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Posts from the ‘Soils’ Category

Oct 31

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Mesh Wireless Sensor Networks: Will Their Potential Ever Be Realized?

Although the idea of mesh wireless sensor networks is not new, the realization of their many benefits have gone largely unrealized. The low success rate of most wireless systems makes the accomplishments of this Johns Hopkins group unique.

Image of bright orange, yellow, and red colored trees in autumn

Soil moisture and temperature are major drivers of seasonal dynamics, soil respiration, carbon cycling, biogeochemical functions, and even the types of species living in a certain area.

The ability to measure soil moisture and temperature is vital to ecologists who work in heterogeneous environments because these parameters are major drivers of seasonal dynamics, soil respiration, carbon cycling, biogeochemical functions, and even the types of species living in a certain area.  But ecologists’ scientific understanding of environmental conditions is hindered when soil moisture measurements disturb the research site, or when field measurements are not collected at biologically significant spatial or temporal granularities. Soil ecologist Dr. Kathy Szlavecz and her husband and computer scientist, Dr. Alex Szalay, both at Johns Hopkins University, are working to solve this dilemma by testing a wireless sensor network (WSN; Mesh Sensor Network), developed by Dr. Szalay, his colleague, computer scientist Dr. Andreas Terzis, and their graduate students. These generate thousands of measurements monthly from wireless sensors. The husband/wife team says that WSN’s have the potential to revolutionize soil ecology by generating a previously impossible spatial resolution.

Diagram of a mesh network data system for soil moisture

Architecture of an end-to-end mesh network data collection system. (Image: lifeunderyourfeet.org)

What is a Mesh Network?

In a mesh wireless sensor network, specially designed radio units (nodes) use proprietary or open communications protocols to self-organize and can pass measurement information back to central units called gateways. Different from star networks where each node communicates directly to the gateway, mesh networks pass data to each other, acting as repeater for other nodes when necessary.

Image of 37 sampling locations at the Smithsonian Environmental Research Center

These are the 37 sampling locations at the Smithsonian Environmental Research Center (SERC) in Edgewater, MD. Data from this deployment is aimed at understanding the effect of forest age, leaf litter input, and earthworm abundance on soil carbon cycling. (Image: lifeunderyourfeet.org)

With low power and reliability as their goal, they are deployed in dense networks to automatically measure conditions such as temperature and soil moisture. These node measurements are taken every few hours over several months. The data are then uploaded onto computers, where it can be maintained and searched. Kathy explains “Without an autonomous sensor system, experiments in need of accurate information about a multitude of environmental parameters on various spatial and temporal scales require a superhuman effort. The inexpensive nature of these sensors enable scientists to place a high-resolution grid of sensors in the field, and get frequent readouts.  This provides an extremely rich data set about the correlations and subtle differences among many parameters, allowing ecologists to design experiments that study not only the gross effects of environmental variables, but also the subtle relations between gradients and small temporal changes.”

Sunlight shining through trees in a forest

Without an autonomous sensor system, experiments in need of accurate information about a multitude of environmental parameters on various spatial and temporal scales require a superhuman effort.

Landscape Studies Benefit from Mesh Networks

Kathy and Alex have deployed mesh wireless sensor networks at several study areas around the state of Maryland.  Kathy says, “Once we record the measurements, we can combine that information with observations of soil organisms to better understand how soil organisms and the soil environment interact. This means we can make better predictions about how human activities will affect the soil environment.” In one urban landscape study, Kathy and her team deployed over 100 nodes around a CO2 flux tower looking at the two major landscape covers in an urban environment: grass and forest.  She explains, “We collected data from nodes connected to soil moisture and temperature sensors for over two years at these sites, and the system worked quite well. We collected about 180 million data points, and that’s no small feat.”

Next week: Learn the results of this research group’s mesh network testing and what Kathy thinks the future holds for this technology.

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Oct 24

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Unraveling the Effects of Dams in Costa Rica (Part 2)

Dr. Rafael Muñoz-Carpena, Professor and University of Florida Water Institute Faculty Fellow and his research team are performing environmental studies on the Palo Verde National Park wetlands, trying to unravel the effects of the dams and how to revert some of the damage (see part one).  This week, find out how the researchers established connectivity in such a remote area,  some of the problems associated with the research, and how the team has addressed some unusual research issues.

