Skip to content

Posts tagged ‘soil moisture’

Jul 25

1 Comment

Which Factors Make Rain Gardens More Effective? (Part 2)

Scientists often evaluate Low Impact Development (LID) design by quantifying how much stormwater rain garden systems (cells) can divert from the sewer system.  But Dr. Amanda Cording and her research team want to understand what’s happening inside the cell in order to improve the effectiveness of rain garden design (see part 1).  Below are the results of their research.

Picture of yellow flowers

Deep rooted systems were found to have a much better ability to hold the soil in place and remove nutrients.

Key Findings

Cording says that some of her key findings were that the soil media and vegetation selection is absolutely crucial to the performance of these systems. Cording’s team looked at the root layering perspective in three dimensions and found that deep rooted systems were found to have a much better ability to hold the soil in place and remove nutrients throughout the life cycle of the cell. The more surface area the roots covered, the more pollutants the cell would remove.  She adds, “Cells with deep-rooted plants were found to be resilient during increased precipitation due to climate change, did well at retaining peak flow rates, and performed well at removing total suspended solids and nutrients predominantly associated with particulates.”  Labile nutrients, Cording says, were a completely different story. She says the bioretention systems have to be specifically designed to remove  those nutrients through sorption (P) and denitrification (N).

Researcher holding dirt in cupped hand

Compost was found to have a negative effect on water quality.

Compost, which is often used as an organic amendment in the soil media to help remove heavy metals and provide nutrients for the plants, was found to have a negative effect on water quality overall, due to the high pre-existing labile N and P content. She says, “It’s intuitive, but at the same time, a lot of these systems are designed based on bloom time and color, and not necessarily on the physical and chemical pollutant removal mechanisms at work.”

Green algal bloom in a freshwater lake

Green algal bloom in a small freshwater lake in New Zealand. (Image: Massey University)

What Lies Ahead?

Cording also tested a proprietary bioengineered media in two of her cells which was designed to remove the phosphorous that causes algal blooms in the rivers and streams.  She says, “It did a phenomenal job. There was very little phosphorous coming out compared to the traditionally-designed retention cells.  Cording, who is now based in Honolulu and works for an ecological engineering company called EcoSolutions, is looking at how to use natural, highly-leached iron rich soils, to get a similar amount of phosphorous removal, and how bioretention can be designed with anoxic storage zones to remove nitrate via denitrification. She says, “These nutrients can be easily removed from stormwater with a little conscious design effort and a splash of chemistry.”

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

Get more information on applied environmental research in our

LinkedInMessengerRedditThreadsCopy

Jul 15

1 Comment

Which Factors Make Rain Gardens More Effective?

Low Impact Development (LID) is an approach to development (or re-development) that mimics pre-development hydrology and uses ecological engineering to remove pollutants in stormwater and wastewater so it can be reused or replenish groundwater supplies. Examples of LID features include porous pavement, constructed wetlands, green roofs, and rain gardens. LID stormwater bioretention systems such as rain gardens have been proven to work, but are they designed as effectively as they could be?  Dr. Amanda Cording (formerly at the University of Vermont) and her team wanted to understand which design factors would make rain gardens more resilient, increase phosphorus adsorption, and reduce nitrates.

Rain Garden aerial view

Cording and her team wanted to understand what was happening inside bioretention cells.

What’s Happening Inside?

Scientists often evaluate LID design by quantifying how much stormwater the systems (cells) can divert from the sewer system.  But Cording and her team wanted to understand what was happening inside the cell.  They wondered which types of soil media and infrastructure would optimize a stormwater bioretention system’s ability to improve water quality.  She says, “We wanted to gather water quality information coming in and going out of the system. I designed inflow and outflow monitoring infrastructure to measure nutrient and sediment pollution.”   The system monitored pollution by sampling stormwater runoff from a paved road surface before and after it went through bioretention cells. Each cell was constructed with different features to test the influence of vegetation and soil media on pollutant removal capabilities.

Bioretention cells diagram

Bioretention cells at the newly constructed Bioretention Laboratory at the University of Vermont.

