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.
Different methods measure different fungal and bacterial populations. The chart below, adapted from Wang et al review of 192 different F:B ratios, illustrates how three different methods came up with three different F:B ratios for Forest, Farmland and Grassland. Note that microBIOMETER® correlates well with the gold standard, microscopy. By plate culture, forest F:B is about 1/3 that of farmland, whereas PLFA forest F:B is slightly higher, and microscopy and microBIOMETER® forest F:B are 10 times higher than farmland.
Nature article reports that microbial biomass estimates by microBIOMETER® correlates with soil health and yield stability.
The microBIOMETER® soil test was used to report microbial biomass in a recent Nature publication*. Scientists Dr. Judith Fitzpatrick and Dr. Brady Trexler of microBIOMETER® collaborated with a University of Tennessee team headed by Dr. Amin Nouri. The team evaluated the effects on soil health and yield stability of 39 different methods of raising cotton over 29 years. The conditions tested included till, no-till, various cover crops and different levels of nitrogen fertilization.
The study found that the major impacts on yield were very dry or wet conditions, and low or high temperatures. The deleterious effects of these weather extremes on yield were mitigated by regenerative agricultural practices which resulted in adequate soil, C, N, soil structure and microbial biomass.
*Nouri, A., Yoder, D.C., Raji, M., Ceylan, S., Jagadamma, S., Lee, J., Walker, F.R., Yin, X., Fitzpatrick, J., Trexler, B. and Arelli, P., 2021. Conservation agriculture increases the soil resilience and cotton yield stability in climate extremes of the southeast US. Communications Earth & Environment, 2(1), pp.1-12.
Austin testing soil testing at a hemp farm with microBIOMETER®
PLANT Group is a team of designers, engineers, and ecologists. The company is building systems to connect humans and nature. In the process, they are soil testing at a hemp farm in Iowa, Honeysuckle Hops & Hemp.
First, through their partnership with Blue Forest Farms, the team at PLANT Group is using microBIOMETER®. They are utilizing the tool to research soil health and carbon sequestration implications of growing hemp.
Furthermore, Austin has an interest in publishing research on their alternate organic hemp production methods. microBIOMETER® is assisting them in collecting some “pretty cool data on microbial biomass and fungal ratios in the soil in response to these strategies.”
Meanwhile, the company recently launched a new line of hemp food products, Hemp Hearts. They grow each plant regeneratively. This includes a focus on soil carbon, biodiversity, and ecosystem health.
Did you know one hectare of hemp can absorb 15 tons of CO2 per hectare? Hemp’s rapid growth makes it one of the fastest CO2-to-biomass conversion tools available. Therefore, let’s stop cutting down our forests. Plant some hemp instead!
Lastly, please visit the PLANT Group website to meet the rest of the team and learn more about their business. And follow them on Instagram to keep up to date on their progress!
Informal science education is a key for community engagement and healthy gardening. Community gardening brings numerous benefits such as fresh produce, therapy, physical exercise, reduction in grocery bills, improvement of mood among many others.
“Last weekend I had the privilege to teach community gardeners on the importance of soil testing side by side with my very first student at NYBG Adult Education program (class 2015). Dr. Joan Basile is a clinical psychologist who has developed her own horticulture therapy program incorporating soil knowledge brining therapy & soil science & gardening together.” – Dr. Anna Paltseva, soil_expert.
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“While the microBIOMETER® results showed there is room for improvement, the result from last year’s beds also proved that composting and mulching practices are paying off in increased soil life. This means that sandy soil will gradually be able to hold nutrients better and better!” – Dr. Basile
The Biospheres, working through the CDA*, accompanies and trains farmers/agricultural companies in the agroecological transition based on a soil conservation approach. The group is also working on applied research projects and therefore on trials under real farming conditions in which they evaluate the impact of certain changes in practices on different indicators (biological, chemical, physical, economic).