ATMOS 41 Weather Station in Palo Verde National Park Wetlands

Surface water elevation gauge station at the Bebedero river. Photo credit: Marco Pazmino Antonio

The Data Challenges of Remote Locations

The team began collecting data, as part of a joint effort with the Organization of Tropical Studies (OTS) research station. However, typical sensors require constant supervision and frequent visits, which imposed a burden on the station staff. There was also the risk of losing data if a sensor malfunction went undetected between monthly visits.  Rafael says, “Sometimes access was not possible due to floods or scheduling issues, so there was a high risk of losing information. To fix the problem (thanks to a National Science Foundation grant awarded to OTS) we integrated the sensors into a system that gives us remote access on a daily basis. This allows us to see the status of the instrumentation in near real-time, and thus coordinate with OTS to replace sensors if needed.”

Fauna in Palo Verde

Glimpse of the fauna in Palo Verde. Photo credit: Alice Alonso

Connectivity Issues

The team had a difficult time finding internet connectivity because the area is so remote. After trying several solutions, they finally built their own cell towers. The stations are now outfitted with cellular-enabled data loggers in conjunction with rain gauges and soil moisture and salinity sensors. The stations also include a standing well to measure surface and river water levels and monitor flooding stages. These are coupled with shallow water table wells, installed below the surface at 3-5 meters.  Rafael says, “These are tidal rivers, so we get a lot of activity up and down. We look at river data in conjunction with inland responses to try and get an idea of the influence of the river on the shallow groundwater nearby. All these data feed into a database that researchers and stakeholders can look at.”

Composite image contrasting the Palo Verde wetland in the 1986 and the wetland in recent days (2012) during the wet seasons. It highlights the encroachment of vegetation and Typha domingensis (cattail), closing the patches of open water and reducing biodiversity and sites for birds feeding and nesting.

Composite image contrasting the Palo Verde wetland in the 1986 and the wetland in recent days (2012) during the wet seasons. It highlights the encroachment of vegetation and Typha domingensis (cattail), closing the patches of open water and reducing biodiversity and sites for birds feeding and nesting.

Internal Drivers

Dr. Muñoz-Carpena says because of the lag in the environmental response, it is not immediately clear to the general public that the wetland behavior is the result of what is happening upstream. People fail to see a connection. Therefore unraveling the data in a way that is clear is the first challenge of the project. He adds, “There are also internal drivers such as park management changes that compound the effects of the dams. Originally park managers tried invasive plant control with fire and cattle. Now they control the invasive with blade-rigged tractors that mow the cattail. But this is a highly expensive and temporary measure with recurrent costs, which provides no definitive solution to the cattail invasion. It’s important to understand the changes are not just the result of what’s happening locally. We need to find permanent solutions by tracking down the root of the problem.”

Endangered Jabiru birds in the trees in Palo Verde National Park

Endangered Jabiru in the Palo Verde National Park. Photo credit: Alice Alonso

Plants are Not the Only Invasives

Cattails are not the only invaders that plague the wetlands. Rafael explains, “The other problem is that there is trafficking going on in the park. The men see these data logger boxes with silver antennas, and they think it’s a camera, so they break off the antennas. We are now putting up signs that say, ‘This is not the government watching you. This is research to protect your environment,’ but we are afraid the next time they will break the boxes and everything that goes with them. We won’t have the manpower or the financial resources to go down there and fix the data loggers for another six months.”

Image of a typical monitoring station set up in a more dry area

Example of a typical monitoring station: Surface and subsurface water elevation and EC monitoring wells, and soil moisture and EC at 30 and 60 cm depths. Sensors connected to a wireless cellular data logger for near-real-time data access. Photo taken during the dry season. Photo credit: Alice Alonso

What’s Next?

Over the last three years the team has collected a high-resolution database of fifteen to thirty minute timed steps, with over 100 sensors deployed in twelve spatially-distributed monitoring stations around the park. With that data, Rafael’s team is conducting exploratory types of analysis to study not only potential drivers of change, but also the cause of the drivers. They want to understand potential initiatives they could introduce to make the system more sustainable. Rafael says, “Once we develop integrated hydrological models and test them for the conditions in Costa Rica, hopefully we can understand the behavior in the past and forecast some different scenarios for the future.” Because many regions in the world suffer the impacts of interbasin water transfer, this research can inform future research policy at a broader scale.