Methods Used

To understand what was happening within eight bioretention cells at the newly constructed Bioretention Laboratory at the University of Vermont, Dr. Cording and her team investigated the mechanisms influencing greenhouse gas emissions and nutrient transformations at various depths in engineered soil media. In addition to using her own monitoring infrastructure, Dr. Cording used soil moisture sensors to measure water content within the soil media. She says, “I was comparing different vegetation treatments while simulating increased precipitation due to climate change in the Northeast.  I put the soil probes in at 5 cm and 61cm, one on top of the other.  Then I looked at the way the EC and the volumetric water content (VWC) changed prior to a storm event, during a storm event, and after a storm event.”

Garden in bloom in the rain

One of the team’s bioretention cells at the University of Vermont.

Cording says the EC and VWC sensors allowed them to get a general sense of what was happening inside the cell over time.  She adds, “I used the data when I needed to know more of the story, such as how the conductivity at the surface compared to other depths so we could see if the nutrients in the soil were migrating, and how much was moving down.  We were also able to use the sensors to compare the VWC around the roots of different vegetation types. It provided a lot of insight into the dynamic world that exists below the soil surface.”

Next Week:  Read about the team’s key findings and what lies ahead for this research.

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

Get more information on applied environmental research in our

LinkedInMessengerRedditThreadsCopy

Jul 8

Improving Drought Tolerance in Soybean

Limited water availability is a significant issue threatening the agricultural productivity of soybean, reducing yields by as much as 40 percent. Due to climate change, varieties with improved drought tolerance are needed, but phenotyping drought tolerance in the field is challenging, mainly because field drought conditions are unpredictable both spatially and temporally.  This has led to the genetic mechanisms governing drought tolerance traits to be poorly understood. Researcher Clinton Steketee at the University of Georgia is trying to improve soybean drought tolerance by using improved screening techniques for drought tolerance traits, identifying new drought tolerant soybean germplasm, and clarifying which genomic regions are responsible for traits that help soybeans cope with water deficit.

Seedlings sprouting

Researchers are trying to improve soybean drought tolerance by using better screening techniques for drought tolerance traits.

Which Traits Are Important?

Clinton and his colleagues are evaluating a genetically diverse panel of 211 soybean lines in two different states, Kansas and Georgia, for over two years to help him accomplish his research objectives. These 211 lines come from 30 countries and were selected from geographical areas with low annual precipitation and newly developed soybean lines with enhanced drought-related traits, along with drought susceptible checks. The researchers are looking at traits such as canopy wilting.  Some plants will take a few days longer to wilt, allowing these plants to continue their photosynthetic ability to produce biomass for seed production. Other traits that he is interested in evaluating are stomatal conductance, canopy temperature with thermal imaging, relative water content, and carbon isotope discrimination.

Beans growing on a stalk

The scientists want to monitor traits such as canopy wilting.

Use of Microclimate Stations to Monitor Environmental Conditions

Clinton says to make selection of drought-tolerant lines easier and more predictable, knowledge of field environmental conditions is critical. He says, “You can phenotype all you want, but you need the true phenotype of the plant to be observed under real drought conditions so you can discover the genes for drought tolerance and improve resistance down the line in a breeding program.”

In addition to soil moisture sensors, the team used microclimate weather stations to help monitor water inputs at their two field research sites and determine ideal time periods for phenotyping drought-related traits.  Steketee says, “We put microenvironment monitors in the field next to where we were growing our experimental materials.  Both locations use those monitors to keep an eye on weather conditions throughout the growing season, measuring temperature, humidity, and precipitation. Since we could access the data remotely, we used that information to help us determine when it was time to go out to the field and look at the plots. We wanted to see big differences between soybean plants if possible, especially in drought conditions. By monitoring the conditions we could just go back to our weather data to show we didn’t get rain for 3 weeks before we took this measurement, proving that we were actually experiencing drought conditions.”

Soybeans

The team identified some lines that performed well.

