Soil carbon flux research!

21/11/2018
Measuring soil carbon flux gives an insight into the health of forest ecosystems and provides feedback on the effects of global warming. This article, from Edinburgh Instruments, outlines how soil CO2 efflux is determined and the applications of soil carbon flux research.

Soil is an important part of the Earth’s carbon cycle.
Pic: pixabay.com/Picography

The Earth’s carbon cycle maintains a steady balance of carbon in the atmosphere that supports plant and animal life. In recent years, concerns about the increasing levels of CO2 in the atmosphere, indicating a problem in Earth’s carbon cycle, has been a prominent global issue.1,2

As a part of a stable carbon cycle, carbon is exchanged between carbon pools including the atmosphere, the ocean, the land and living things in a process known as carbon flux. Carbon exchange typically takes place as a result of a variety of natural processes including respiration, photosynthesis, and decomposition.

Since the industrial age, humans have begun to contribute to carbon exchange with activities such as fuel burning, and chemical processes, which are believed to be responsible for increasing atmospheric CO2 concentrations and increasing global temperatures.1-3

Soil carbon flux provides feedback on environmental conditions
Soil is a vital aspect of the Earth’s carbon cycle, containing almost three times more carbon than the Earth’s atmosphere. Carbon is present in soil as ‘solid organic carbon’ including decomposing plant and animal matter. Over time, microbial decomposition of the organic components of soil releases carbon into the atmosphere as CO2.4,5

The amount of carbon present in soil affects soil fertility, plant growth, microbial activity, and water quality. Studying the carbon flux of soil gives an insight into an ecosystem as a whole and specific information about microbial activity and plant growth.4-6

Soil carbon flux can also help us to understand and predict the effects of global warming. As global temperatures increase, is it expected that microbial activity will also increase, resulting in faster plant decomposition and increased CO2 efflux into the atmosphere.5,6

Measuring soil CO2 efflux
Determining soil-surface CO2 efflux can be challenging. Researchers commonly employ a chamber combined with CO2 concentration measurements to determine CO2 efflux. A variety of chambers have been designed for such research, some of which are commercially available.7-10

Closed-chamber systems typically pump air through a gas analyzer, which measures CO2 concentration, before returning the air to the chamber. Soil CO2 efflux is then estimated from the rate of increase of CO2 concentration in the chamber.

Open-chambers pump ambient air into the chamber and measure the change in CO2concentration between the air entering the chamber and the air leaving the chamber to determine the soil CO2 efflux.

Of the two chamber types, open chambers are considered more accurate. Closed chambers tend to underestimate CO2 efflux as increased CO2 concentrations in the chamber cause less CO2 to diffuse out of the soil while the chamber is in place.10,11.

Often, CO2 concentrations in chambers are measured periodically and then extrapolated to give an estimation of CO2 efflux. This method can be inaccurate because CO2 efflux can vary significantly between measurements with changes in environmental conditions.

A further limitation of using chambers for CO2 efflux measurements is that chambers typically only provide measurements in one location, while CO2 efflux has been found to vary widely even in relatively homogeneous environments. The overall result is CO2 efflux data with limited temporal and spatial resolution, that does not reflect the environmental situation as a whole.10,12,13

Naishen Liang

A group of researchers from the National Institute for Environmental Studies (Japan) led by Naishen Liang has designed an automated, multi-chamber chamber system for measuring soil-surface CO2 efflux.

As CO2 concentrations are measured automatically using an infrared gas sensor, COefflux can be determined accurately throughout the experiment. The improved temporal resolution, combined with increased spatial detail resulting from the use of multiple chambers gives a better overview of how CO2 efflux varies with time, location, and environmental conditions within an ecosystem.10

Liang and his team have applied his method to gather information about a range of forest ecosystems. Their automated chambers have been used in a variety of forest locations combined with heat lamps to provide high-resolution, long-term data about the effects of warming on microbial activity and CO2 efflux.

Liang’s research has shown that soil temperatures have a significant effect on COefflux in a wide range of forest environments, information that is vital for understanding how global warming will affect forest ecosystems and the Earth’s carbon cycle as a whole.14-17

All chamber systems for determining CO2 efflux rely on accurate CO2 concentration analysis. Infrared gas analyzers are the most widely used method of instrumentation for determining CO2 concentrations in soil CO2 efflux measurement chambers.8,10,18

Infrared gas sensors, such as gascard sensors from Edinburgh Sensors, are well suited to providing CO2 concentration measurements in soil chambers, and are the sensors of choice used by Liang and his team.

