then, we pounded the drain gauge divergence control tube to 1.4 m to obtain an intact monolith, wherever it was possible to do so. We also stratified soil moisture sensors at 10, 20, 40, and 80 cm.  We used heavy equipment to slowly lift out the monolith, dig out the soil below, and place it back in, keeping  track of all of the different soil horizons, and backfilled as close to the bulk density as we could.”

Researcher filling a hole with dirt and a tube with dirt

Passive capillary lysimeter installation

Finding the Lysimeters with GPS

Typically, scientists bury lysimeters close to the edge of the field so they are easy to locate, but Nocco was concerned that they would prejudice their data due to the donut effect of center pivot irrigation: more irrigation hits the center of the field with less irrigation toward the edges. She comments, ”When I installed the first ten lysimeters, I had not yet come up with a way to find everything. Those instruments are all about 15 meters from the field edge so that I could triangulate measurements and find them during cultivation.  But then I met an extension scientist at the university who had access to an RTK GPS system, which can locate instrumentation within a half-inch of accuracy.  With his help and training, we were able to install the rest of the lysimeters at more random spots throughout the field.”

Irrigation sprinkler line set up in a pastor or field

Nocco was concerned that they would prejudice their data due to the donut effect of center pivot irrigation.

Surprising Conclusions

Nocco says that ET and differences in crop physiology do not explain or account for all of the variability that she saw in groundwater recharge.  Her team did a particle size analysis on the soils adjacent to the lysimeters, and she comments, “We thought that the greater the relative sand content in the soils, the more recharge we would have seen, but what we are seeing is the opposite.  The particle size analysis reveals a negative linear correlation between potential recharge and sand content. The more silt there is in these lysimeters, the more volume of recharge.  What I’m curious about now is if we’re seeing a greater volume of recharge in the siltier spots from flux convergence.  I’m trying to obtain the time series data from the pressure transducers to see if maybe the sandier areas had less potential recharge, but perhaps drained faster.  I have seen a correlation between antecedent soil moisture content and particle size (with no correlation based on crop type).  So it also looks like the siltier soils are holding more water when the rain comes through.”

What’s Next?

Eventually, Nocco plans to use field-generated estimates of groundwater recharge and ET to parameterize and validate a dynamic, agroecosystem model, Agro-IBIS, simulating hydrological responses to climate and land use changes over the past 60 years. Nocco will then share the water-energy budgets and water quantity/climate simulations with stakeholders in the Wisconsin Central Sands area.

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Feb 17

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Irrigation and Climate Impacts to the Water-Energy Balance of the WI Central Sands (Part I)

Due to controversy over the growing number of high capacity wells in the Wisconsin Central Sands, University of Wisconsin PhD student, Mallika Nocco, is researching how agricultural land use, irrigation, and climate change impact the region’s water-energy balance.  She and her team have uncovered some surprising results.

Fisher women leans in for a kiss with a class 1 trout she caught

A class 1 trout stream has sufficient natural reproduction to sustain populations of wild trout at or near carry capacity.

Water Use Debate

There are class 1 trout streams in the Central Sands region, and some people worry that the increasing number of high capacity wells used for agriculture will reduce the water levels in those streams.  “Lake Huron has lost about 11 feet of water since 2000,” says one resident of the Central Sands area, “and water levels are continuing to drop.” In 2008, the small well he used to pump drinking water went dry, and he blames the high capacity wells.” (Aljazeera America)  On the other side of the debate, agriculture irrigated by these wells is extremely valuable to the state, and growers have taken quite a bit of time to understand the water cycle and their role in it. You can read about their water management goals and accomplishments here.

Updating Former Research

Irrigated agriculture wasn’t prevalent or profitable in the Wisconsin Central Sands until groundwater irrigation with high capacity wells became feasible in the 1950s.  Since then, this relatively small ecological region has gone from 60 high capacity wells in 1960 to over 2,500 today.