Results So Far

Though 2015 wasn’t a great year for drought in Georgia, Clinton says there was a period in late July when he was able to measure canopy wilting, and they identified some lines that performed well.  He says, “We compared our data to the data collected by our collaborator in Kansas, and there are a few lines that did well in both locations.  Hopefully, another year of data will confirm that these plants have advantageous drought tolerance traits, and we’ll be able to probe the advantageous traits out of those lines and integrate them into our breeding program.”

Future Plans

The team will use what’s called a genome-wide association study approach to identify genomic regions responsible for drought tolerance traits of interest. This approach uses phenotypic information collected from the field experiments along with DNA markers throughout the soybean genome to see if that marker is associated with the trait they are interested in.  If the scientists find the spot in the genome that is associated with the desired trait, they will then develop genomic tools to be used for selection, integrate that trait into elite germplasm, and ultimately improve the drought tolerance of soybeans.

See weather sensor performance data for the ATMOS 41 weather station.

Explore which weather station is right for you.

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

Get more information on applied environmental research in our

LinkedInMessengerRedditThreadsCopy

Jun 24

1 Comment

Lysimeters Determine If Human Waste Composting Can Be More Efficient (Part 2)

In Haiti, untreated human waste contaminating urban areas and water sources has led to widespread waterborne illness.  

Hospital rooms in Haiti with patients infected with cholera

Waterborne disease is the leading cause of death for children under 5. Currently, Haiti is battling the largest cholera outbreak in recent history. Over 1/6 of the population is sickened to date.

Sustainable Organic Integrated Livelihoods (SOIL) has been working to turn human waste into a resource for nutrient management by turning solid waste into compost.  (See part 1).  

Water ways infected with waste and trash

Contaminants making their way into the waterways.

The organization plans on performing experiments with lysimeters, to determine if human waste will contaminate Haitian soil during the composting process.

A river infected with waste right below a huge forest

Even in places where there are toilets, they are often poorly designed or poorly placed. This latrine is located just above a river, where people are getting their bathing and drinking water.

Lysimeters Help Assess Health Hazards

SOIL will use G3 passive capillary lysimeters in an experiment to determine if composting human waste without a barrier between the waste and the soil will result in ecological and/or health hazards.  Why? The problem is “jikaka,” or “poo juice.”  The compost facility currently redistributes it onto the compost and finishing piles, but they would rather not have to manage it. They believe if they remove the concrete slab and allow composting to occur in contact with soil, the composting process will be easier and faster.

Mounds of dirt behind a tree

SOIL’s agricultural team conducts studies on the use of compost to improve farming practices and maximize economic benefits of targeted compost application.

The Experiment

The organization will test their idea as they expand their facility. New compost bins and staging areas for finishing have been built absent concrete pads. G3 passive capillary lysimeters have been installed, three beneath the compost bin, and four beneath the first staging area for finishing. They will be used to monitor the amount of moisture (jikaka) that travels through the soil as well as check for anything harmful that travels with it.

Children holding soil in their hands

SOIL’s human waste compost was found to increase sorghum yields by 400%.

What’s the Future for Konpòs Lakay?

SOIL’s agricultural team studies the use of their compost (Konpòs Lakay) in order to optimize farming practices and the economic benefits of targeted compost application. The data they collect will help them expand the market for Konpòs Lakay, which in turn will support the sustainability of SOIL’s sanitation programs.

For more information on SOIL’s waste treatment efforts, visit their website, or watch the video below, a TEDx talk given by SOIL co-founder, Sasha Kramer.

Discover G3 Drain Gauge passive capillary lysimeters→

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

LinkedInMessengerRedditThreadsCopy

Jun 11

Founders of Environmental Biophysics: Champ Tanner

Champ Tanner

Champ Tanner (November 16, 1920 – September 22, 1990) Image: soils.wisc.edu

We interviewed Gaylon Campbell, Ph.D. about his association with one of the founders of environmental biophysics, Champ Tanner.

Who was Champ Tanner?

