The results of how micronizing reduces particle size are evident from the samples above: Vermicompost (at left) and Micronized compost (at right).

WP2o

Micronized Compost M ICRONIZED is a relatively

new term as applied to soil or compost. Micronization means

"to make micron-sized". But there's a problem with terms here. The term, "micron," is used in the phys- ical sciences, but not in the biologi- cal sciences. As several of my col- lege professors told me, "There's no such word as 'micron'. It's a non- sense term. Only engineers use it." This comment might lead you to suspect that engineers and biolo- gists don't spend a great deal of time communicating.

So, what term do biologists use in- stead of micron? Micrometer is the correct biological term. A microme- ter is one millionth length of a me- ter . Chop a meter into one million equal size pieces; one of the units is a micrometer. That's what most people mean when they use the term micron - a millionth of a meter, or more correctly, a micrometer.

The term micronized would then lead people to believe that each indi- vidual grain produced is on the order of one to perhaps several microme- ters in diameter. The important question becomes, would being crushed to that size harm the organ- isms on the original larger size piece of compost? Secondly, does crushing to that small size change the organic matter composition? Thirdly, why would you want to crush something into that small a size? What benefit is there from doing that?

The reason for micronizing com-

And Microbial Life In Compost What is the impact on living organisms after micronization? What happens to the "good guys and bad guys"? How do dormant organisms recover? These are some questions answered in this forum.

Elaine R. lngham

post is that by crushing into small micrometer diameters, the compost can be suspended in water and ap- plied through drip irrigation, over- head sprinklers, sprayers, etc. Com- post is much easier to apply using water delivery systems than having to use big trucks and shovels.

However, crushing something into tiny bits generally kills any liv- ing organism that gets in the way. Thus, if you require biology to be present in order for compost to do

the good things we expect from com- post, crushing i t into small-sized grains isn't going to benefit the life in the material.

Benefits Of Compost In previous columns, two major

benefits of compost were estab- lished; that compost contains a huge number of beneficial soil organisms and the food to feed those organ- isms. Are either harmed by the pro- cess of micronization? Consider the

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sizes of organisms in compost. Would crushing to small size crush the individuals, and thus reduce the number of organisms present?

Individual bacteria range from 1 to 10 micrometers (pm) in length or in diameter. Virus are smaller, a hundred to a thousand times small- er than bacteria and are typically measured in nanometers (nm) - a meter cut into a billion equal size pieces or 109 equal units. I t takes an electron microscope to resolve viral particles.

A fungal hyphae is bacterial size in width (2 to 10 pm) but because

fungi grow as long strands or pipes, they can be up to hundreds of feet long, and visible to the naked eye if hundreds of individual strands clump together. The largest organ- ism in the world is a fungus. I be- lieve there's a competition going on between Michigan and Wisconsin as to which state has the larger fungal individual, but either one is bigger than the biggest whale.

Protozoa are single-celled organ- isms, but they come in the range from 5 to 500 micrometers (mm) in diameter. The largest protozoa are visible to the naked eye. The ones

that form colonies are easy to see. Most nematodes are visible - just barely - to the naked eye, but be- cause they are transparent for the most part (unless they eat some dark-colored food), they are impossi- ble to see against the background of soil organic matter or soil particles.

When compost is "micronized", i.e., crushed into micrometer-size pellets, that crushing process will harm just about everything in com- post, except for virus. Not only are individual bacteria, fungi, protozoa and nematodes crushed and killed, but whole populations will likely be removed. This removes the major benefit that distinguishes compost from dirt. In addition, when prepar- ing compost, or soil for microniza- tion, it has to be dried, and drying kills an additional set of organisms. What's involved in the process of re- moving water? Drying a living cell destroys the ability of enzymes to function; they will be denatured.

Does removing water from com- post kill the organisms? Not neces- sarily. If you remove the water from between the nonliving components of the compost, not from the bodies of the organisms, and do the drying slowly enough, the organisms just go to sleep. But in most cases, in mi- cronization processes, field-moist compost is dried within a day or two to bone dry levels. This will kill some of the organisms.

Many business people will say this is a good thing, because during shipping, you don't want live organ- isms. Living organisms evolve car- bon dioxide so that a sealed package will swell up and explode, and use oxygen, so that the material goes anaerobic. One or the other, or both, are problems.

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Is it more the good guys or the bad guys that can't tolerate being mi- cronized? Some of each. Some good guys can't tolerate being dried and crushed; some bad guys can't toler- ate the same things. As a broad gen- eralization though, the bad guys are more tolerant as a group than the good guys taken all together.