The gascard sensors are robust, low-maintenance, and easy to use compared with other sensors. They provide rapid easy-to-interpret results and can be supplied as either complete boxed sensors (the Boxed Gascard) or as individual sensors (the Gascard NG) for easy integration into automated chambers.19,20


Notes, References and further reading
1. ‘The Carbon Cycle’
2. ‘Global Carbon Cycle and Climate Change’ — Kondratyev KY, Krapivin VF, Varotsos CA, Springer Science & Business Media, 2003.
3. ‘Land Use and the Carbon Cycle: Advances in Integrated Science, Management, and Policy’ — Brown DG, Robinson DT, French NHF, Reed BC, Cambridge University Press, 2013.
4. ‘Soil organic matter and soil function – Review of the literature and underlying data’ — Murphy BW, Department of Environment and Energy, 2014
5. ‘The whole-soil carbon flux in response to warming’ — Hicks Pries CE, Castanha C, Porras RC, Torn MS, Science, 2017.
6. ‘Temperature-associated increases in the global soil respiration record’ — Bond-Lamberty B, Thomson A, Nature, 2010.
7. ‘Measuring Emissions from Soil and Water’ — Matson PA, Harriss RC, Blackwell Scientific Publications, 1995.
8. ‘Minimize artifacts and biases in chamber-based measurements of soil respiration’ — Davidson EA, Savage K, Verchot LV, Navarro R, Agricultural and Forest Meteorology, 2002.
9. ‘Methods of Soil Analysis: Part 1. Physical Methods, 3rd Edition’ — Dane JH, Topp GC, Soil Science Society of America, 2002.
10. ‘A multichannel automated chamber system for continuous measurement of forest soil CO2 efflux’ — Liang N, Inoue G, Fujinuma Y, Tree Physiology, 2003.
11. ‘A comparion of six methods for measuring soil-surface carbon dioxide fluxes’ — Norman JM, Kucharik CJ, Gower ST, Baldocchi DD, Grill PM, Rayment M, Savage K, Striegl RG, Journal of Geophysical Research, 1997.
12. ‘An automated chamber system for measuring soil respiration’ — McGinn SM, Akinremi OO, McLean HDJ, Ellert B, Canadian Journal of Soil Science, 1998.
13. ‘Temporal and spatial variation of soil CO2 efflux in a Canadian boreal forest’ — Rayment MB, Jarvis PG, Soil Biology & Biochemistry, 2000.
14. ‘High-resolution data on the impact of warming on soil CO2 efflux from an Asian monsoon forest’ — Liang N, Teramoto M, Takagi M, Zeng J, Scientific Data, 2017.
15. ‘Long‐Term Stimulatory Warming Effect on Soil Heterotrophic Respiration in a Cool‐Temperate Broad‐Leaved Deciduous Forest in Northern Japan’ —Teramoto M, Liang N, Ishida S, Zeng J, Journal of Geophysical Research: Biogeoscience, 2018.
16. ‘Sustained large stimulation of soil heterotrophic respiration rate and its temperature sensitivity by soil warming in a cool-temperate forested peatland’ — Aguilos M, Takagi K, Liang N, Watanabe Y, Teramoto M, Goto S, Takahashi Y, Mukai H, Sasa K, Tellus Series B : Chemical and Physical Meteorology, 2013.
17. ‘Liang Automatic Chamber (LAC) Network
18. ‘Interpreting, measuring, and modeling soil respiration’ — Ryan MG, Law BE, Biogeochemistry, 2005.
19. ‘Boxed Gascard’
20. ‘Gascard NG’

@edinsensors #Environment #NIESJp

Methane detection in mines.

21/03/2018

Mining is big business, with the world’s 50 largest mining companies worth a total of 1 trillion dollars (€0.81 trillion). Worldwide, the mining industry is responsible for the direct employment of 3.7 million people, with over 150 million indirectly supported by small-scale mining operations.  Many other sectors, such as high-tech industry, are also entirely dependent on mined supplies of materials.

Guardian NG detects methane

There is inherent danger in creating and operating within subterranean tunnels which results in a high mining date rate, over 5 deaths per day due to mining accidents recorded in China alone. This is a worldwide problem, with high-profile incidents in the last 10 years occurring in New Zealand, Russia and the US among others.