Champ Tanner was a dominant scientist in his time and a giant among his colleagues.  He was the first soil scientist to be elected a member of the National Academy of Sciences: the highest honor a scientist can achieve in the United States.  Some may not realize that throughout a career filled with achievements and awards, he battled the challenges of a debilitating illness.  He didn’t let that limit his passion for science, however.  His efforts to understand and improve measurements generally went beyond those of his fellow scientists.  One of his colleagues once said of him, “Champ’s life exemplified goal-oriented determination and optimism regardless of physical or financial impediment.”

Green wheat stalks

Dr. Tanner was one of the pioneers in applying micrometeorology to agriculture.

What were his scientific contributions?

Champ was an extremely careful experimentalist who was gifted at developing instrumentation.   He started out making significant contributions in soil physics such as improved methods for measuring water retention, particle size distribution, air-filled porosity, and permeability.  He was one of the pioneers in applying micrometeorology to agriculture and was passionate about finding ways to improve the precision and reliability of measurements.  No measurement was too difficult.  He designed and built his own precise weighing lysimeters which provided measurements of evapotranspiration in as little as 15 minutes.   Later, he switched to plant physiology, reading almost every published paper on the subject and then building his own thermocouple psychrometer and plant pressure chambers, making important contributions in that field.

His largest contribution, however, was the measure of excellence he inspired in the students that he trained.   I don’t know of anybody, anywhere in the world, that produced a crop of students that has attained the levels that his have.  They’ve all made enormous contributions in many different fields.  Perhaps it was because he was a pretty hard taskmaster.   He expected the students to meet a standard, and the ones that struggled with that had a hard time. In fact, to this day one former student complains, “About once a year, I have a nightmare in which Champ appears.”

Boy walking through a library

I don’t know of anybody, anywhere in the world, that produced a crop of students that has attained the levels that his have.

Champ wanted his students to measure up, but he also cared about them.  His fellow scientist, Wilford Gardner, described him this way, “There was a transcendent integrity to his personality that permeated everything he did.  He could be blunt, candid and forthright, but he was never lacking in compassion and concern for students, colleagues, and friends.”

What was your association with him?

I had a wonderful relationship with Champ, although I wasn’t one of his students. One of his former students came to WSU as a visiting scientist and told him about what I was working on.  As a result, he brought me into his inner circle of associates and played a vital role in the success of my research.  This association even extended to my family who were with me on one of my many trips to Madison. Despite my numerous and occasionally unruly progeny, he and his wife welcomed us like long lost relatives and made each of the children feel special.  That’s who they were: the most caring and outgoing people.

Champ also had a sense of humor.  He used to call me up to have long discussions about science, and because he was two time zones ahead, it would get pretty late for him. We’d be having an intense discussion about experimentation, and all of a sudden he’d stop and say, “Oh, I’d better cut this off, or I’ll get home to a cold supper and a hot wife.”

What kind of a person was he?

If you worked in his lab, you needed to tow the mark.  You didn’t leave tools around, and you didn’t mess them up. If you left out a screwdriver, you’d find it on your desk the next morning with a terse note.  And if you took the diagonal pliers, cut some hard wire with it and left some nicks, those would be on your desk too. It was a sort of tough love, but he used it to train his students to the highest possible level.  

Researcher looking through a microscope

He taught his students to be rigorous in their measurement protocols

He wanted his students to stand up and argue for their point.  If you were the kind of person that could stand your ground and put up a good defense, he loved that.  Gardner described Champ in this way, “His work hours were legendary.  His standards of science and personal integrity were almost unrealistically high.  The stories his students now pass on to their students may sound apocryphal to those who did not know Champ.  But it was impossible to exaggerate where Champ was concerned.”

What do you think scientists today can learn from him?

What we can learn from Champ Tanner is not to fool ourselves.  He thought you should try to come to an answer in a few different ways, to be sure that it really was the answer. He taught his students to be rigorous in their measurement protocols in order to get the noise out of their experiments.  He wanted them to dig to the bottom of problems and understand the details.  In his mind, you couldn’t be a scientist and rely on somebody else to figure out heat transfer or radiation. He thought you should understand it well enough that you could defend it yourself.   

You can read more about Champ Tanner’s life and scientific contributions in this biographical sketch, written for the National Academy of Sciences when he died.

