The Carbon Sponge Hub at White Feather Farm has been awarded a 2024 Northeast SARE Farmer Grant to lead a network of five small farms in New York’s Hudson Valley region to continue to trial and evaluate white-grain, annual sorghum for yield and changes in soil health while also evaluating a suite of off- the-shelf field monitoring tools, including the microBIOMETER®.
The five farms are: Coming Home Farm, Foxtrot Farm & Flowers, Nimble Roots Farm, Sweet Freedom Farm and White Feather Farm. Sorghum, originally from East Africa, has great potential as both a human food and climate-smart crop capable of helping sequester carbon in soil. Farmers in regions where sorghum has not been widely grown, like the Hudson Valley, can take advantage of the plant’s ability to adapt to a wide range of conditions and provide ecosystem services on farms — especially increasing soil organic carbon — while also generating revenue.
Alongside field testing, Carbon Sponge will send samples to two professional labs and work with soil scientists to analyze results. The goal is to endorse specific tests and carbon targets for farmers. Carbon Sponge is interested in changing the profile of sorghum in the U.S., including where it is grown, how it is grown and what it is used for. A final report featuring the five farm case studies and recommendations for how to incorporate annual sorghum as a cash crop on a small farm and priorities for future research and investments will be published in 2025.
During the 2024 season, Carbon Sponge will host public workshops and community volunteer days to share research, like during Soil Fest at White Feather Farm on July 27.
We first had the pleasure of working with Briana Alfaro and Soul Fire Farm in 2021 when they began testing soil with farmers in their network as part of their SARE research project, Soil Carbon Capture for Diverse Farmers; Black, Latinx, Asian, Indigenous and other farmers and farm workers of color take the lead in testing soil carbon sequestration strategies and measurement protocols and disseminate those findings to the farming community in both English and Spanish.
Every two years the Soul Fire Farm team takes a closer look at the soil ecosystem and assesses how healthy their soil is. They do this by performing a series of in-field tests. Long before the western study of soil science, Indigenous communities practiced–and still practice–methods of evaluating soil health using characteristics such as color or the presence of specific plants or insects that tell us something about the system as a whole. On their soil testing days, they count the number of earthworms, perform a slake test to observe aggregate stability, look at soil color as an indicator of organic matter, and use the microBIOMETER® field kit to assess soil biology.
You can learn more in their Guide to In-Field Soil Health Measurement Protocols: How Alive is My Soil (English) & ¿Qué tan vivo está mi suelo? (Español), and by watching their Liberation on Land skill share videos: Soil Carbon part 1, Soil Carbon part 2 & Investigating Soil with an Auger.
This article was provided to us by Scott Hortop, a retired volunteer and now student of soil, located in the Ottawa Valley, Ontario, Canada. Scott wants to use his retirement to do one important thing for the climate.
At ONfungi we own two microBIOMETER® soil testing kits which we use to determine the fungal to bacterial ratio (F:B) of the Johnson-Su fungal dominant compost (FDC). The ONfungi group makes FDC from tree leaves.
We are excited by the potential of leaf mold to:
• Reduce agricultural dependence on external inputs• Divert leaf organics from landfills• Replenish the inventory of carbon in the soil by drawing down the carbon in the atmosphere• Grow knowledge about working with mother nature to address climate change
Our first FDC bioreactor batch was started in Spring 2018. Since then, we have put up a total of 15 batches; 8 of them in fall 2021.“It took us 3 batches before we faced the fact that we needed to know whether what we were producing was actually what we hoped it was. Our enthusiasm needed to be grounded. What is the fungal bacteria (F:B) ratio in our FDC?,” says Scott Hortop, wizard of compost for the ONfungi group. “This is why we have found the microBIOMETER® to be our most useful tool.”“Dr. David Johnson’s talks have shown us eloquently how the F:B ratio is the most meaningful indicator for soil health”, Hortop explains. “As we share our fungal dominant compost (FDC) with other users, we owe them a solid measure of what they are getting. When we and others share our FDC experiments with each other at the Chico State University Registry of Johnson-Su Bioreactors, the majority of us have been unable to report F:B ratios. This has now changed. With the microBIOMETER® we can confirm that we have the right ratio of ingredients by taking a real measure of the F:B ratio.”Its All Relative – Isn’t it the change and the direction of changes that we really need to know? Of course, it might be nice to think every microbe was identified and counted under a microscope, but that precision comes at a HUGE cost and most likely doesn’t alter the conclusion. The next thing we need to do to strengthen the microbial community.
