Soil Carbon Q & A with Dr. Judy

soil carbon

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.

 

Improving soil health and carbon content

soil testing carbon
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 a complex creature.

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 Role Microbes Play in Increasing Soil Fertility

soil fertility

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.

Carbon Sequestration

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.

microBIOMETER® Soil Testing in New Zealand garden community

In learning how to develop healthy soil for healthy plants and people, Frans Plugge of New Zealand discovered the importance of increasing the fungi population in his garden and this led him to microBIOMETER®.

“The microBIOMETER® soil test makes measuring the fungi to bacteria ratio so easy,” Frans said. 

To promote the benefits of soil regeneration, Frans has started the community street garden using the principles of regenerative agriculture; minimizing artificial fertilizers, pesticides and herbicides.  Frans plans to take regular measurements of the fungi to bacteria ratio using microBIOMETER® to monitor his progress as well as create a great discussion point with members of the garden community, therefore, contributing to a healthy plant community.

Some of the microBIOMETER® results Frans shared with us for his home garden and compost:

  • Our compost.  1102 ug C/g, F:B 1.7:1
  • Veggie garden soil. 310 ug C/g  F:B 0.1:1
  • Purchased compost soil mix. 1299 ug C/g F:B 2.4:1
  • Soil from native bush. 469 ug C/g  F:B 0.8:1

The first photo pictured here is a bare clay strip that Frans forked loose but did not turn. He added a thin layer of garden compost along with a layer of soil sowing in ten different species of autumn crops; legumes, grasses, and cereals. Then he planted brassicas into the garden (second photo).

Over the years, Frans typically added compost and dug in green crop in the main vegetable garden, but had not had great success in yield. This autumn in the area the microBIOMETER® sample was taken from, he planted an autumn cover crop of 7-8 different species and a selection of brassicas amongst them. The idea is when the cover crop begins to go to seed, they cut at root level and drop as mulch (third photo).  Frans is hoping they can stop digging in an effort to build up healthy soil organisms.

Frans’ conclusions related to New Zealand’s potential to reduce its carbon footprint:

  • If all New Zealand farmers lifted their soil organic matter (SOM) by .25% per annum, we could offset all New Zealand’s annual GHG emissions including methane.
  • Globally, numerous farmers are lifting SOM by 0.5 – 1% per annum over many years.
  • Add in parks, recreation spaces, berms, gardens and Crown Land.

About Frans:

  • Completed his degree at Lincoln University in Valuation and Farm Management
  • Founded ECOsystems in 1995 with the vision “Saving Energy and the Environment” and the mission “To reduce energy consumption in commercial buildings by 50%”
  • Longstanding and current elected board member of the Carbon and Energy Professionals N.Z. (CEPNZ).
  • In 2018, established the Kata School to promote practices of continuous improvement that Toyota has used for 70 years. He is the current chair.
  • Attended and presented at Al Gore’s Climate Reality Leadership training in Brisbane and completedthe Kiss the Ground training on Regenerating Soils.
  • Currently focused on using the behaviours of Toyota Kata scientific thinking and experimenting towards a vision to develop the culture required to achieve the challenge of carbon positive.

microBIOMETER® testing soil and compost in the Netherlands

With a small R & D grant awarded from the Dutch government, Jo Ploumen of the Netherlands is using microBIOMETER® to determine fungal to bacterial ratios in vermicompost filled in a Johnson-Su Bioreactor versus residence time. Jo also uses microBIOMETER® to measure microbes and F:B ratio in select soil samples as a member of a garden club. He found the differences by method of gardening; organic vs fertilizer and bare vs covered soil to be striking!

“I like microBIOMETER® as it is a cost-effective tool with a high impact, potentially,” Jo said.

Jo’s impressive resume includes studying Chemical Technology at the Technical University of Eindhoven, employment at multinational AKZO Nobel as an R & D specialist and co-founder of Pulsed Heat BV. In 2019, Jo founded Ploumen E.S. Compost to begin research based on the findings of Dr. David Johnson. Johnson is the developer of the Johnson-Su Bioreactor which delivers a compost with very unique properties.

We are honored to have Jo as a valued customer, data collector and partner on our journey to increase awareness of soil health, regenerative practices and carbon sequestration!

Photo source: Taos News