Friday, June 26, 2015


The Microbiometer™ is an on-site test that allows you to estimate the number of small microbes in your soil to see how it works go to  Microbiometer Demonstration.

Adequate numbers of these microorganisms assure you that the soil is healthy.  This test was developed by me (I hold 12 patents in medical diagnostics) in conjunction with James Sotillo who is a landscape architect using organic practices, under a Quality Assurance Grant from the National Science Foundation.  

When James came to me with the issues, I was intrigued,  as President and owner of a company that sold FDA approved drug of abuse tests I am very familiar with quality control:  I responded to was Sottilo’s desire for quality control tests and standards for soil, compost and soil amendments.  Currently the test is being evaluated in 6 states and Japan.

I answered some questions today from a user interested in knowing why the results of Microbiometer™ vary from those you would get using Microscopic count as taught by Elaine Ingham.  Here are my answers.  Please feel free to comment and ask questions.

The reason James asked for a test was that the microscopic method, in addition to being difficult to do in the field, is inherently error prone.  The Ingham method involves dissolving soil in water and then microscopically analyzing it for Microbes by looking at 10 fields.  These are the variables that affect microscopic counting by the Ingham method:

The Ingham sample by microscopy contains many large particles -- small microbes attached to large particles cannot be seen.  Most bacteria are attached to something, if they weren’t they would wash away.  Nutrients added to soil in bacteria stay in the area they are sprayed because the bacteria quickly attach to soil particles and are not washed away (like most of commercial fertilizers).   

Our extraction fluid and whisking was optimized to separate microbes from the soil particle.   You will see more microbes after extracting.  One way you can confirm this is to microscopically look at the extraction fluid after settling and before filtering.  I am sure you will see more microbes than you do in your soil sample.

When you measure the number of microbes of a certain size <10 um in diameter by turbidity, you are examining a large population.  When you observe microbes in ten sites you are looking at a much smaller population and so we observe that the Coefficient of Variation (CV) for Microbiometer™ is less than half that for microscopic count.

An additional variation for microscopy is that no 2 people will count the same number.  James has seen results from different labs on the same sample vary 2-4 fold.

For counting we use the hemocytometer at 400x.  The hemocytometer is used for counting blood cells.   The slide which costs upward of $100 has been sectioned into squares of known volume.  The volume of each hemocytometer square is exact.  We validated our test following the approved protocols for this highly accurate medical laboratory approved method.

We correlated the Microbiometer™ test results with a count of the microbe solution.    So if you microscopically examine the Microbiometer™ filtrate then you will see that you extracted more microbes than you saw with the Ingham method -- the Ingham method is not giving you the whole story. 

Next time I will post the results of our research on Compost Tea and growth of sod. 

Tillage vs No Tillage

Just read an interesting paper* that I obtained from Ellen Kandeler’s site on ResearchGate.  I really enjoy following her.  She is one of the authors of this paper that summarizes a 5 year experiment that measured the effect of tillage vs no tillage on microbial activity and the mineralization of Carbon and Nitrogen.  The results seem confounding to me.  When the soil was amended with 1% plant residues, the activity of the microorganisms was higher in conventionally tilled soil than non-tilled as was the amount of Nitrogen mineralized.  However the final outcome, i.e. the amount of Organic carbon released into the top 20 cm was the same in both samples (It was higher deeper in the soil in the tilled soil and higher in the top 5 cm in the untilled).  It appears to demonstrate that while more C and N can be mineralized in the tilled soil, it is lost to the subsoil more rapidly so the outcomes are the same.
So why are the microbes working harder in the tilled? More oxygen?   
I am puzzled by the emphasis on microbial activity in the academic literature.  It seems clear to me that many microbes are capable of senescence for probably years and only become active after conditions favor their activation.  Indeed in this paper, they demonstrate that amending the soil greatly increased the observed diversity of the microbial DNA seen – obviously these microbes were in the soil and ready to multiply when the conditions were appropriate.  Other researchers have shown that the microbial diversity of soils is remarkably unrelated to total population numbers or microbial activity. Using Microbiometer™ we see higher levels of microbes in spring, lower in summer – as well as observing higher levels of microbes in richer soils. 
*Assessing the effect of management practices on soil microbial communities in a Vertisol using enzymes and 15N-DNA stable isotopic probing techniques.  Miguelia Espana et al. 2006.  Conference on International Agricultural Research for Development.