Immediacy – When you are checking in on living microbes in soil, some of whom are reproducing and dying in a matter of minutes and others taking years, the best timing for a test is here and now. In a world rich with distraction and delay, its awesome to get a result from your testing efforts immediately.
True Cost Per Data Point – For the purpose of our bioreactors, give it a think: the modest variable costs per test, the modest labour to execute a test which is just minutes beyond the time required for sample collection, the VERY efficient and effective recording of results, and the $0 sample shipping cost.
In an ONfungi citizen science trial last summer by one of our volunteers in White Lake, Ontario, 2 sunflower seeds were planted in late June into moderately degraded farmland (microBIOMETER® F:B 0.7:1; 464 µg C/g).The control seed (left) received no soil amendments. The 2nd seed (right) was planted with 50 grams (a small handful) of Johnson-Su fungal dominant compost (microBIOMETER® F:B 1.7:1; 700 µg C/g) surrounding the seed. For 8 weeks both plants received identical, adequate watering. The 8-week photo below shows the control sunflower on the left suffering from an invasion of cucumber beetles with less than ½ the height and 1/3 the stalk width compared to the sunflower on the right with FDC at its root zone. Although beetles were observed on the FDC sunflower, some disease resistance was evident.One of ONfungi’s targets this year is to do monthly tests on completed FDC material to chart the staying power and degradation curve of finished FDC, not yet put to use and in several storage modes. We are also using the microBIOMETER® to look at carbon sequestration in lawn soils.About ONfungi; ONfungi is a happy conglomeration of active volunteer folks. Their goal is to explore, through citizen science, the use of Johnson-Su fungal dominant compost (FDC) in improving soil, storing carbon, and enhancing plant health and nutrition. Learn more at ONfungi.net
Austin Arrington of the Plant Group
Austin Arrington of Plant Group NYC performed a research study on hemp’s capacity to sequester carbon. Austin utilized microBIOMETER® in this research. We originally had the pleasure of meeting Austin through Indigo Ag’s Terraton Challenge. Plant Group is a fellow semi-finalist and alumni.
Hemp has the promise of being a twofer: a financially successful crop as well as a carbon crop that increases soil carbon for carbon credits and increased fertility. Austin used microBIOMETER® to evaluate two organic fertilizer regimens for a hemp crop; an early fertilization during the vegetative phase and a month later during the flowering phase.
Honeysuckle Hemp 2021: Research Notes
One hectare of industrial hemp can absorb up to 22 tonnes of CO2 per hectare. The fact that industrial hemp has been proven to absorb more CO2 per hectare than any forest or commercial crop makes it an ideal tool for carbon farming (Vosper, 2011).
Two acres were hand seeded with Maya hemp grain on 05/23/21 in a silt clay loam soil in Council Bluffs, IA. Prior to tilling (with a rear tine tiller) and seeding with hemp the area was covered with white clover. The area was split into two zones that each received organic fertilizer at different times. The Early Fertilizer Zone was fertilized on 07/25/21. The Late Fertilizer Zone was fertilized on 08/08/21. Mega Green (2-3-2), the organic fertilizer applied for the study is derived from squid waste and was diluted with water for application across the field.
The microBIOMETER® spectroscopic tool was used to estimate microbial biomass carbon and fungal to bacterial ratio. Microbial biomass carbon is a measure of the carbon ( C ) contained within the living component of soil organic matter (i.e. bacteria and fungi). Microbes decompose soil organic matter (SOM) releasing carbon dioxide and plant available nutrients. The measurement unit of the device is ug C / g (micrograms microbial biomass carbon). Click here to read full study.