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

Get more information on applied environmental research in our

LinkedInMessengerRedditThreadsCopy

Jun 3

1 Comment

Are Biodegradable Mulches Actually Better for the Environment? (Part II)

In a continuation of last week’s post, Henry Sintim, PhD student at Washington State University is investigating whether biodegradable mulches are, in fact, what they claim to be (see part I).

Resercher gathering data from an installation site

Lysimeter readings revealed higher EC measurements.

Leaching

Sintim and his team want to understand what’s leaching through the soil as the mulches degrade.  He installed passive capillary lysimeters at a 55 cm depth to collect leachate samples for analysis of BDM particulates.  He was surprised when the lysimeter readings revealed higher EC measurements. However, the EC in the PE, paper mulch, and no-mulch treatments were also high, hence that could be due to the leaching of accumulated salts in the soil surface. He says, “We have yet to examine the leachate samples for the presence of particulates.”   

Researchers installing lysimeters

Installing lysimeters

Composting Alternatives

If the team finds that some of the BDMs do not biodegrade very well in the field, the alternative could be on-farm composting, which would be more viable than having to deal with polyethylene plastic.  Sintim and his research team have set up a composting study where they have been digitizing the images of the mulches degrading.  He adds, “We buried the mulches in a mesh bag, and periodically we retrieve the bags to study the mulch. There was some black staining on the mesh bag, which we suspect is a nanoparticle called, “carbon black,” used as reinforcing filler in tires and other rubber products.

Scientist studying how mulches degrade over time

The team buried the mulches in compost, and periodically they retrieve the mesh bags to study the mulch.

Sintim says the manufacturers do not disclose the actual constituents of their mulches, so he has arranged to examine the mesh bags with WSU’s scanning electron microscope in order to confirm that the stains were due to the presence of particulates. Sintim confirmed that carbon black was used in their experimental BDM, but they don’t know whether the carbon black was made from petroleum products, as there is non-petroleum-based carbon black.  He is going to determine whether these particles leach through soil by examining leachate samples from the lysimeter. He will also perform more tests to make sure that these nanoparticles are not going to have any adverse effects on the agro-ecosystem.

What’s in the Future?

While Sintim and his colleagues have made important discoveries, there is still work to be done. He and his team are going to collect three more years’ worth of data to see if there really is a BDM that delivers on its promises and if leaching particles pose a threat to the groundwater.

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

Get more information on applied environmental research in our

LinkedInMessengerRedditThreadsCopy

May 27

1 Comment

Are Biodegradable Mulches Actually Better for the Environment?

Henry Sintim, PhD student at Washington State University, is investigating whether biodegradable mulches are, in fact, what they claim to be.

Plant row farm with dirt between each row

Application of plastic mulches conserves water, and helps in weed, pest, and disease control.

He and his research team want to understand what leaches into the soil as the mulches degrade and which ones perform as well as polyethylene-made plastic mulches (PEs) at weed, pest, and disease control.

Plastic Mulch

Application of plastic mulches in agriculture is a common practice by specialty crop producers worldwide. It conserves water, and helps in weed, pest, and disease control, subsequently improving crop yield and quality. Because PE is durable and does not degrade in the soil, you cannot leave it in the field, which ultimately leads to the question of disposal.  When PE is buried in the field, it becomes contaminated with soil and can’t be recycled but instead requires transport to a landfill, increasing production costs. Another problem arises when landfill facilities are not available. When this is the case, growers stockpile PE on their farm, where the rain can wash the mulch down to streams and water bodies. Henry Sintim and his team are investigating whether or not biodegradable plastic mulches (BDMs) could be a viable alternative.

Researchers digging a site up for installation

The team installs a lysimeter beneath the mulches.

Biodegradable Alternatives

Substituting PE with BDM could alleviate the need for disposal. However, Sintim says the potential impact on agricultural soil ecosystems needs to be assessed before adopting biodegradable mulch for field use. For instance, do biodegradable mulches really degrade?  Sintim explains, “By BDM, we mean it is plastic mulch, but it has been made from pure or partial biobased materials. Though there are plastic mulches advertised as biodegradable, none have actually been proven to biodegrade, so the team is examining degradation of different commercial BDM types over time. They have also included an experimental BDM, in which the constituents were specified by the team.”