The most common source of mining accidents, particularly in coals mines, is an explosion of methane gas. Methane is a colourless, odourless gas which is trapped in mines as part of the coal formation process. As coal is formed from compressed plant matter methane is produced as a by-product then, when rocks are excavated, methane is released into the local atmosphere with potential deadly consequences.

Methane Explosions in Mines
Methane explosions in mines are the result of the concentration of a methane leak in a closed environment. If methane reaches a critical concentration in the air, which is between 5 to 15 % it can react with the oxygen to form carbon dioxide, water and heat. This reaction needs a source of ignition to begin. This doesn’t necessarily have to be an open flame, sparks from mining processes, or a high localised temperature (over 600 °C) on hot equipment, can be enough to cause an explosion.

The pressure wave created by a methane explosion is often more dangerous than the initial explosion. The waves can displace large amounts of coal dust, spreading highly flammable particles throughout the air. The dust can ignite as part of a chain reaction, spreading flames along the mining shaft, consuming any available oxygen to further fuel the fire and generating large amounts of toxic gases.

Safety Measures to Avoid Methane Explosions
Methane release is unavoidable in coal mines as it is always present. The problem with methane explosions is not just restricted to active mining sites either. Many abandoned also leak methane gas, potentially into residential areas where it can still reach high enough concentrations to be at risk of explosion.

The risk of methane gas accumulation in mines means that gas sensing is an essential part of any mining safety network. To reduce the risk of methane build up, ventilation equipment is used in mines to keep methane concentrations below the explosion limit.

Sensors can be placed at ventilation exits to mine, measuring the outgassing of methane to determine that the methane concentration in the mine itself is not close to critical methods. External sensors are also important to monitor the release of methane to the environment surrounding the mine.

In order for gas sensing to be an effective safety measure, the gas sensors used must be able to detect low methane concentrations at a high reliability.

The Guardian NG for Methane Detection
One sensor range that is suited to the critical safety issue of detecting methane outgassed from mines is the Guardian NG series from Edinburgh Sensors. Capable of detecting methane concentrations between 0-1%, these infra-red based sensors are sensitive enough to detect even the smallest of leaks.

The Guardian NG series is designed as an easy-to-use, standalone gas sensor that can continually monitor and log methane concentrations in conditions where the gas is present between 0 – 100 % volume, with the most sensitive sensor being able to detect between 0-1%. The sensor has an impressively rapid 1.5 minute warm-up time and is capable of operating in a range of conditions varying from 0 – 95 % relative humidity and 0 – 45 °C.

What makes the Guardian NG series particularly well-suited to mining applications is they can be easily integrated in to existing ventilation equipment. As the sensor itself is electronic and could generate sparks, it should be situated on the surface of the mine measuring gas concentrations released from the mine vents. This provides a guarantee that ventilation systems are working and can also be used to monitoring the off-gassing of old mining sites.

Infra-red sensors offer some advantages over the traditional heat of combustion sensors that are typically used for mining applications and are commonly used in other areas where methane detection is required as methane absorbs infra-red light very strongly at characteristic wavelengths. They also offer faster response times and potentially have longer service lives than heat of combustion sensor alternatives.

One huge advantage of IR sensors in safety applications is the fail-safe nature of the technology. If the IR lamp, and therefore the sensor, fails then no signal is received by the detector, which is an equivalent effect to the sensor detecting a high methane concentration. As a result, a full alarm would sound, notifying staff that the sensor has failed and there is a potentially dangerous situation.

With its sensitivity and accuracy for methane detection and short response time of less than 30 seconds from sample injection, the Guardian NG series offers one answer to the critical safety issue of explosion prevention in mining.

 

@Edinst #PAuto

Simulating the Effect of Climate Change on Agriculture.

01/12/2017
Increased atmospheric CO2 levels and climate change are believed to contribute to extreme weather conditions, which is a major concern for many. And beyond extreme events, global warming is also predicted to affect agriculture.1,2

While climate change is expected to affect agriculture and reduce crop yields, the complete effects of climate change on agriculture and the resultant human food supplies are yet to be fully understood.2,3,4

Simulating a Changing Climate
In order to understand how changes in CO2, temperature and water availability caused by climate change have an impact on crop growth and food availability, Researchers often use controlled growth chambers to grow plants in conditions that mimic the predicted atmospheric conditions at the end of the century. These controlled growth chambers enable precise control of temperature, CO2 levels, humidity, water availability, light quality and soil quality, allowing Scientists to study how plant growth changes in response to elevated temperatures, elevated CO2 levels and altered water availability.