Calibration of microBIOMETER® to units of µg microbial carbon / gram soil
The gold standard of laboratory soil microbial biomass testing is Chloroform Fumigation and Extraction (CFE). The multiple steps, time, and labor involved with CFE require pricing at up to $500 per sample. CFE works by comparing the difference of chemically extractable carbon between two portions of a soil sample: One that has been treated to break open microbial cell membranes and expose the carbon-containing biological molecules to extraction, and one that has not. The difference in carbon for the two portions is reported as microbial biomass carbon (MBC), in units of µg C / g soil.
microBIOMETER® is calibrated to the same units by a different method. Estimates of bacterial dry mass converge at around one trillionth (1×10-12) of a gram (1 pg) for a 1 µm bacterium. We measured the area of microbes in known volumes of microBIOMETER® extract (both by manual counting on a hemocytometer and by digital analysis of micrographs) and calculated total microbial mass, which was then converted to µg / g for the whole 0.5 ml sample of soil in the extract. We found that on average, 0.5 ml of soil weighs 0.6 g when fully dried, independent of starting moisture content. The 1 pg dry mass per bacterium is 50% carbon, so we also had to account for that in our calibration.
Here’s an example of the conversion.
Let’s say that in 1×10-8 liter (10 nl) of microBIOMETER® extract we measured 240 µm2 of microbes. 240 µm2 = 240 bacteria equivalents (BE). 240 BE x 1×10-12 g per BE = 240×10-12 g of dry microbes. The volume of original extract is 10 ml (1 x 10-2 liter), and 10 nl of microscopically examined extract represents 1×10-8/1×10-2 = 1×10-6 of the total mass of the microbes in the extract. So 240×10-12 g microbes / 1×10-6 = 240 x 10-6 g microbes in the whole extract. 50% of the 240 x 10-6 g of microbes is carbon, so we have 120 x 10-6 g microbial carbon. We started with 0.5 ml = 0.6 grams of dried soil in the extraction process, therefore 120 x 10-6 g microbial carbon / 0.6 g soil = 200 x 10-6 g microbial carbon / gram soil, or 200 µg microbial carbon / gram soil.
While we arrived at µg microbial carbon / gram soil through a different method than CFE, it turns out our methods are on par with the CFE test. We compared measurements of µg carbon / gram soil via CFE and microBIOMETER® from 28 soils from across the U.S.
The slope of ~1 of the regression line indicates our units are on par with CFE, and the 94% correlation indicates that users can be confident that the $13.50 or less microBIOMETER® test gives results as accurate and informative as one priced $500.
We recently received the following questions from one of our customers and below are the responses from Dr. Fitzpatrick.
Part of my research is surrounding the soil organic carbon results we attained from microBIOMETER®, and I am wondering if someone from your team could provide more information on what this means relative to total organic carbon (TOC) in a sample and if they are comparable?
The literature shows a strong correlation between available organic carbon and microbial biomass carbon (MBC). Since your compost is not soil, the available organic carbon in your sample would be TOC and would correlate. MBC by microBIOMETER® is even better than that: a big number tells you that you have carbon and all the nutrients needed by microbes and plants.
Since MBC has correlations to TOC is there a formula or percentage to convert MBC to TOC? Or approximately how much MBC makes up a TOC number?
There is no formula to correlate TOC with MBC. TOC includes carbon that we consider stored as well as carbon that is easily available to microbes. Increasing easily available carbon for example by applying compost will increase microbes and eventually increase TOC, but as microbes rarely exceed 1% of TOC, it would have little effect on TOC short term. In long term stable systems we see a correlation but the correlation is not the same for example in forest as in agriculture as the capacity to store TOC is different soils under different conditions. In studying the effect of long term (40 years) different management systems at U. of TN on MBC and TOC, MBC by microBIOMETER® correlated with the TOC demonstrating the effectiveness of sustainable practice on increasing TOC and the positive correlation with MBC levels.
Does a high MBC usually mean a higher F:B ratio? And if so, could we draw any conclusions about carbon sequestration capabilities from that?
Generally as the MBC increases there is an increase in fungi. The soil food web is a balanced community. Some communities are more fungal dominated some less, but similar communities tend to have the same F:B ratio. It is generally believed that fungi, especially mycorrhizal fungi, contribute more to carbon sequestration than bacteria. This may be because glomalin is carbon rich and tends to sequester.
To further my understanding of soil/compost mixtures. I performed two microBIOMETER® tests. One test was on “active compost” which is compost in a medium stage of decomposition, and generates some CO2 and another one “finished compost” which is cured, ready for usage, and low CO2 production. However, I found that they had similar amounts of MBC and F:B ratio. Is this normal?
A study with microBIOMETER® at University showed a higher F:B in finished compost. The higher respiration/MBC indicates that your unfinished compost is still being digested — working microbes make more CO2. Holding MBC stable in your finished product is good.