Mallika Nocco is studying potential groundwater recharge from irrigated cropping systems that use the wells, hoping to understand if the irrigation water is lost or returned to the groundwater.  She says, “Until now, we’ve been relying on models validated by two lysimeters in the 1970s. Champ Tanner (one of the fathers of environmental biophysics) designed the weighing lysimeters, and they were very accurate, but we wanted to do a larger scale study with multiple crops to get a handle on interannual variability and to improve our understanding of recharge in the region so we can do a better job of managing irrigation and groundwater.”

Lysimeter installation into a dirt and a field

Lysimeter installation into actively managed fields presented challenges that the research team had to overcome.

Measuring Recharge

Nocco used twenty-five drain gauge lysimeters to capture vadose zone flux under potato and maize cropping systems.  She monitored soil water (and temperature) flux by stratifying water content sensors from the soil surface to a depth of 1.4 meters.  She also estimated evapotranspiration (ET) using a porometer to measure stomatal conductance, in addition to obtaining micrometeorology, leaf area index, and gas exchange measurements.

Nocco and her team had to put their sensors in to avoid cultivation, so they extended the drain gauge PVC that comes up to the soil surface and removed it any time there was major fieldwork, whether it was tillage or planting, so that the area over the lysimeter got the same treatment as the rest of the agricultural fields.

Below the Root Zone

Nocco says getting the lysimeters below the root zone was a challenge.  Next week, read about how she solved that challenge, how she used a GPS system to find the lysimeters within a half-inch of accuracy, and about her surprising conclusions.

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Feb 4

Predicting the Stability of Rangeland Productivity to Climate Change

Dr. Lauren Hallett, researcher at  the University of California, Berkeley, recently conducted a study testing the importance of compensatory dynamics on forage stability in an experimental field setting where she manipulated rainfall availability and species interactions. She wanted to understand how climate variability affected patterns of species tradeoff in grasslands over time and how those tradeoffs affected the stability of things like forage production across changing rainfall conditions.

field with species tradeoffs standing in the brush

Species tradeoffs could help mitigate the negative effects of climate variability on overall forage production.

Species Tradeoff

A key mechanism that can lead to stability in forage production is compensatory dynamics, in which the responses of different species  to climate fluctuations result in tradeoffs between functional groups over time. These tradeoffs could help mitigate the negative effects of climate variability on overall forage production.  Dr. Hallett comments, “In California grasslands, there’s a pattern that is part of rangeland dogma, that in dry years you have more forbs, and in wet years you have more grasses. I wondered if you could manage the system so that both forbs and grasses are present in the seed bank, able to respond to climate.  This would perhaps buffer community properties, like soil cover for erosion control and forage production in terms of biomass, from the effects of climate variability.”

Tradeoff in a green field, aerial view

In areas experiencing moderate grazing, there was a strong species tradeoff between grasses and forbs.

Manipulating Species Composition

Dr. Hallett capitalized on the pre-existing grazing manipulation that her lab had done over the previous four years.  The grazing she replicated for this study was experimentally controlled, making it easier to ensure consistency.  She built rainout shelters where she collected the water and applied it to dry versus wet plots.  She also manipulated species composition, allowing only grasses, only forbs, or a mix of the two.  These treatments allowed her to study changes in cover and biomass.

Hallett used soil moisture probes and data loggers to characterize the treatment effects of this experiment and to parameterize models that predict rangeland response to climate change.  She says, “I wanted to verify that my rainfall treatments were getting a really strong soil moisture dynamic, and I found the shelters and the irrigation worked really well.”  Along with above-ground vegetation, she collected soil cores and looked at nutrient differences in conjunction with soil moisture.  Since her field site is located within the Sierra Foothills Research and Extension Center, Dr. Hallett was able to rely on precipitation data that was already measured on-site.  

Results

Dr. Hallett found that in areas experiencing moderate grazing, there was a strong species tradeoff between grasses and forbs.  She comments, “I had a seedbank that had both functional groups represented, and those tradeoffs did a lot to stabilize cover over time.”