Sintim is monitoring the degradation of BDM by assessing the material properties and measuring the particle size and surface area via photography: digitizing and analyzing them using Image J software.

Researchers standing at an installation getting data

There are indications that some of the BDMs are performing well.

How Well Do the Mulches Compare?

Sintim also wants to find out how well BDMs maintain microclimate in comparison to PE. Since soil temperature and moisture content are important parameters that govern chemical reaction rates and microbial activity, and are likely to vary among the different BDM treatments, he is monitoring soil moisture dynamics using soil moisture and temperature sensors installed at 10 cm and 20 cm depths. In addition, the team has installed sensors directly underneath the mulches to measure surface temperature and light penetration. Reduction of light penetration is the attribute that helps plastic mulches to control weeds. The team is also assessing soil quality using the USDA Soil Quality Test Kit.  

Sintim says so far one of the commercial BDMs and the experimental BDM had the same yield performance as PE.  He adds, “We don’t have final results yet, and there are a lot of variables that could come into the picture. But I will say there is an indication that some of the BDMs are performing well.”

Next week:  Find out how Sintim will determine what’s leaching into the soil and another alternative for polyethylene plastic mulch.

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

Get more information on applied environmental research in our

LinkedInMessengerRedditThreadsCopy

May 23

Building a Martian: the University Rover Challenge

One day soon robots will rule the world. Well, maybe. For now, they rule Mars as research and colonization efforts push forward, and for a few days this June they will rule the Mars Desert Research Station in Hanksville, Utah at the University Rover Challenge (URC).

Launched in 2006, the URC has hosted competitions since 2007 and boasts contestants from around the globe, including the United States, Canada, India, Bangladesh, Poland, and Egypt.  Each year, contestants are given point scores based on how quickly they complete a series of tasks and how closely each task conforms to parameters outlined by the competition guidelines.  This year, teams must complete a terrain traverse, a simulated equipment servicing, an astronaut assist, and the retrieval and measurement of a non-contaminated soil sample.

Collaboration and Challenges

Byron Cragg, Science Team Lead for the Titan Rover Team out of California State University, Fullerton, says it’s been an uphill battle. “We’ve had to design the systems we are using to control our rover, retrieve our data, and keep our data organized from the ground up.  We’ve also needed to make our rover robust in case a battery or a motor fails during the competition.” 

It is no easy feat to build a rover for the Utah desert, let alone send instrumentation to Mars. This is why it has taken a multi-disciplinary team to build the physical components, robotic arm, telecommunications, and scientific cache on Titan Rover.  Cragg says his team consists of scientists, computer engineers, electrical engineers, mechanical engineers, geologists, chemists, and biologists all working together.

A prototype of the Titan Rover

A prototype image of the Titan Rover.

Titan Rover Features

The CSU rover is outfitted with sophisticated features like Leap Motion infrared sensors that allow Titan Rover’s robotic arm to be controlled by a human counterpart moving their arm in free space. When the user moves their arm and hand position, the arm on Titan Rover is given a signal from the command center to move accordingly.

Cragg is responsible for the 3D printed science cache that uses a 3” auger and a capacitance sensor to measure a soil sample’s volumetric water content, temperature, and bulk electrical conductivity. During the competition, the team will also be required to construct a stratigraphic column from HD images transmitted by the rover, as well as measure soil temperature at a depth of 10cm.

“It comes down to designing the pieces to communicate and work together to perform the tasks correctly,” Cragg says about the challenges ahead. “It’s one thing to build the rover,” he adds, “but it’s another to complete the requirements.”

While ambitions of a colonized Mars are on the horizon and research pushes on, like the Titan Rover project, progress will require collaboration and teamwork. In the meantime, good luck to all the Earthlings who will be competing in the Utah desert this June.