Soil testing
Modern agriculture practices have led to the systematic degradation of the world’s soil and release of carbon into the environment. The effects are increased need for expensive and environmentally dangerous inputs (fertilizers, pesticides, and herbicides), the loss of fertile top soil, decrease in water holding capacity of soil and dangerously high levels of atmospheric carbon.
Farmers, industry, and environmentalists are looking for cost-effective and reliable ways to measure soil health, to assess impacts of progressive changes on soil and harvest management, and to measure carbon in soil. Before microBIOMETER®, growers have traditionally relied on expensive lab testing of soil. Many current methods are technique and individual lab dependent. Therefore, run-to-run and lab-to-lab variation can greatly affect consistency leading to increased variability. Current methods are performed in labs and the soil is aged and changed from the time of collection. Furthermore, lab tests are difficult to use in developing countries as they can cost upwards of $500 per sample. This makes the test prohibitive to some markets and limits the number of times a grower can test their soil.
Our mission at Prolific Earth Sciences is to enable soil stewards all over the world to use mobile technology and our low-cost soil test to assess regenerative soil practices, to improve soil health, and work towards increased soil carbon sequestration. microBIOMETER® equips growers with the data necessary to make decisions on which practices are the most cost-effective. Inputs such as fertilizers are expensive and changes to practice are risky. Monitoring soil microbial biomass inexpensively, in real time, can help a soil steward quickly assess if an input and practice is improving soil health and worth the investment. In other words, assess before you invest! We also envision microBIOMETER® one day being a powerful tool in the measurement and audit of carbon sequestration programs.
microBIOMETER® has been on the market for over 3 years with direct and distributor sales and currently has customers in over 20 countries.
Soil carbon is important to soil health because it enables microbial life. Microbes are able to obtain carbon directly from plant exudates, however, much of their carbon source is from the dead plant and plant derived materials that they digest. We harvest much of the above ground matter from crops, but plant roots, cover crops and various manures can provide additional sources of carbon and other nutrients for microbes. Pure carbon, for instance coal, is not something we add to soil to increase fertility. It is the soil organic carbon, the carbon originally derived from the living plant, animal and microbial sources, that predicts soil health. This is because it is food for microbes. Without fungi and bacteria making the glues that allow microbes to stick to soil and create soil texture, the soil becomes a powder that is easily eroded and does not hold water. Moreover, without microbes that are so tightly bound to the soil to store nutrients, the soil becomes barren.
Soil carbon begins as plant exudates and dead plant material and ends as humus, the molecular remnants of the bodies and refuse of dead animals and microbes that digested the plant material. Newly broken-down plant material is close to the surface and available to microbes as soluble organic carbon. Using this easily accessible carbon, microbes can multiply. Furthermore, carbon that is in microbes and other inhabitants of the soil food web can be viewed as a savings account. Turnover in the food web is rapid and these materials are being recycled. As organic carbon molecules become in excess, i.e., they are not rapidly recycling, they attach themselves tightly to minerals and clay. In this state they are more difficult for microbes to access. They begin to descend deeper into the soil becoming even more closely associated with soil particulate matter and can now be described as sequestered carbon. The amount of carbon your soil can potentially sequester depends heavily on the particulate matter of your soil. Some soils can accumulate as much as 20% others probably less than 3%.
Earth has surrendered 50% of its sequestered carbon to the atmosphere. How did this happen? As a plant starts to grow, it sends out exudates that stimulate the dormant microbes to start multiplying and working to bring nutrients to the plant. If there is insufficient soluble organic carbon available, the plant stimulated microbes will need to mine carbon from stored carbon sources. Over many years of non-regenerative farming, the microbes have depleted this stored carbon. Mineral fertilizers have replaced the microbes bringing minerals to the plants, but they do not provide carbon for microbial growth. Moreover, plants do not put out exudates for microbes when supplied with mineral nutrients – the stimulus for exudates is the need for minerals. The tragic outcome of low microbes is the loss of soil texture which leads to soil erosion and the inability of the soil to retain moisture.
You need to have all forms of carbon for soil health; plant exudates to stimulate microbial growth, newly digested matter, soluble organic carbon for the population explosion, and stored carbon for the poor times when the microbes need to delve into their reserves. You also need to store carbon by feeding the microbes carbon and replacing minerals in a manner that does not inhibit microbial growth. Sequestered carbon is 60-80% the remains of dead microbes.