When Dr. Hallett replicated the experiment in an area that had a history of low grazing, she found that the proportion of forbs wasn’t as high in the seedbank.  As a consequence, there was a major loss of cover in the dry plots.  She explains, “When the grass died, there weren’t many forbs to replace it, and you ended up with a lot of bare ground. The areas that were lightly grazed had more litter, so initially, the soil moisture was okay, but as the season progressed into a dry condition and the litter decomposed, there wasn’t enough new vegetation to stabilize the soil.”  As a result, Dr. Hallett thinks in low-grazed areas it’s important to have an intermediate level of litter. She says, “You need enough litter to increase soil moisture, but not so much that it would suppress germination of the forbs because as the season progresses and gets really dry, if you don’t have forbs in the system, you lose a lot of ground cover.”

Surprises Lead to A New Study

Dr. Hallett was surprised that within her three treatments there seemed to be differences in when the functional groups were drying down the soil.  This inspired new questions, leading her to use her dissertation data to generate a larger grant through the USDA.  Her new study will perform extensive rainfall manipulations to measure the effects of early-season versus late-season dryout, and vary species within those parameters.  She says, “One of the reasons you have grass years versus forb years is the timing of rainfall.  For instance, if you have a really dry fall, you tend to have more forbs because their seedlings are more drought resistant.  Conversely, if you have a wet fall, you tend to see more grasses because you have continual germination throughout the season. So, the timing of rainfall matters in terms of what species are in the system.  We are going to look at the coupling between the species that gets selected for the fall versus what would be able to grow well in the spring, and we will be studying how that affects a whole range of things such as ground cover, above-ground production for forage, below-ground investment of different functional groups, and how these things might relate to nutrient cycling and carbon storage.”

You can read more about Dr. Hallett’s rangeland research and her current projects here.  

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Jan 14

Using Soil Moisture Sensors on Humans?

Dr. Stuart Campbell, professor of Biomedical Engineering at Yale University has been toying with the idea of using soil moisture sensors to measure tissue edema in human subjects.

Patients had wrapped in gauze with a tube

Tissue edema occurs when too much fluid leaks from your capillaries into your tissue.

He says he got the idea from Dr. Ken Campbell, former professor of Bioengineering at Washington State University:  “I was explaining to Dr. Campbell about the sensors METER makes, and he pointed out that there are many diseases where you might want to measure someone’s tissue edema, and it would be interesting to see if you could use a soil sensor in a wearable device to help doctors monitor swelling in their patients, much like a heart monitor monitors heart activity.”

Tissue Edema:

Tissue edema occurs when too much fluid leaks from your capillaries into your tissue. Capillaries, the smallest blood vessels in your body, are somewhat leaky, allowing the exchange of nutrients and waste between the tissue and the blood. The fluid that surrounds the blood cells is free to exchange across the capillaries, and edema will occur when too much fluid leaks out of the circulatory system into the tissue.  Edema can be caused by things like heart disease, pregnancy, or standing on your feet all day.  

What Makes the Fluid Leak?

In soil, water moves from high water potential to low water potential. Similarly, there are forces inside the circulatory system that cause the transfer of fluid between capillaries.  Your blood vessels have a certain amount of pressure that is generated by your heart.  If your blood pressure goes up, it can cause edema. Dr. Stuart Campbell says, “The actual fluid pressure is part of what decides how much fluid is pushed out, but it’s not that simple. Your blood has large proteins that are too big to get out of the capillary. That means the more water that leaves the capillary and moves into the tissue, the more concentrated those proteins become, which lowers the water potential (or osmotic potential) of the blood. This delicate balance is what prevents too much water from leaking out.  However, if you have a disease that tips this balance, either through high blood pressure or a condition that allows those proteins to leak out of the capillary, edema would occur because you don’t have the osmotic potential pulling the water back into the capillary and keeping the proper balance.”

Stuart Campbell operating on the heart for a medical procedure

Dr. Campbell thought it would be interesting to figure out if he could monitor the edema of heart tissue during one of the procedures.

