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.

 

Soil testing update from Brazil

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.

Choosing an Arbuscular Mycorrhizal Fungi for your Plant

Arbuscular Mycorrhizal Fungi (AMF) colonize 80% of crops. Their effect on plant growth can be positive, neutral or negative. It depends on many factors including the crop species and genotype, the species of AMF, and the characteristics of the soil. A low pH favors colonization of the plant by AMF while application of chemical fertilizers, especially phosphate, inhibits colonization by AMF. In the absence of chemical fertilizers and in the presence of low levels of pH, AMF provides the plant with phosphorous. AMF can extract P from rocks so it can get P from soil that tests low for P.

AMF can dramatically increase plant yield and resistance to pathogens and drought, as well as decrease irrigation needs and sensitivity to salinity. Thus, AMF can be of great assistance in transitioning from conventional to sustainable/regenerative agricultural. There are now many suppliers of AMF but there is no guarantee that any one product will be optimal for your crop and your soil.

The new microBIOMETER® test, which estimates fungal to bacterial ratios in soil, can help you decide which AMF works best with your plant and soil because it can detect colonization of rhizosphere soil for fungi within a month of AMF application.

Leifheit, E. F., Veresoglou, S. D., Lehmann, A., Morris, E. K., & Rillig, M. C. (2014). Multiple factors influence the role of arbuscular mycorrhizal fungi in soil aggregation—a meta-analysis. Plant and Soil, 374(1-2), 523-537.