Monkeys hang from a tree branch in Palo Verde National park

Glimpse of the fauna in Palo Verde. Photo credit: Alice Alonso

See a map of the instrumentation network within the Palo Verde National Park.

Conceptual representation of the Palo Verde National Park in the context of the Tempisque watershed system.

Conceptual representation of the Palo Verde National Park in the context of the Tempisque watershed system.

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Oct 17

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Unraveling the Effects of Dams in Costa Rica

Thirty years ago, in Costa Rica’s Palo Verde National Park, the wetlands flooded regularly and eco-tourists could view thousands of waterfowl. Today, invasive cattail plants cover portions of the wetland which has subsequently dried up and become colonized by hardwoods. Consequently, the number of birds has fallen dramatically.

Flocks of birds flying against a sunset

The number of birds on Palo Verde National Park has fallen dramatically. (Image: anywherecostarica.com)

Some people blame the dams built in the 1970s which introduced hydrological power and created a large irrigation district in the remote region. Dr. Rafael Muñoz-Carpena, Professor and University of Florida Water Institute Faculty Fellow and his research team are performing environmental studies on the wetlands, trying to unravel the effects of the dams and how to revert some of the damage. Rafael explains, “We have a situation where modern engineering brought about social improvements, helpful renewable resources, and irrigation for abundant food production. But the resulting environmental degradation threatens a natural region in a country that depends on eco-tourism.”

Birds in a river at Palo Verde National Park

“A vast network of mangrove-rich swamp, lagoons, marshes, grassland, limestone outcrops, and forests comprise the 32,266 acre Palo Verde National Park.” (Image and text: anywherecostarica.com)

Are The Dams Responsible?

Dr. Muñoz-Carpena says because of lack of historical data it’s difficult to untangle and separate all the factors that have caused the environmental degradation. He adds, “Thirty years ago Palo Verde National Park was part of a large wetland system which was important to all of Central America because it contained many endangered species and was a wintering ground for migratory birds from North America. The Palo Verde field station on the edge of the wetland, operated by the Organization of Tropical Studies (OTS), attracted birdwatchers and wetland scientists from all over the world.”

In the 1970’s, with international funding, a dam was built in the mountains to collect water from the humid side of Costa Rica in order to generate hydroelectric power. It was clean, abundant, and strategically important.  With the water transferred to the dry side of the country, a large irrigation district was created to not only produce important crops to the region like rice and beans, but to distribute the land among small parcel settlers.

Flock of birds in the grasslands at Palo Verde National Park

“Birding is the principal draw of visitors to the park.” (Image and text: anywherecostarica.com)

Over the years, however, the wetland area slowly degraded to the point where its Ramsar Convention wetland classification is under question. Rafael says that understanding the causes of the degradation, the impacts of the human system, and how the natural and human systems are linked, is the big question of his research, and there are many factors to consider. “The release of the water, ground and surface water (over)use, agriculture, human development, and a larger population are all factors that could contribute to this degradation. Everything compounds in the downstream coastal wetlands. In collaboration with OTS and other partner organizations and universities, we are trying to disentangle these different drivers.”

Grasslands and swamps with mountains in the background

Understanding the causes of the degradation, the impacts of the human system, and how the natural and human systems are linked, is the big question of this research. (Image: anywherecostarica.com)

A Lack of Historical Data

One of the challenges the researchers face is to gather a sufficient amount of temporal and spatial information about what happened in the past forty years.  There are no public repositories of data to tap, and the information is spotty and hard to access. Rafael says, “Thanks to the collaboration of many local partners, we have been able to gather enough information to stitch together a large database out of a collection of non-systematic studies. The biggest challenge is to harmonize data that has been collected by different people in non-consistent ways.” This large database now contains the best long-term record possible for key hydrologic variables: river flow, groundwater stage, precipitation, and evapotranspiration.

The team is also using remote sensing sources to try to obtain time-series data for land-use and vegetation change, and will have those data ground-truthed through instruments that are collecting similar time-series data. Rafael says, “The idea is to build a network that will allow us to overlap some of the previous data sources with our own, validate and upscale the ground data with remote sensing sources, enabling us to put together a detailed picture of what happened.”