The Heart Experiment:

Dr. Campbell decided to see if a soil sensor would work to measure animal tissue when he was working as a summer student in the Visible Heart Lab at the University of Minnesota.  Campbell says, “Similar to a human heart transplant, this lab is able to keep pig hearts alive outside the body.  The problem, however, is that they use a manmade solution instead of blood, and that imitation blood is not ideal. If the composition of the fluid is not perfectly adjusted, you can have problems with your experiments.  I thought it would be interesting to figure out if we could monitor the edema of the heart tissue during one of the procedures. I hooked up the soil probe and used it in one experiment where I put it in contact with the heart while it was beating.  There was, in fact, a change in output of that signal during the experiment.  But, because I only got one chance at it, it was inconclusive as to whether this was indicative of an imbalance in the composition of our artificial blood substitute.”  

An Anecdotal Experiment:

Still curious to see if the idea would work, Dr. Campbell decided to try one more experiment: this time on his wife who was experiencing edema symptoms after childbirth.  He says, “It occurred to me that this was an opportunity to try out the soil moisture probe one more time to measure tissue edema.  So each day, I would measure her ankles, putting the probe in flat contact with her skin while tightening a strap gently.”  Dr. Campbell says he watched the swelling go down as the numbers on the probe got smaller, and comments, “It was anecdotal evidence that at least in extreme cases, you might be able to get the soil probe to work.  But I still have questions, such as, how would you make sure that the probe was always touching the skin in the same way?  And, if the person got sweaty, would that change the soil probe reading?”  

Nurse measuring heart rate

There are millions of people in this country who have heart failure.

Why the Experiments Should Continue:

Though Dr. Campbell hasn’t had time to pursue the experiment further, he feels that if the idea works, it has the potential to improve lives and save our nation billions of dollars.  He says, “There are millions of people in this country who have heart failure.  Maybe they’ve had a blockage in one of their coronary arteries, or perhaps their heart is worn out because of age. You can tell when someone is in heart failure because when they lie down to go to sleep at night, all that fluid makes its way slowly from the ankles, through the legs, the torso, and eventually into the chest. The problem is that the lungs are very delicate, and when you have edema in the lungs, it’s almost like you have pneumonia.  This type of sensor could be an easy way for people to monitor themselves and manage their fluid intake and diet after they get home from the hospital.”  Dr. Campbell says this helps the economy because if people don’t manage their fluids, they have to return to the hospital so they can be supervised to eat correctly and regain the proper fluid balance. This ends up costing the economy billions of dollars unnecessarily.  He concludes, “Perhaps people just need to follow instructions, but it’s possible with better monitoring that the situation can be improved.”

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Jan 1

Environmental Biophysics: Top Five Blog Posts in 2015

In case you missed our best blogs, below are the five most-viewed Environmental Biophysics posts in 2015.

Sunflowers in a sunflower field

Sunflower field in Hokkaido

Do the Standards for Field Capacity and Permanent Wilting Point Need to Be Reexamined?

We asked scientist, Dr. Gaylon S. Campbell, which scientific idea he thinks impedes scientific progress.  Here’s what he had to say.

Pine tree branch

Conifer

Environmental Biophysics Lectures

During a recent semester at Washington State University, a film crew recorded all of the lectures given in the Environmental Biophysics course. The videos from each Environmental Biophysics lecture are posted here for your viewing and educational pleasure.

Cherries on a cherry tree

Cherries

Sensor Data Improves Cherry Production

Dr. Khot and his postdoc, Dr. Jianfeng Zhou, are using leaf wetness sensors to determine if and how long water is present on cherry tree canopies after a rain event. Dr. Khot hopes that data from these sensors will help growers decide whether or not it makes sense to fly helicopters in order to dry the canopies.

Maple leafs on a maple tree

Maple leaf

What is the Future of Sensor Technology?