However, plant growth / behaviour in the field considerably varies from in growth chambers. Owing to differences in light intensity, light quality, evaporative demand, temperature fluctuations and other abiotic and biotic stress factors, the growth of plants in tiny, controlled growth chambers does not always sufficiently reflect plant growth in the field. Moreover, the less realistic the experimental conditions used during simulation experiments of climate change, the less likely the resultant predictions will reflect reality.4

Several attempts have been made over the past 30 years to more closely stimulate climate change growing scenarios including free air CO2 enrichment, open top chambers, free air temperature increases and temperature gradient tunnels, although all these methods are known to have major disadvantages. For instance, chamber-less CO2 exposure systems do not enable stringent control of gas concentrations, while other systems suffer from “chamber effects” such as changes in humidity, wind velocity, temperature, soil quality and light quality.4,5

Spanish Researchers have recently reported temperature gradient greenhouses and growth chamber greenhouses, which are specifically designed to remove some of the disadvantages of simulating the effects of climate change on crop growth in growth chambers. An article reporting their methodology was featured in Plant Science in 2014, describing how the Researchers used temperature gradient greenhouses and growth chamber greenhouses to simulate climate change conditions and study plant responses.4

Choosing the Right Growth Chamber
Compared to traditional growth chambers, temperature gradient greenhouses and controlled growth chambers offer increased working area, allowing them to work as greenhouses without the necessity for isolation panels while still allowing precise control of various environmental factors such as temperature, CO2 concentration and water availability.

Researchers have used these greenhouses to investigate the potential effects of climate change on the growth of grapevine, alfalfa and lettuce.

CO2 Sensors for Climate Change Research
Researchers investigating the effects of climate change on plant growth using greenhouses or growth chambers will require highly accurate CO2 measurements.

The Spanish Researchers used Edinburgh Sensors Guardian sensor in their greenhouses to provide accurate and reliable CO2measurements. As a customer-focused provider of high-quality gas sensing solutions, Edinburgh Sensors has been delivering gas sensors to the research community since the 1980s.4,6

The Guardian NG from Edinburgh Sensors
The Edinburgh Sensors Guardian NG provides precise CO2 measurements in research greenhouses simulating climate change scenarios. The sensor provides near-analyser quality continuous measurement of CO2 concentrations, operates in temperatures of 0-45 °C and relative humidity of 0-95%, and has a CO2 detection range of 0 to 3000 ppm. These features make Guardian NG suitable for use in greenhouses with conditions meant to simulate climate change scenarios.

In addition, the Guardian NG can be easily installed as a stand-alone product in greenhouses to measure CO2, or in tandem with CO2 controllers as done by the Spanish Researchers in their temperature gradient and growth control greenhouses.4,6

Conclusions
In order to understand the potential effects of climate change on plant growth and crop yields, it is important to simulate climate change scenarios in elevated CO2 concentrations. For such studies, accurate CO2 concentration measurements are very important.

References

@Edinst #agriculture

Simulating agricultural climate change scenarios.

19/09/2017
Extreme weather, believed to result from climate change and increased atmospheric CO2 levels, is a concern for many. And beyond extreme events, global warming is also expected to impact agriculture.(Charlotte Observer, 7 Sept 2017)

Although it is expected that climate change will significantly affect agriculture and cause decreases in crop yields, the full effects of climate change on agriculture and human food supplies are not yet understood. (1, 2 & 3 below)

Simulating a Changing Climate
To fully understand the effects that changes in temperature, CO2, and water availability caused by climate change may have on crop growth and food availability, scientists often employ controlled growth chambers to grow plants in conditions that simulate the expected atmospheric conditions at the end of the century. Growth chambers enable precise control of CO2 levels, temperature, water availability, humidity, soil quality and light quality, enabling researchers to study how plant growth changes in elevated CO2 levels, elevated temperatures, and altered water availability.

However, plant behavior in the field often differs significantly from in growth chambers. Due to differences in light quality, light intensity, temperature fluctuations, evaporative demand, and other biotic and abiotic stress factors, the growth of plants in small, controlled growth chambers doesn’t always adequately reflect plant growth in the field and the less realistic the experimental conditions used during climate change simulation experiments, the less likely the resultant predictions will reflect reality.3

Over the past 30 years, there have been several attempts to more closely simulate climate change growing scenarios including open top chambers, free air CO2 enrichment, temperature gradient tunnels and free air temperature increases, though each of these methods has significant drawbacks.