Next Week:  Find out how the researchers established connectivity in such a remote area,  some of the problems associated with the research, and how the team has addressed those issues.

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Oct 10

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Measuring NDVI in a Greenhouse Presents Challenges (Part 2)

University of Georgia researcher, Shuyang Zhen, wanted to find out if she could optimize greenhouse irrigation with reference evapotranspiration calculated from environmental factors and a crop coefficient, using NDVI measurements to adjust for canopy size (see part 1). Learn the results of the experiment and how fast growth and flowering caused problems with the NDVI measurement.

Researchers measuring the NDVI of green plants in a greenhouse

Shuyang’s experimental setup.

Fast Growth Causes Problems

Shuyang says because the plants grew so large, the canopy filled in beyond what the sensor could see.  That meant there was additional leaf area that participated in vapor loss which wasn’t identified by the NDVI sensor.  As the canopies approached moderate-to-high canopy densities, Shuyang observed that the NDVI readings became less responsive to increases in canopy size. To work around this problem, Shuyang tried to calculate a vegetation index called the Wide Dynamic Range Vegetation index with the spectral reflectance outputs of the two wavebands measured by the NDVI sensor. Shuyang says, “This index was supposed to improve the sensitivity at higher canopy density, so I transformed all my data and was surprised that it actually improved the sensitivity when the canopy density was lower.  But at a higher canopy density it wasn’t as effective.”

Researchers measuring NDVI of petunias in a greenhouse

The red flowers reflected a lot of red light compared to the leaves, which confused the NDVI measurement.

Plant flowering also caused problems with the NDVI measurement.   Shuyang explains, “We had one cultivar of petunia with red flowers which formed on top of the canopy. The red flowers reflected a lot of red light compared to the leaves, which confused the NDVI measurement.  The NDVI value gradually decreased when the plants started to flower. There was no way I could get around that issue, so in some of the replicates, I removed the flowers, and in some I kept the flowers so I could compare the different responses and characterize why it happened.”

Poinsettia plant with red small flowers

The NDVI was very sensitive to the increase in crop size when the canopy was relatively small, but when you reach a certain canopy size and the canopy closure was nearly complete, then the sensitivity decreased.

Summary and Future Studies

During the early stages of growth, the research team saw a linear relationship between NDVI and crop coefficient. However, when the crop coefficient reached higher values, the response leveled off.  Shuyang says, “The response failed to change with further increases in the crop coefficient. The NDVI was very sensitive to the increase in crop size when the canopy was relatively small, but when you reach a certain canopy size and the canopy closure was nearly complete, then the sensitivity decreased.”  

Six poinsettia plants with small flowers arranged with one in the middle and five around the middle one in a circle

Lack of NDVI sensitivity during canopy closure and flowering translated to a problem with under-irrigation,

Shuyang adds that the lack of NDVI sensitivity during canopy closure and flowering translated to a problem with under-irrigation, so the team is thinking about developing separate models for different canopy stages.  She explains, “When the canopy reaches high canopy closure we may have to add an additional coefficient to compensate for that underestimation, but it’s difficult to evaluate what kind of coefficient we should use without more data. We need to do more studies to get an idea of what kind of adjustments will make the prediction more precise.”

Learn more about Shuyang’s work on the University of Georgia horticulture blog.

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Sep 5

Can Canopy Measurements Determine Soil Moisture? (Part 2)

Dr. Y. Osroosh, now a researcher at Washington State University, believes that plants are the best soil moisture sensors (see part 1).  He and his team have developed a new model for interpreting plant canopy signals to indirectly determine soil moisture in a Fuji apple orchard.  Below are the results of their efforts and what he sees as the future of this research.

Close up of flower blooming

Could plants be the best indicators of soil moisture?

The Results

Osroosh says they expected to see correlations, but such strong relationships were unexpected. The team found that soil water deficit was highly correlated with thermal-based water stress indices in drip-irrigated apple orchard in the mildly-stressed range. The relationships were time-sensitive, meaning that they were valid only at a specific time of day. The measurements taken between 10:00am and 11:00am (late morning, time of maximum transpiration) were highly correlated with soil water deficit, but the “coefficient of determination” decreased quickly and significantly beyond this time window (about half in just one hour, and reached zero in the afternoon hours).  Osroosh says this is a very important finding because researchers still think midday is the best time to measure canopy water stress index (CWSI). He adds, “The apple trees showed an interesting behavior which was nothing like what we are used to seeing in row crops. They regulate their stomata in a way that transpiration rate is intense late in the morning (maximum) and late in the afternoon. During the hot hours of afternoon, they close their stomata to minimize water loss.”