Dr. John Selker, hydrologist at Oregon State University and one of the scientists behind the Trans African Hydro and Meteorological Observatory (TAHMO) project, gives his perspective on the future of sensor technology.

Wet rocks on a riverbank with water flowing down through

Riverbank

Sensors Validate California Groundwater Resource Management Techniques

Michelle Newcomer, a PhD candidate at UC Berkeley, (previously at San Francisco State University), recently published research using rain gauges, soil moisture, and water potential sensors to determine if low impact design (LID) structures such as rain gardens and infiltration trenches are an effective means of infiltrating and storing rainwater in dry climates instead of letting it run off into the ocean.

Looking up at a tree canopy

Looking up at a tree canopy

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Dec 4

Understanding the Influence of Coastal Fog on the Water Relations of a California Pine Forest

Forests along the California coast and offshore islands experience coastal fog in summer, when conditions are otherwise warm and dry. Since fog-water inputs directly augment water availability to forests during the dry season, a potential reduction of fog due to climate change would place trees at a higher risk of water stress and drought-induced mortality.  Dr. Sara Baguskas completed her Ph.D. research in the geography department at UC Santa Barbara on how variation in fog-water inputs impact the water relations of a rare, endemic tree species, Bishop pine, located on Santa Cruz Island in Channel Islands National Park. The goal of her study was to enhance our ability to predict how coastal forests may respond to climate change by better understanding how fog-water inputs influence the water budget of coastal forests.

Fog on Trees

Dr. Baguskas’ study seeks a better understanding of how fog-water inputs influence the water budget of coastal forests.

Fog Manipulation

Santa Cruz Island supports the southern extent of the species range in California, thus it is where we would expect to see a reduction in the species range in a warmer, drier, and possibly less foggy future. To advance our mechanistic understanding of how coastal fog influences the physiological function of Bishop pines, Dr. Baguskas conducted a controlled greenhouse experiment where she manipulated fog-water inputs to potted Bishop pine saplings during a three-week drydown period. She installed soil moisture (VWC) sensors horizontally into the side of several pots of sapling trees at two different depths (2 cm and 10 cm) and exposed the pines to simulated fog events with a fog machine.

In one group of plants, Baguskas let fog drip down to the soil, and in another treatment, she prevented fog drip to the soil so that only the canopies were immersed in fog.  She adds, “Leaf wetness sensors were an important complement to soil moisture probes in the second treatment because I needed to demonstrate that during fog events, the leaves were wet and soil moisture did not change.” Additionally, Baguskas used a photosynthesis and fluorescence system to measure photosynthetic rates in each group.

Fog in pine trees from the ground

The fog events had a significant, positive effect on the photosynthetic rate and capacity of the pines.

Results

Dr. Baguskas found that the fog events had a significant, positive effect on the photosynthetic rate and capacity of the pines.  The combination of fog immersion and fog drip had the greatest effect on photosynthetic rates during the drydown period, so, in essence, she determined that fog drip to the soil slows the impact of drydown.  

“But,” she says, “when I looked at fog immersion alone, when the plant canopies were wet by fog with no drip to the soil, I also saw a significant improvement in the photosynthetic rates of these plants compared to the trees that received no fog at all, suggesting that there could have been indirect foliar uptake of water through these leaves which enhanced performance.”  An alternative interpretation of that, Baguskas adds, is that nighttime fog events reduced soil evaporation rates, resulting in less evaporative loss of soil moisture.

Dr. Baguskas says her “canopy immersion alone” data are consistent with other research: Todd Dawson, Gregory Goldsmith, Kevin Simmonin, Carter Berry, and Emily Limm have all found that when you wet plant leaves, it has a physiological effect, suggesting the plants are taking water up through their leaves and not relying as much on soil moisture.  (These authors performed different types of experiments, but their papers serve as reference studies). Baguskas says, “My results suggest that is what’s going on, but it’s not as definitive as other studies that have actually worked on tracking the water through leaves using a stable isotope approach.”  