For example, chamber-less CO2 exposure systems do not allow rigorous control of gas concentrations, while other systems suffer from “chamber effects” included changes in wind velocity, humidity, temperature, light quality and soil quality.3,4

Recently, researchers in Spain have reported growth chamber greenhouses and temperature gradient greenhouses, designed to remove some of the disadvantages of simulating the effects of climate change on crop growth in growth chambers. A paper reporting their methodology was published in Plant Science in 2014 and describes how they used growth chamber greenhouses and temperature gradient greenhouses to simulate climate change scenarios and investigate plant responses.3

Choosing the Right Growth Chamber
Growth chamber and temperature gradient greenhouses offer increased working area compared with traditional growth chambers, enabling them to work as greenhouses without the need for isolation panels, while still enabling precise control of CO2 concentration, temperature, water availability, and other environmental factors.

Such greenhouses have been used to study the potential effects of climate change on the growth of lettuce, alfalfa, and grapevine.

CO2 Sensors for Climate Change Research
For researchers to study the effects of climate change on plant growth using growth chambers or greenhouses, highly accurate CO2 measurements are required.

The Spanish team used the Edinburgh Sensors Guardian sensor in their greenhouses to provide precise, reliable CO2 measurements. Edinburg Sensors is a customer-focused provider of high-quality gas sensing solutions that have been providing gas sensors to the research community since the 1980s.3,5

The Guardian NG from Edinburgh Sensors provides accurate CO2 measurements in research greenhouses mimicking climate change scenarios. The Edinburgh Sensors Guardian NG provides near-analyzer quality continuous measurement of CO2 concentrations. The CO2 detection range is 0-3000 ppm, and the sensor can operate in 0-95% relative humidity and temperatures of 0-45 °C, making it ideal for use in greenhouses with conditions intended to mimic climate change scenarios.

Furthermore, the Guardian NG is easy to install as a stand-alone product in greenhouses to measure CO2, or in combination with CO2 controllers as done by the Spanish team in their growth control and temperature gradient greenhouses.4,6 Conclusions Simulating climate change scenarios in with elevated CO2 concentrations is essential for understanding the potential effects of climate change on plant growth and crop yields. Accurate CO2 concentration measurements are essential for such studies, and the Edinburgh Sensors Guardian NG is an excellent option for researchers building research greenhouses for climate change simulation.

References

  1. Walthall CL, Hatfield J, Backlund P, et al. ‘Climate Change and Agriculture in the United States: Effects and Adaptation.’ USDA Technical Bulletin 1935, 2012. Available from: http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1000&context=ge_at_reports
  2. https://www.co2.earth/2100-projections Accessed September 7th, 2017.
  3. Morales F, Pascual I, Sánchez-Díaz M, Aguirreolea J, Irigoyen JJ, Goicoechea N Antolín MC, Oyarzun M, Urdiain A, ‘Methodological advances: Using greenhouses to simulate climate change scenarios’ Plant Science 226:30-40, 2014.
  4. Aguirreolea J, Irigoyen JJ, Perez P, Martinez-Carrasco R, Sánchez-Díaz M, ‘The use of temperature gradient tunnels for studying the combined effect of CO2, temperature and water availability in N2 fixing alfalfa plants’ Annals of Applied Biology, 146:51-60, 2005.
  5. https://edinburghsensors.com/products/gas-monitors/guardian-ng/ Accessed September 7th, 2017.
@Edinst #PAuto #Food

Measuring CO2 to optimise bulk storage of food.

24/07/2017

Meeting the food requirements of a growing global population is becoming increasingly difficult. Despite the need for additional food, it is estimated that 50-60% of grain is lost after harvesting, at a cost of about $1 trillion per year. (See note 1 below)

One of the major reasons for lost grain is spoilage due to mould or insect infestation during storage.2 To provide a constant supply of grain year-round, after grains are harvested they are often kept in long term storage. Maintaining the quality of stored grain is crucial, both to ensure the quality of the final food products, and to prevent economic losses for farmers.