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

Get more information on applied environmental research in our

LinkedInMessengerRedditThreadsCopy

Apr 29

Does Early Planting Increase Risk to Winter Canola?

Many dryland winter canola growers assume that if they plant earlier, they will establish a stronger plant, but Washington State University researcher Megan Reese recently found that this was not the case.  She and her team discovered that planting earlier increases risk to the plant, as more water is used, and the reduced amount of water then left after the winter season limits spring regrowth. Megan’s findings could be valuable as water is the most yield-limiting factor in eastern Washington state’s wheat-dominated dryland systems, where winter canola has newly emerged as a rotational crop.

Bright yellow canola field in full bloom

Winter canola is cold hardy, but it’s not as resilient as wheat.

Early Planting:

Winter canola is cold hardy, but it’s not as resilient as wheat.  It’s planted in August, much earlier than winter wheat, which is planted in the late fall.  In order to survive, winter canola has to establish a hardy taproot system so that plants have reserves to survive the winter. Megan says, “Opinions vary, but anecdotally, a dinner plate sized plant can survive winter fairly well, so that’s why winter canola is planted in August . However, because establishment and germination can be an issue, we decided to try planting in June at Ritzville, Washington, thinking the soil would be more moist and have a cooler seedbed.  However, the early planting date had a negative effect on winter survival. Not one of the early plants survived.  We found the plants that started earlier used a lot more water, and consequently, the winter rains weren’t enough to refill the soil profile.  Excessive growth and bolting also contributed to low survivorship.”

Methods and Moisture Release Curves:

Megan monitored soil water in the profile several different ways.  At one location she used a neutron probe and hand-sampled gravimetric soil moisture in the top 30 cm of the profile, and in other locations, she was limited to  hand samples.  Then she combined those measurements with local weather stations to provide the crop water balance for the canola.  Using these data, she was able to determine soil water use as indicated by the water content change through the growing season and calculate the depletion of soil water.  

Image of blooming winter Canola

Anecdotally, a dinner plate sized plant can survive winter fairly well.

Megan also took soil samples into the lab from each depth increment at every site and used a chilled mirror hygrometer to construct a moisture release curve.  This helped her to define the apparent permanent wilting point at -1.5 MPa.  She says, “I was able to then see how efficient canola was at extracting available water, and I could look at available water instead of total water contents, which was more useful in terms of plant accessible moisture in the soil profile. It allowed me a consistent platform to compare actual water amounts across sites with differing soil types.  At one site, 12.5% of the water was unavailable, but in the sandier soils at another site, it was 4%.  So there were significant differences in permanent wilting point.”

Water and Physiological Challenges Affect Winter Survival:

Megan found that the June planted canola used every milliliter of available water in the soil profile by late October/early November, but August-planted canola still had some water above wilting left in the profile over the winter, which helped the plants in the spring.  She says, “It was a milder winter, so we didn’t get the usual amount of snow and rain, which probably played a role, but we did not see the profile refilled in the June-planted canola.  In addition, those June plants were purple and wilted by November, so water stress could have hurt the plants in terms of its defenses. However, I think a larger issue was that they grew so large (the crowns actually elongated and bolted so they weren’t close to the soil) they were more susceptible to the harsh temperatures, whereas the August planted canola were much smaller and their crowns stayed right on the soil surface.”  These findings are based on only one year of data, and Megan notes that early plantings have worked well in the milder climate of Pendleton, OR.

What Does it Mean for Farmers?

Megan says, “We were able to surprise a lot of farmers by showing that canola roots access water down to 1.5 to 1.7 m in the fall; it was hard to believe that a winter crop would do that. Also, in my second year’s data, we followed water use all the way through harvest, so we were able to show how much yield we gained for every millimeter of water used, and farmers liked hearing that number as well.  I think it’s useful information that incorporates biophysics principles and answers some questions that these new canola producers are interested in.  I have three locations this season that we are currently following to give farmers a further idea of what the water use looks like, when canola uses that water, and from where in the soil profile.  Hopefully, this research will help them manage their rotations and look at the possibility of adopting canola.”