Lessons Learned

Though Dr. Baguskas did not monitor soil temperature in this study, she says that in the future, she will always combine temperature data with soil moisture data.  She comments, “Consistently, the soil moisture in the “canopy-immersed only” plants was slightly elevated over the soil moisture in the control plants.  It made me wonder if this was a biologically meaningful result. Does it support the fact that if plants are taking up water through their leaves, they don’t rely on as much soil moisture?  Or did my treatment change soil temperature, and is that having a confounding effect on my results?  What I’ve learned from this, is that in the future I will always use soil probes with temperature sensors because you may not know until you see your results if temperature might be important.”

Future Fog Studies

Baguskas is a USDA-NIFA postdoctoral Research Fellow working with Dr. Michael Loik in the Environmental Studies Department at UC Santa Cruz. She continues to study coastal fog, but now in strawberry fields. Her current research questions are focused on integrating coastal fog into water-use decisions in coastal California agriculture. She loves the work and continues to rely on soil moisture sensors to make meaningful and reliable environmental measurements in the field and greenhouse.

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Nov 19

Killing Cheatgrass and Shooting for the Moon

My grandfather, Grant A. Harris, wrote his Ph.D. thesis about the detrimental effects of cheatgrass (bromus tectorum) on rangeland ecology, so I’ve been taught since birth to hate this invasive plant species. So it didn’t surprise me to read that cheatgrass has become the equivalent of an eco-supervillain, wreaking havoc in farmer’s fields, rapidly spreading, and reducing wheat yield—sometimes by fifty percent.  

Microscope focusing on glass panel with sample on it

Washington State University scientist, Dr. Ann Kennedy, has successfully worked with a naturally-occurring soil bacteria that limits the depth of root growth in cheatgrass.

Cheatgrass increases the spread of wildfire, aiding the jump from plant to plant, and it afflicts livestock: lodging in the eyes and mouths of grazing cattle, not to mention having little nutritional value. For years, it’s been tenacious and incredibly prolific, out-competing native grasses and essentially “taking over” the eco-world.  Until now.  This New York Times article spotlights Washington State University scientist, Dr. Ann Kennedy, and her successful work with a naturally-occurring soil bacteria that limits the depth of root growth in cheatgrass, reducing its competitive advantage on the prairie.  

As a scientist, I was intrigued by this article because of what it didn’t say.  Dr. Kennedy, a good friend of mine and a great scientist, once told me that her bacteria experiment was the one she thought least likely to work. She’d looked at it as a kind of “shoot the moon” idea, riddled with “unknowns,” making it risky to spend too much time on.  In fact, she’d only had time to pursue this interesting and challenging experiment because she’d made time for it.

A concentrated solution of bacteria being sprayed on cheatgrass

A concentrated solution of bacteria is sprayed on fields, and over time, the organisms colonize the roots of the cheatgrass.

In a seminar she gave years ago about her work with cheatgrass, Dr. Kennedy shared her simple 60-30-10 prioritization method.  Sixty percent of her research effort was put into core projects she knew would yield publishable papers and keep her lab running.  Thirty percent of her time was spent on challenging projects that were more impactful but less likely to succeed. Finally, she put ten percent of her effort into “shoot the moon” type projects: research that was unlikely to come to fruition, but if successful, would have a dramatic impact in the world.  

In science, it’s easy to get stuck in the purely practical, only spending time on the experiments we know will work. It’s safer and won’t expose us to ridicule when things don’t go the way we hope. But, Dr. Kennedy has proven that there is value in trying things that might fail.  

It’s been more than a decade since I’ve listened to her lecture, but it still impacts the way we do research at METER. Although we spend a lot of time on projects we know will turn into finished instruments, we continue to dream up ways to produce frozen soil moisture release curves or measure leaf water potential. These ideas may not succeed, but if they do, they could have a big impact on the way we make measurements.

As I think about my team’s research priorities and the possibilities of success, I always first consider core projects: What are we really good at?  What will be a sure bet for success?  But because of Dr. Kennedy, I’ll always devote some of my time to more risky endeavors, speculating on what could happen and what might possibly change the world.  