Picture of a corn field

Researchers have found good relationships between CWSI and soil water content in the root zone near the end of the season at high soil water deficits in row crops.

Other Research

Osroosh points to other efforts which have tried to correlate remotely-sensed satellite-based thermal or NIR measurements to soil water content. He says, “The closest studies to ours have been able to find good relationships between CWSI and soil water content in the root zone near the end of the season at high soil water deficits in row crops. Paul Colaizzi, a research agricultural engineer did his PhD research in part on the relationship between canopy temperature, CWSI, and soil water status in Maricopa, Arizona; also motivated by Jackson et al. (1981). Steve Evett and his team at Bushland, Texas are continuing that research as they try to develop a relationship between CWSI and soil water status that will hold up. They are using a CWSI that is integrated over the daylight hours and have found good relationships between CWSI and soil water content in the root zone near the end of the season when plots irrigated at deficits begin to develop big deficits.”

Picture of a green apple on a tree

Osroosh wants to study other apple cultivars, tree species, and perhaps even row crops, under other irrigation systems and climates.

What’s The Future?

In the future, Osroosh hopes to study the limitations of this approach and to find a better way to monitor a large volume of soil in the root zone in real-time (as reference). He says, “We would like to see how universal these equations can be. Right now, I suspect they are crop and soil-specific, but by how much we don’t know. We want to study other apple cultivars, tree species, and perhaps even row crops, under other irrigation systems and climates. We need to monitor crops for health, as well, to make sure what we are measuring is purely a water stress signal. One of our major goals is to develop a sensor-based setup which, after calibration, can be used for “precise non-contact sensing of soil water content” and “stem water potential” in real-time by measuring canopy temperature and micrometeorological parameters.”

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Aug 29

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Can Canopy Measurements Determine Soil Moisture?

As a young university student, Dr. Y. Osroosh, now a researcher at Washington State University, wanted to design the most accurate soil moisture sensor.  Over the years, however, he began to realize the complexity and difficulty of the task.  Inspired by the work of Jackson et al. (1981) and researchers in Bushland, TX, he now believes that plants are the best soil moisture sensors.  He and his team developed a new model for interpreting plant canopy signals to indirectly determine soil moisture.

Apples on an open air tree

The team measured microclimatic data in an apple orchard.

How Can Plants Indicate Water in Soil?

Osroosh and his team wanted to use plant stress instead of soil sensors to make irrigation decisions in a drip-irrigated Fuji apple tree orchard. But, the current practice of using the crop water stress index (CWSI) for detecting water stress presented some problems, Osroosh comments, “Currently, scientists use either an empirical CWSI or a theoretical one developed using equations from FAO-56, but the basis for FAO-56 equations is alfalfa or grass, which isn’t similar to apple trees.”  One of the main differences between grass and apple trees is that apple tree leaves are highly linked to atmospheric conditions. They control their stomata to avoid water loss.  

Apple tree canopy in an open air field

There is high degree of coupling between apple leaves and the humidity of the surrounding air.

So Osroosh borrowed a leaf porometer to measure the stomatal conductance of apple trees, and he developed his own crop water stress index, based on what he found.  He explains, “We developed a new theoretical crop water stress index specifically for apple trees. It accounts for stomatal regulations in apple trees using a canopy conductance sub-model. It also estimates average actual and potential transpiration rates for the canopy area which is viewed by a thermal infrared sensor (IRT).”

Fuji open air apple orchard (Roza Farm, Prosser, WA).

Fuji apple orchard (Roza Farm, Prosser, WA) where Osroosh performed his research.

What Data Was Used?

Osroosh says they established their new “Apple Tree” CWSI based on the energy budget of a single apple leaf, so “soil heat flux” was not a component in their modeling. He and his team measured soil water deficit using a neutron probe in the top 60 cm of the profile, and they collected canopy surface temperature data using thermal infrared sensors. The team also measured microclimatic data in the orchard.  