“One of our primary objectives is that farmers succeed in putting biology back into their soils to ensure their natural fertility. We are therefore very interested in everything that lives in the soil, from earthworms and microarthropods to microorganisms (bacteria, fungi, nematodes). For us, microbial biomass is one of the most important indicators that help us understand soil biology. Fungal to bacterial ratio, which is a less documented indicator for the moment, remains interesting to observe in certain situations and is the object of real research by our R&D team to understand how best to interpret it.
We have been using microBIOMETER® for 8 months now to test the soil in different projects in our panel of biological indicators. microBIOMETER® provides us with quick and easy results on microbial biomass and F:B ratio which is a real plus for us. We can perform tests directly in the field and present the results to the farmers. Moreover, the affordable price of the analysis allows us to perform soil biology tests in projects where we had no affordable way to do so before.”
*CDA, Centre de Développement de l’Agroécologie, are affiliates dedicated to R&D and advisory.
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.
Jeff Lowenfels
Jeff Lowenfels, a valued advisor and member of our Board, was recently featured in the New York Times Sunday Magazine article, He Wrote a gardening column: He ended up documenting climate change.
For 45 years Jeff has written a gardening column for the Anchorage Daily News and over this time has helped adapt Alaskan growers to their much longer growing season. And in doing so has become a documenter of climate change.
Jeff joined Prolific Earth Sciences because he knew the only way to wean agriculture off synthetic fertilizers was to trust the microbes to deliver nutrients to plants. Jeff is the well-known author of the all-time best selling gardening book, Teaming with Microbes, as well as Teaming with Fungi, Teaming with Nutrients and DIY Cannabis all very readable, informative and available on Amazon.
Ariel White; Post-Wildfire Forest Reboot Kit
Ariel White, a ninth grader at Pretty River Academy in Ontario, Canada, utilized microBIOMETER® in their science fair project titled Post Wildfire Forest Reboot Kit.
The project was awarded first place at their high school and chosen to compete at the Simcoe County Regional Science Fair. At the regional fair, Ariel was awarded a gold medal, Best of Earth and Environmental Sciences, Best of Fair, The Dufferin Simcoe Land Stewardship Network Award, and was one of seven students selected to represent their county in the Canada Wide Science Fair where they won a silver medal!
About the project: Forest fires have increased due to climate change, causing forests to burn down at an unbelievable rate. Now we need forests more than ever, yet they have been taking years if at all to regrow. This project explores the question “how can we boost the speed of forest regrowth after forest fires?”. For phase one of this experiment, each plant was graded for performance using tests such as success-rate, growth-rate, compost-value, and self-propagation. For the second phase, it was seen what effect this plant had on the soil microbiome; which is key to healthy, speedy plant growth and isn’t evident after fires. It was concluded that the morning glory substantially increased the microbiome health from inevident to healthy, and had an almost perfect performance score. These results are very important to our world’s future as they could help to deter climate change and repair our forests and their diverse ecosystems.
Chiappetta Agricultural Company
We were excited to hear from our long-time customer Marcelo Chiappetta of Chiappetta Agricultural Company on how his microBIOMETER® testing has been progressing. Below is what he shared with us.
“Here in southern Brazil the past 5 years we’ve been working with biological agriculture and changing the way we see and manage our farm; more and more like an agricultural organism. Taking care of microorganisms, plants, animals and humans and focusing on producing high quality grains.
Fungal and bacterial ratio is fundamental to know how our soil is related to what crop we grow. And now, after starting to brew compost tea and using compost extract, microBIOMETER® is helping us measure and understand the right recipe of carbon and nitrogen related to the amount of fungi that we want to build in our composts before adding to the soil. We see that good microbial biomass along with organic matter is excellent for our soils.
In practical terms, we see biological flowering in crop fields and this is the proof that we are doing a great job with nature. Our soil is our bioreactor, and we need to feed it with the right nutrients. The Brazilian biome is rich on biodiversity and as farmers and soil guardians we have a responsibility to bring life back to our farm again in a sustainable way of producing food.”
Click here to read more on Marcelo’s soil testing.
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