(Read about our most spectacular example of risky research:  the collaboration with NASA’s Jet Propulsion Laboratories to send one of our sensors to Mars.)

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Nov 14

Sensor Data Improves Cherry Production

In July of 2013, Lav Khot and his team were in the field looking at how cherries were picked, weighed, and transported, when suddenly a helicopter began circling around a nearby orchard block.  When Dr. Khot asked the grower about it he said, “There was a rain last night, and we are trying to dry the tree canopies.” The grower told Khot that cherries are susceptible to cracking if moisture stays on the fruit too long, so they hire helicopters to fly over their orchards to remove water from the fruit and leaves, hoping to prevent fruit loss.

Bright red cherries on a tree

The economic impact of solving the cherry cracking problem could be huge as growers now suffer heavy losses each year.

Fresh market cherries are a lucrative business. That’s how the growers can afford the approximately $25K it costs to rent the helicopters every season. They try to do everything that they can to stop any cracking or splitting, but interestingly, Dr. Khot says grower decisions are influenced completely by emotion. “If there is a rain event, the farmer will become anxious, and they will hire pilots to fly the helicopter.”  

Dr. Khot wondered if he could help the cherry growers make their decisions based on real data instead. He and his postdoc, Dr. Jianfeng Zhou, are using leaf wetness sensors to determine if and how long water is present on the tree canopies after a rain event. Dr. Khot hopes that the data from these sensors will help growers decide whether or not it makes sense to fly the helicopter.

Why the cherries split

Not all varieties of cherry crack, but high sugar content varieties do as the skin is thin during maturation.  There are two hypotheses associated with fruit splitting or cracking:

Irrigation:  High water availability in the soil as the fruit is maturing (a few weeks before harvest) encourages trees to take up more water and causing the fruit to split.

Rainwater:  Rain collects in the cherry stem bowl or hangs off the bottom and is slowly absorbed into the fruit along the osmotic potential gradient. The fruit will start to split due to increased pressure inside the skin.

Dr. Khot and his team will use soil moisture sensors to investigate the first hypothesis with the object of improving irrigation management, especially as harvest approaches.  And he’s getting some support:  “Dr. Matt Whiting (colleague at the Center for Precision and Automated Agricultural Systems, Washington State University) is helping us understand this cracking phenomenon from the soil perspective. He is doing work on deficit irrigation (reducing the rate of irrigation below optimal) towards harvest time and seeing how that relates to cracking.  Also, the WSU CAHNRS ERI (Emerging Research Issues grant), which supports high-risk research, has funded us $75,000, along with Decagon who is supporting us with their sensors.”

Last Year’s Research

There are two approaches to drying canopies. One uses a sprayer that produces a cross-wind that moves sideways through the canopies, while the other uses the downwash from helicopter blades.  Last year, Dr. Khot and his research assistant experimented with crosswind velocities to see how much wind was being generated and how much water was really being dispersed.   Dr. Khot commented, “Last season we went out to the WSU orchard and ran the sprayer at two settings in order to see how water was removed and how much wind was coming through the canopies for a given amount of time.” They had good success at both removing the water from the trees and measuring it with the leaf wetness sensors.  But, they started the measurements after the cherries had matured, so weren’t able to tie it to cracking.

This Year’s Experiment

One issue with using helicopters is that they are extremely dangerous.  Accidents are not uncommon, and unfortunately pilots have died.  This year the team will also evaluate the efficacy of a mid-size, unmanned helicopter in order to test if it can produce enough downwash to dry the cherries and compare it with manned helicopters.  Dr. Khot says, “The helicopters are large and difficult to fly close to the canopies, but we can program the unmanned drone to fly close to the canopy and get rid of the water safely.” Digital Harvest and Yamaha, who are supporting this aspect of the research, have received an exemption from the FAA so they can test their unmanned helicopter.