Close up of an apple on a tree

Neutron probes were problematic, as they did not allow collection of data in real time.

Osroosh comments, “The accuracy of this approach greatly depends on the accuracy of reference soil moisture measurement methods.  To establish a relationship between CWSI and soil water, we needed to measure soil water content in the root zone precisely. We used a neutron probe, which provides enough precision and volume of influence to meet our requirements.  However, it was a labor and time intensive method which did not allow for real-time measurements, posing a serious limitation.”

Next week: Learn the results of Dr. Osroosh’s experiments, the future of this research, and about other researchers who are trying to achieve similar goals.

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Aug 22

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Do Soil Microbes Influence Plant Response to Heat Waves? (Part II)

Rachel Rubin, PhD candidate at Northern Arizona University and her team at Northern Arizona University are investigating the role soil microbes play in plant response to heat waves, including associated impacts to microbial-available and plant-available water (see part 1). Because heat waves threaten plant productivity, they present a growing challenge for agriculture, rangeland management, and restoration. Below are the results of Rachel’s experiments, some of the challenges the team faced, and the future of this research.

A herd of cows grazing in a pasture

Heat waves present a growing challenge for agriculture, rangeland management, and restoration.

Challenges

Rachel says the experiment was not without its difficulties. After devoting weeks towards custom wiring the electrical array, the team had to splice heat-resistant romex wire leading from the lamps to the dimmer switches, because the wires inside the lamp fixtures kept melting. Also, automation was not possible with this system. She explains, “We were out there multiple times a day, checking the treatment, making sure the lamps were still on, and repairing lamps with our multi-tools. We used an infrared camera and an infrared thermometer in the field, so we could constantly see how the heating footprint was being applied to keep it consistent across all the plots.”

Arizona Fescue plant

Arizona Fescue (image: wickipedia.com)

Some Grass was Heat Resistant

Rachel says her biggest finding was that all of the C4 grasses survived the field heat wave, whereas only a third of the Arizona Fescue plants survived. She adds that the initially strong inoculum effects in the greenhouse diminished after outplanting, with no differences between intact, heat-primed inoculum or sterilized inoculum for either plant species in the field. “It may be related to inoculum fatigue,” she explains, “the microbes in the intact treatment may have become exhausted by the time the plants were placed in the field, or maybe they became replaced, consumed, or outcompeted by other microbes within the field site”. Rachel emphasizes that it’s important to conduct more field experiments on plant-microbe interactions. She says, “Field experiments can be more difficult than greenhouse studies, because less is under our control, but we need to embrace this complexity. In practice, inoculants will have to contend with whatever is already present in the field. It’s an exciting time to be in microbial ecology because we are just starting to address how microbes influence each other in real soil communities.”

Grass going to seed in an open-air field

Diminished effects may be related to inoculum fatigue.

What’s In Store?

Now that the team has collected data from the greenhouse and from the heat wave itself, they have started looking at mycorrhizal colonization of plant roots, as well as sequencing of bacterial and archaeal communities from the greenhouse study. Rachel says, “It’s quite an endeavor to link ‘ruler science’ plant restoration to bacterial communities at the cellular level. I’m curious to see if heat waves simply reduce all taxa equally or if there is a re-sorting of the community, favoring genera or species that are really good at handling harsh conditions.”

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Aug 15

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Do Soil Microbes Influence Plant Response to Heat Waves?

Rachel Rubin, PhD candidate at Northern Arizona University, is interested in the intersection of extreme climate events and disturbance, which together have a much greater impact on plant communities. She and her team at Northern Arizona University are investigating the role soil microbes play in plant response to heat waves, including associated impacts to microbial-available and plant-available water.

Wheat with sun shining through it

Plants have a tight co-evolutionary history with soil microbes. It has been said that there is no microbe-free plant on earth.

Because heat waves threaten plant productivity, they present a growing challenge for agriculture, rangeland management, and restoration.

Can Soil Microbes Increase Heat Resistance?

Many plants maintain mutualistic associations with a diverse microbiome found within the rhizosphere, the region of soil that directly surrounds plant roots. These “plant growth-promoting rhizobacteria” and arbuscular mycorrhizal fungi provision limiting resources including water, phosphorus and nitrogen in exchange for photosynthetically derived sugars. However, we understand very little about whether extreme events can disrupt these interactions.