Edinburgh Sensors GascardNG Sensor

Insects and moulds can grow in stored grain, and their ability to flourish depends on the temperature and moisture of the stored grain. Moulds are the most common cause of grain spoilage and can cause changes in the appearance and quality of stored grains. Some moulds can release toxic chemicals called mycotoxins which can suppress the immune system, reduce nutrient absorption, cause cancer, and even be lethal in high doses. It is therefore crucially important to prevent the presence of mycotoxins in food products.2

Monitoring Stored Grain
Farmers are advised to check their stored grain weekly for signs of spoilage.3 Traditionally, grains are checked visually and by odour. Grain sampling can allow earlier detection of insects and moulds, but these methods can be tedious and time-consuming. Rapid, simple methods are needed for early detection of spoilage and to prevent grain losses.2

When moulds and insects grow, and respire, they produce CO2, moisture and heat. Temperature sensors detect increases in temperature caused by mould growth or insect infestation, therefore indicating the presence of grain spoilage. However, they are not able to detect temperature increases caused by infestation unless the infestation is within a few meters of the sensors. CO2 sensors can detect the CO2 produced by moulds and insects during respiration. As the CO2 gas moves with air currents, CO2 sensors can detect infestations that are located further away from the sensor than temperature sensors. CO2 measurements are therefore an important part of the toolkit needed to monitor stored grain quality.2

Using CO2 Measurements to Detect Spoilage
CO2 monitoring can be used for early detection of spoilage in stored grains, and to monitor the quality of stored grains. Safe grain storage usually results in CO2 concentrations below 600 ppm, while concentrations of 600-1500 ppm indicate the onset of mould growth. CO2 concentrations above 1500 ppm indicate severe infestations and could represent the presence of mycotoxins.4

CO2 measurements can be taken easily, quickly and can detect infestations 3-5 weeks earlier than temperature monitoring. Once spoilage is detected, the manager of the storage facility can address the problem by aerating, turning, or selling the grain. Furthermore, CO2 measurements can aid in deciding which storage structure should be unloaded first.2

Research published by Purdue University and Kansas State University have confirmed that high CO2 levels detected by stationary and portable devices are associated with high levels of spoilage and the presence of mycotoxins.4,5 Furthermore, they compared the ability of temperature sensors and CO2 sensors in a storage unit filled with grain to detect the presence of a simulated ‘hot spot’ created using a water drip to encourage mould growth.

The CO2 concentration in the headspace of the storage unit showed a strong correlation with the temperature at the core of the hot spot, and the CO2 sensors were, therefore, able to detect biological activity. The temperature sensors were not able to detect the mould growth, despite being placed within 0.3-1 m of the hotspot.6

To enable efficient monitoring of grain spoilage accurate, reliable and simple to use CO2 detectors are required. Gascard NG Gas Detector from Edinburgh Sensors provide accurate CO2 measurements along with atmospheric data, enabling grain storage managers to make decisions with confidence.

The Gascard NG Gas Detector uses a proprietary dual wavelength infrared sensor to enable the long term, reliable measurement of CO2 over a wide range of concentrations and in temperatures ranging from 0-45 °C. Measurements are unaffected by humidity (0-95% relative humidity) and the onboard pressure and temperature sensors provide real-time environmental compensation, resulting in the most accurate CO2 concentration readings.

Conclusion
Easy, fast, and accurate CO2 concentration monitoring during grain storage can provide early detection of grain spoilage, resulting in reduced grain losses, higher quality stored grain, and lower mycotoxin levels. CO2 monitoring could save millions of dollars annually in the grain production industry.4


References

  1. Kumar D, Kalita P, Reducing Postharvest Losses during Storage of Grain Crops to Strengthen Food Security in Developing Countries. Foods 6(1):8, 2017.
  2. http://www.world-grain.com/Departments/Grain-Operations/2016/7/Monitoring-CO2-in-stored-grain.aspx?cck=1 Accessed May 25th, 2017.
  3. HGCA Grain storage guide for cereals and oilseeds, third edition, available from: https://cereals.ahdb.org.uk/media/490264/g52-grain-storage-guide-3rd-edition.pdf Accessed May 25th, 2017.
  4. Maier DE, Channaiah LH, Martinez-Kawas, A, Lawrence JS, Chaves EV, Coradi PC, Fromme GA, Monitoring carbon dioxide concentration for early detection of spoilage in stored grain. Proceedings of the 10th International Working Conference on Stored Product Protection, 425, 2010.
  5. Maier DE, Hulasare R, Qian B, Armstrong P, Monitoring carbon dioxide levels for early detection of spoilage and pests in stored grain. Proceedings of the 9th International Working Conference on Stored Product Protection PS10-6160, 2006.
  6. Ileleji KE, Maier DE, Bhat C, Woloshuk CP, Detection of a Developing Hot Spot in Stored Corn with a CO2 Sensor. Applied Engineering in Agriculture 22(2):275-289, 2006.