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Re: [compost_tea] numbers

Hi Anthony - 

I'm out of time!  But here's a first pass at the explanation for you!  Back in two weeks!

Numbers of individuals in soil.  OK, here goes. 

That's not possible to say, really, for fungi.  A fungal individual is difficult to know for certain.  Plate counts mess up on that measurement - in general, plate counts give you "how many spores of fungi and pieces of hyphal strands were the fungi broken into when you shook your sample", which isn't really a useful piece of information. 

Colony forming units - CFU - do not tell you if the fungal propagule was a spore, a tiny piece of hypha, or a mat of hyphae.  You need to do biomass, that's all there is to it, when you are dealing with fungi. 

Especially when you want to compare fungi and bacteria, comparing numbers is just plain nonsense.  We could tell you how many individual strands of fungi are present in soil, but that is dependent on whether the soil was just plowed, or not.  Doesn't relate to anything useful. 

But what about bacteria?  Bacteria clump together, they like to form colonies.  Just like people.  People clump together in villages, towns, cities, etc..  The group helps each individual better.  Think of a bacterial colony as being like a neighborhood of similar ethnic people. 

Plate count approaches cannot separate all the colonies into the individuals, so plate counts always underestimate the actual number of individuals - but you don't know by how much.  How many colonies were broken up when you shook your soil sample in buffer?  How many were not, or were partially broken up? don't know.  So, what are you getting when you run a plate count? 

In direct microscopy, we count the individual bacteria that we can see, including the bacteria in colonies, measure length and width, and then using the typical density of bacteria in soil, determined over the years by lots of testing and which varies from soil to soil, season to season, we can determine biomass of bacteria in soil. 

We are working on differences in bacterial and fungial densities in the rhizosphere of different agricultural plants right now, so that will be put into the data that will be used to fine-tune the SFI report based on each plant that you tell us has been growing in the area you want to know about. 

A good test for a lab that says they are doing direct measurements, but are perhaps not actually giving good data because they don't work with the person who developed the direct microscopic techniques they purport to use, is to ask them how they figured out density of bacteria and fungi in soil.  What values do they use in their spread sheets, and how those values change with season. 

SFI labs direct that question to me, because I developed the knowledge.  Sharing that knowledge, having someone able to understand that level of seasonal change, and understand how to do the assessment, generally takes a minimum of Ph.D. in microbiology.  So, yes, other academics can tell you the reason you need to pay attention to this, but only by working with SFI labs will you get the knowledge that has already worked that one out. 

People who stopped by SFI and spent a week, or even a couple years, "training" with SF were not given this information.  They can't explain where each value in our spread sheets comes from, and of course, that's critical in order to change the seasonal parameters, the plant parameters, that need to be changed. 

Anyway, on to the numbers.  We explain numbers versus biomass in SFI courses, so, if this discussion is a bit too much, please come to one of those classes. 

Bacteria generally run about 1 million per gram (about a teaspoon) of dry weight of soil in conventional agricultural soil.  Typically a plate count will overestimate the actual numbers of bacterial individuals, because the plate count will include dormant stages of bacteria, not just the active bacterial cells.  That's a problem.  If the information you need is - how many functioning cells in my soil - then you cannot get that knowledge from a plate count. 

Bacterial numbers in HEALTHY agricultural soil, healthy defined by the plant can grow without pesticides or inorganic fertilizer to help it survive (not on drugs, if you will) are typically about 600 million per gram dry weight of soil. 

Numbers of bacteria per gram in a conventional lawn, maintained by a chemical service?  You may have only disease - causers, and you may have only a few thousand per gram.  Pesticides kill things.  Oh, surprise. 

In a healthy lawn, which is disease-free, so not requiring any pesticides, we can find up to 2,000 million bacteria per gram of soil.  But that better be balanced by a fungal biomass to balance nitrogen in a proper ratio to grow your perennial grasses. 

The proper biology does that for you.  You must get the ratio of fungi to bacteria correct, for the plant you want to grow, or you may be setting the stage to grow weeds better than the plant you want to grow. 

If that statement confused you, it may be time to come to an SFI class. 

In a field of soil (about 2 million lbs of soil in the top ten inches in an acre of soil), that's well into the billions of individuals of bacteria, and possibly fungi.  

You need to be very careful when someone is talking about numbers of individuals of bacteria or fungi that you get the units correct.  Did they say billions of individuals per gram of ag soil?  Then they are not correct. 

Did they say billions of individuals per gram soil in an old growth forest?  They are correct.  How productive a system are you talking about? 

If they say billions of individuals in an ag FIELD, then they MAY be correct.  In an old growth forest stand of trees?  They are being too conservative. 

And that's just bacteria and fungi.  what about protozoa?  Add them in. 

Nematodes?  Microarthropods?  You CANNOT have a healthy old growth forest without several hundred thousand microarthropods doing their thing, during the right times of the year. 

Seasonal processes going on there, and we need to make sure they are there, in order to have a healthy forest. 

Much to understand.  But not impossible, nor even all that complex, if you get an understanding of how it all works together.  There's a great deal of "well, of course that's how it works", once you have someone explain the functions of the different critters for you. 

Elaine Ingham
President, Soil Foodweb Inc.
SFI Corvallis, OR
SFI Port Jefferson, NY
SFI Lismore, NSW, Australia
SFI Hilversum, The Netherlands
SFI Cambridge, New Zealand
SFI Culiacan, Mexico
SFI Jerome, Idaho

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