Tubes of layered dirt

Fig. 1. Fine roots exploring the inoculum that was added as a band between layers of potting mixture.

Rachel and her team exposed rhizosphere communities to heat stress and evaluated the performance of native grasses both in the greenhouse, and transplanted under an artificial heat wave. They hypothesized that locally-sourced inoculum (a sample of local soil containing the right microbes) or even heat-primed inoculum would help alleviate water stress and improve survival of native grasses.

The Experiments

Rubin started in the greenhouse by planting Blue Grama (Bouteloua gracilis, C4 grass) and Arizona Fescue (Festuca arizonica, C3 grass) and assessed their responsiveness to locally collected soil inoculum that had either been left intact, pre-heated or sterilized (Fig. 1). Rubin says, “We expected that our plants would benefit the most from having intact soil microbe communities. But, we were surprised to find very large differences between plant species. Blue Grama performed the best with intact inoculum, whereas Arizona Fescue performed better with pre-heated or sterilized soil”. This could mean that Blue Grama is more dependent on its microbiome, whereas Arizona Fescue engineers a rhizosphere that contains more parasitic microbes rather than mutualistic microbes. Rachel says that understanding this relationship is important for tailoring plant restoration projects to local conditions. Plants that exhibit high levels of mutualisms with their rhizosphere might require an extra inoculum “boost” in order to successfully establish in highly degraded soil, whereas we should not bother to inoculate plants that tend to harbor parasites within their rhizosphere.

Research plot using infrared sensors and METER soil water content and soil water potential sensors

Fig. 2. A heated plot in the foreground connected to infrared lamps, water content and matric potential sensors, and EM50 data loggers.

After the team studied these responses, they planted the grasses into a degraded section of a grassland and installed an array of 1000-Watt ceramic infrared lamps mounted on steel frames (Fig. 2) to address whether inoculation influenced plant performance and survival. With help from a savvy undergraduate electrical engineering major (Rebecca Valencia), Rubin simulated a two-week heat wave while monitoring soil temperature and moisture using water content and water potential sensors.  She also measured plant performance (height, leaf number and chlorophyll content) before, during, and after the event. Control plots had aluminum “dummy lamps” to account for shading.

An infrared photo of the expirement

An infrared photo, which is how Rachel determined that the heating footprint was evenly distributed on all the plants. The scale bar on the right is in degrees C.

Data obtained from soil sensors helped Rachel to measure heating treatment effects as well as rule out a potential cause for plant mortality: soil moisture. “Soil temperature was on average 10 degrees hotter in heated plots than control plots, but matric potential and soil water content were completely unaffected by heating. This tells us that the grasses died from reasons other than water stress– perhaps a top-kill effect.” Although growing concern over heat waves in agriculture is centered around accompanying droughts, this experiment demonstrates that heating can produce negative effects on some species even when water is in plentiful supply.

Next week:  Learn the results of Rachel’s experiments, some of the challenges the team faced, and the future of this research.

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Aug 8

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A New Method for Preventing Snow Mold In Winter Wheat (Part 2)

When faced with a reluctant spring thaw, dryland wheat growers know they have only two weeks to remove the snow from their fields, or large sections of their crop will die off from snow mold.  Melting the snow artificially can be an expensive process, but one southern Idaho wheat grower has found a unique solution that could save both money and the environment  (see part 1).  He covers the snow with displaced topsoil, which speeds up the warming process and is less expensive than using traditional fly ash.  This week, find out which techniques Campbell uses to save time and money while redistributing his soil.

A snow dusted field with a partly cloudy sky and a bright sunset

Campbell says the number of passes he has to make with his tractor makes a difference.

Soil Application

Campbell says the number of passes he has to make with his tractor makes a difference, so he spreads the soil in patches, rather than evenly, in order to save time and money.  “What we’ve found is, if you can get the soil deposited every 40 feet (9 m), you start changing the temperature in the whole area, and not just where the soil was dropped. The breeze will spread the warmth, and the snow in between the patches of soil will melt a lot faster.  We do adjust our spacing depending on the amount of snow. If there’s more snow, that means we’ve got less time, and it’s got to melt faster, so we’ll place the patches of soil closer together for more even coverage.  