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

Get more information on applied environmental research in our

LinkedInMessengerRedditThreadsCopy

Apr 25

The Tensiometer: Micro-sized

A strand of a spider’s web is 5 micrometers in width. Microelectromechanical systems (MEMS) devices range in size from 20 micrometers to one millimeter. That’s the incredibly small size of the components used in the tensiometer being developed by PhD candidate, Michael Santiago, and his collaborators, professors Abraham Stroock and Alan Lakso  at Cornell University.

Spider wed with dew water on the strands

MEMS devices can be as small in width as 4 strands of a spider’s web.

The engineer/research team is using MEMS technology to develop a miniature tensiometer (microtensiometer) that has a 100 times larger range than existing tensiometers, is stable for months, communicates digitally, and can be embedded into plant stems to directly measure plant water potential.

Existing Tensiometer Limitations:

Water potential is the best measure of a plant’s hydration relative to growth and product yield. Unfortunately, directly measuring water potential in plant tissue is only possible through labor-intensive, destructive methods such as the leaf pressure bomb and stem psychrometer. A common alternative is to use ‘set-and-forget’ soil tensiometers to measure soil water potential as a proxy for plant water potential, but this method is unreliable for plants with high hydraulic resistance (vines and woody species), where plant water potential is often much less than the water potential in soil. Although soil tensiometers are very accurate and simple to use, they can be large and bulky, and cavitate as soils dry.

A 25 cent coin next to a prototype microtensiometer

Prototype microtensiometer made with MEMS components.

Solution:

The Cornell University research team wants to improve the design of the tensiometer so it can be used in the field for applications such as continuously monitoring and controlling plant water potential in vineyards to consistently produce high-quality wine grapes with an exact flavor/aroma profile.  Santiago says, “We’ve basically miniaturized a tensiometer using microchip technology to the point where it’s this tiny chip inside a wafer. Because of the way we fabricated it, we are hoping to make it an embeddable tensiometer that can go in anywhere and measure tension down to about -100 bars (-10 MPa).”

Developing and Calibrating

Santiago is using a chilled mirror hygrometer to produce solutions of specific water potential to test, calibrate, and characterize the microtensiometer.  He comments, “We’ve been testing it in osmotic solutions. We use the water potential meter for calibrating a solution of PEG (polyethylene glycol), and then we measure it with the tensiometer.”

One hurdle the team has to overcome is finding a membrane that keeps small molecules and ions out of the tensiometer pores: these pollute the water inside the tensiometer and cause measurement errors. Santiago explains, “Our solution right now is to test in solutions of large molecules, such as PEG of 1400 molecular weight. The tensiometer pores are about 3-4 nanometers, extremely small, but small molecules, such as sugars and salts, can still get through. It’s not a problem for the short term because we are directly submerging into solutions of just water and large molecules, but our goal is to go into the environment and insert the tensiometer into soils and plant stems where small molecules are ubiquitous, so we’ll have to find a membrane that works and can handle field testing.”

The team has been experimenting with materials such as Gore-Tex and reverse osmosis membranes [M5]  [M6] hoping to find a membrane that allows water through and keeps ions out, but does not slow the measurement.

Close up of a plant

Researchers want be able to insert the device directly into plant xylem.

What’s Next?

Santiago says the calibrations have worked well. Now the challenge will be putting the tensiometer into different environments such as soil, concrete, and plants. For example, they want be able to insert the device directly into plant xylem, which will require a seal so water is not exiting the system.  And that’s not the only complication. Santiago explains, “We are getting ready to do some testing in soils. The challenge will be getting good data because soil can be really heterogeneous, and we have this sensor with a much larger range than the usual tensiometer. So what do we compare it with? That’s going to be a bit of a challenge.” Santiago says the next few months will be spent getting into some different materials and obtaining some initial publishable data.

Take our Soil Moisture Master Class

Six short videos teach you everything you need to know about soil water content and soil water potential—and why you should measure them together.  Plus, master the basics of soil hydraulic conductivity.

Watch it now—>

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

LinkedInMessengerRedditThreadsCopy
« Older Entries
Newer Entries »