Differing Tree Architectures

Dr. Khot’s team did their first experiments on traditional cherry tree architectures (imagine a typical tree), but this year they will perform their experiments on trees that are trained into a “Y” shape, or completely vertical.

Cherry production trees

These trees represent traditional tree architecture, but this year researchers will perform their experiments on trees that are trained into a “Y” shape, or completely vertical.

Researchers have developed these new architectures for ease of harvesting and management, but Dr. Zhou says that there will be less canopy variability and thus more interpretable results compared to the traditional tree architecture where wind velocity is more heterogeneous throughout the canopy.

Economic Impact  

Dr. Khot says the economic impact of solving the cherry cracking problem could be huge as growers now suffer heavy losses each year.  One former grower underscored this when he noted they lost one crop in every four. But, there could be other benefits as well. The implications of this research could lead to solving other grower problems such as disease and pest management.   “WSU already has a good AgWeatherNet program where we monitor the weather outside the trees at different locations, but not inside the canopies. If we had some smart sensing equipment like the leaf wetness sensor sitting in the canopy monitoring the wetness level over a 24-hour cycle, then we could develop some models based on the wetness and relate them to the number of pests at different locations in the orchard.  That is something every grower can benefit from.”

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

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

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Nov 13

Will Sample Disturbance Lead to Lower Accuracy?

Sampling soil for laboratory analysis of water potential is done for two basic reasons.  The simplest is to determine the current water potential of the soil.  The other is to determine the moisture release curve of the soil.  Regardless of the reason for measurement, the question of sample disturbance is important to ensure an accurate result.  Dr. Colin Campbell explains why:

researcher hand holding soil

Soil is disturbed when it’s removed from its natural structure.

Water Potential and Pore Size:

In soil samples, the void spaces (pores) in between soil particles can be simplistically thought of as a system of capillary tubes, with a diameter determined by the size of the associated particles and their spatial association.  The smaller the size of those tubes, the more tightly water is going to be held because of the surface association.  

In a clay, water will be held more tightly than in a sand at the same water content because clay contains smaller pores and thus more surface area for the water to bind to. But, even sand can eventually dry to a point where there is only a thin film of water on its surfaces and water will be bound tightly.  In principle, the closer water is to a surface, the tighter it will be bound.

Sample Disturbance

Sample disturbance (disturbing soil pores when you remove a sample from the ground) becomes an issue depending on the water potential of your sample. Typically, the less negative (wetter) the water potential, the larger impact sample disturbance will have on the measurement.  We can do a calculation that shows there are specific pore sizes associated with specific water potentials (see table 1).

Water potential units diagram

If you disturb a sample with low water potential, permanent wilting point (-1.5 MPa) for example, the pores that are still filled with water would be approximately 0.2 um in diameter, far too small to be broken apart by scooping up a sample.  Thus, we could reasonably assume that your WP readings won’t be affected much.  But if you disturb soil with higher water potential, say field capacity (-0.033 MPa), it’s much more likely that water will be disturbed, as it fills pores to approximately 9 um.    

Hygrometers

Still, this is only an issue if you are attempting to measure in a high WP range.  If your chilled-mirror hygrometer only measures up to -1000 kPa, sample disturbance will not be an issue because those pores that will have broken will likely be larger than the sub-micrometer that are holding water, which is beyond the accuracy of your instrument.   However, some hygrometers can now measure to an upper limit of -100 kPa, which approaches the point where sample disturbance will make a difference.  

Tensiometers

If you are sampling to measure with a tensiometer (measures 0 kPa to -80kPa), it’s extremely important to keep your samples intact because tensiometers cover the emptying range of the largest pores found in soil.  A soil collar (sample ring) pounded into the ground will yield the most intact soil core.  It’s the best method to use if you need make sure soil pores remain undisturbed to yield an accurate water potential measurement.

For a more in-depth examination of the magnitude of the effects of sample disturbance, read this chilled-mirror hygrometer App Note detailing the subject.

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

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

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