Tractor sitting in a field with a researcher standing in front of it

Using a tractor to spread the soil in patches, rather than evenly, saves time and money.

Campbell adds that he is selective on which field he spreads the soil.  If the weather conditions are not looking good, and they have deep snow, then they may skip a field they think they can’t save.  Or if the fields further south have less snow, and the weather looks warm, they may also skip that field because the snow may melt on it’s own.  There are challenges in trying to make those predictions, however.  He says, “It’s hard to make those guesses based on the weather forecast because the predictions just aren’t very accurate a couple of weeks out. One year the forecast was sunny, so we applied fly ash to the fields.  But the next day it snowed a foot, and it was two weeks before that snow melted so the sun could get to the ash.  We lost quite a bit of grain that year.”

Sun shining on a wheat field

Campbell is selective on which field he spreads the soil.

Future Plans

Next year Campbell will try mixing the soil with some fly ash, to take advantage of the ash’s darker color.  He says, “We’re going to keep putting the soil back on the field. It’s less expensive, and we don’t have to haul it. Next year we’ll try mixing the soil with about ⅓ ash so we can get it a little blacker.   It will be a nice middle ground where the dark color will melt the snow, yet it won’t cost too much.  And we can redistribute the eroded, nutrient-rich topsoil.”

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Aug 1

A New Method for Preventing Snow Mold In Winter Wheat

Each year in early spring, dryland wheat farmers battle for their crop’s survival.  As temperatures climb to 0 degrees C, the dark, wet microclimate underneath the snow begins to propagate snow mold.  

Wheat spikes in a green wheat field

Wheat spikes in a wheat field.

Soil scientist, Dr. Colin Campbell says, “Soil under a blanket of snow can warm as spring temperatures rise, despite their icy covering. Temperatures above freezing and the water from snowmelt are a perfect environment for mold to grow.“

When faced with these weather conditions, wheat growers know they have only a couple of weeks to remove the snow, or large sections of their crop will die off. Melting the snow artificially can be an expensive process, but one southern Idaho wheat grower has found a unique solution that could save both money and the environment.

Fresh fluffy snow

Temperatures above freezing and the water from snowmelt are a perfect environment for mold to grow.

The Old Method  

Traditionally, wheat growers have spread fly ash (ash from coal) on the spring snow to try and speed the melting process.  The black fly ash creates a warmer microclimate by absorbing more solar radiation rather than reflecting it.  To demonstrate its effectiveness, the USDA performed studies using fly ash to speed snow melt, with positive results. However, growers say the challenge is using the method in a way that is economical on dryland wheat where the profit margin is narrow.  Bryce Campbell, a dryland wheat farmer near Burley, ID, says, “Some people use fly ash to get in the field faster or to get the water flowing into the soil, but our primary goal is to prevent snow mold from killing the winter wheat.  If that happens, we have to replant the crop to a spring crop which yields a lot less.  Our goal is to try and keep our crop alive.”  

Field with loose top soil and extensive edging

During heavy rain events, topsoil washed down to the edges of the field, collecting in dikes Campbell constructed.

An Inexpensive New Method

Campbell has used fly ash in the past, but last year, he had a better idea.  He noticed that during heavy rain events, some of his topsoil washed down to the edges of the field, collecting in dikes he constructed and eventually becoming dried and powdery. He wondered if he could use that soil as an economical replacement for fly ash. In the fall, he collected some in a truck and left it to dry completely in the back of his shed; then this season, he spread it over the spring snow. Seeing the results, he decided it was worth the effort, both economically and environmentally.  Campbell estimated the fly ash melt to be approximately 30% faster than the powdered soil because of its darker color, but the soil was free, which made a difference in his bottom line.

wheat crop

If snow mold kills the wheat crop, growers have to replant the crop to a spring crop which yields less.

He adds, “Some of the wheat farmers down the road are using a finely ground coal dust product to melt their snow. It’s a great product, and it works really well for melting snow, but their cost is about $20/acre.  When you spread that on a thousand acres, that’s $20,000.  I can put my soil on a thousand acres, and my only cost is two hours of gathering up the soil plus a day and a half in the tractor for application.”

Next week:  Find out which techniques Campbell uses to save time and money redistributing his displaced soil.

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

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