The microbial population or microbial biomass (MB) reflects soil fertility. For over 2 million years, plants and soil microbes have worked together to create what we call fertile “soil”.
How do they work together? The plant supplies the microbes with carbon rich food. The microbes then mine the soil for the required minerals. Microbes can actually manufacture nitrogen and antibiotics that protect the plant from pathogens in return creating carbon stores that build soil structure and sequester carbon.
Like all good partners, what is good for one is good for the other, i.e., a healthy MB predicts a healthy plant. Therefore, supplying NPK directly to plants disrupts the plant microbe relationship – plants no longer feed the microbes and the MB decreases accordingly. Soils with low MB suffer from erosion, compaction, and poor structure. Sadly, this is how we have lost 50% of the earth’s soil.
Soil microbes, like all living things, need food. They need to be fed carbon and nitrogen from plants or organic matter so they can mine the minerals, P, K, Mg, Cu S etc. from the soil. If there is not enough of any nutrient, including the minerals that should be in the soil, it negatively affects the number of microbes; just as humans do not thrive when we are deficient in a critical nutrient.
Oxygen, water, and an agreeable pH and temperature are also important for soil microbes. Compacted soil is low in oxygen and microbial biomass. As soil dries, microbes die or become dormant. MB is much lower in low and high pH soils than in those that are in the neutral range. This is because most enzymes work best at neutral pH and all metabolism is enzyme dependent. MB also contracts during intense cold and heat. Plant roots require these same conditions
Microbes also need shelter to survive. Soil aggregates provide small cubbyholes that accommodate oxygen and water. It is in these areas where microbes attach themselves to be protected from predators. These predators are larger than they are; think of how little fish hide in coral. Not only are soil aggregates homes for microbes, they are homes built by microbes. The capsular material that microbes secrete to attach themselves to soil particles is long lasting. It binds the soil particles, therefore, creating aggregates that build soil structure and prevent erosion. These aggregates provide the water, oxygen and wiggle room needed by plant roots.
Furthermore, soil microbes build up carbon in the soil by producing humic matter. When microbes die, their bodies become stored carbon. This is good for microbes in the way that a savings account is good us. It is important for the soil as well because the humic matter increases soil structure. This allows more oxygen and water storage. It is also a resource that microbes can take a loan from before harvest when plant material is not being released to microbes. For too long we have relied on microbes borrowing from this humic carbon source and have released ½ of the soils stored carbon to the air as carbon dioxide. This has contributed to climate change and loss of 50% of earth’s soil. Microbes have always worked well with plants to create soil and they can help us restore exhausted soils back to fertility.
Increasing your soil microbes increases carbon sequestration. Carbon is stored in the soil as “humic materials” i.e. C,N,P,K etc.; rich organic matter which is the soil organic carbon or sequestered carbon in the soil.
The formation of humus, the final stable carbon, is a stepwise process. All organic carbon in soil comes from plants, either directly or via digested plant material. It starts with plant material being digested by soil microbes, or in the case of brown manure, being predigested by animals and further digested by microbes. The breakdown process begins with soil fungi and bacteria. As these microbes are fed carbon, they multiply. If fresh carbon stores are not utilized, they become attached to soil particles and become stored, therefore, less available as food sources. As microbes die, if they are not immediately cannibalized, their remains also become part of the more recalcitrant humic material.
Slowly, this humic material, which is as much as 80% the bodies of dead microbes, builds up. We measure it as soil organic carbon (SOC) and it reflects the carbon sequestered in the soil, but it also contains all the minerals and other plant nutrients. To increase SOC, the fresh organic matter required to feed the microbes and in turn the plant via the microbes, there needs to be an excess of the minimum required for a low microbial population. If there is an excess, the microbial population increases, and their dead bodies will increase the humic matter, in return increasing carbon sequestration. If it is not adequate, the soil microbes will be stimulated by the plant to mine the stored organic matter, which will decrease the stored carbon. It is not surprising that scientists have compared the plant/microbe/soil fertility index to economic models. A rich soil, like a rich man, has money in his pocket and money in the bank, for soil the currency is carbon.
This system is very much like our agricultural complex. There is fresh food, which we utilize within days, food we freeze or can, which requires freezers and can openers to access, and food stores (our sequestered carbon) that we maintain in silos as protection against disaster.