Does that mean you always get mostly the "bad guys" left after you micronize? No! Absolutely not. If you have no "bad guys" to begin with, there will be no "bad guys" af- ter micronizing. If you have just a few bad guys when you start, you have a larger percentage of bad guys relative to the whole after microniz- ing. But if you start with a large number of bad guys, then the prob- lem will be overwhelming when you are done.

Quality is the point. Start with quality compost, you'll get quality out the other end. Start with poor bi- ology, you will have terrible stuff when you finish. So, the biology changes when compost i s mi- cronized. The set of beneficial or- ganisms is decreased. It is not possi- ble to get the same composition from micronized compost as was present before the micronization process. If healthy, happy, good compost was used, what comes out after being crushed will still be better than a poor-biology compost, but if it wasn't great stuff to start, what you get may be really bad. The starting quality is very important.

We have tested compost before and after micronization for active organisms. Immediately after mi- cronization and for several weeks following, we found very, very few active organisms.

Defining "Active" What does active mean? It means

that set of organisms which are tak- ingup measurable amounts of foods, using measurable amounts of oxy- gen, and producing a significant amount of carbon dioxide. Active or- ganisms are those actively doing work. I t could be any one of a num- ber of kinds of work, but a measur- able amount of work is being done in a short period of time.

Being active is quite different from being viable, or living, or be- ing alive. Dormant organisms are sleeping but living organisms - they can return to being active when conditions are right. A sleep- ing human being is not active, but will become active when the alarm rings in the morning.

The difference between being alive and being active is one of de- gree. A marathon runner is active,

doing a great deal of measurable work. A student dozing during a lec- ture is not active - no measurable work is being done. Both the marathon runner and the student are alive, however. The student is in a condition of dormancy - not very stressful dormancy however, be- cause it is easy to wake up from a light doze.

Dormancy that is stressfully im- posed can be difficult to live through - for example, when a person falls into extremely cold water and goes into cold shock, their heart stops, and brain function is so minimal as

to be undetectable. If treated prop- erly, soon enough, there are ways to successfully bring people out of that stress-induced cold shock with little or no apparent damage.

Is micronization like going to sleep, or like being tossed into freezing water? Probably more like being tossed into freezing water. Micronization is a great shock. Many of the organisms do not sur- vive the process.

How many individuals are lost of each organism group? Probably 90 to 95 percent of each organism group in the compost to start with

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are lost (data from our studies of the active and total biomass of organ- isms before versus after microniza- tion). If compost is good to begin with, a loss of 90 percent of the or- ganisms may still be good compost. But most compost is not that high in organism numbers.

Consider also t h a t aggregate structure is nearly completely de- stroyed because of the micronizing process. How quickly can that be re- built once water is added? If it's good compost, within a few days. But for compost that started with a poor set of organisms, or compost with little food diversity in i t - structure may never be regained.

Protection Against Negative Potential How can you protect yourself

against the problematic factors in- volved with micronized compost? Simple. Insist that the manufactur- er show you what was in the com- post before they micronized it, and what was in the compost when i t was done micronizing. It might be wise to test some of the micronized compost on a small amount of your land before using i t on all your land. Transpor ta t ion of a dried, mi- cronized compost might be cheaper, but you need to know if it's good compost before using it.

You can send samples to labs such as Soil Foodweb Inc. or to BBC Lab- oratory Inc. for testing. Different labs look a t different kinds of as- sessments. BBC looks a t diversity as measured by spread plate counts or Biolog counts, while Soil Foodweb Inc. does direct microscopic determi-

Table 1. Biomass of each organism group in the soil/ compost food web before and after micronization Pre-or Post Active Total Active Total Protozoa Nematodes Micronization Bacteria Bacteria Fungi Fungi F, A, C (see below)

Pre- 43.7 ug 179ug 12 ug 163 ug 71, 711, 5.3B micronization 1 25, 346, 60 2.2 F

Post- None 1 Ug None None 0, 0, 0 0.5 B micronization 1 detected detected detected

Pre- 31.9 ug 459 ug 41.2 ug 595 ug 43, 220, 10.3 B, micronization 2 130, 527, 205 1.2 F

Post- 1.3 ug 73.5 ug 0.03 ug 1.8 ug 0, 5, 0 None micronization 2 detected

Desired 10-30 150-300 2-10 1 50- 10,000, 50-1 00, Range Ug Ug Ug 1,000 ug 10,000, no root-

20 - 50 feeders

Protozoa = F stands for flagellate numbers, A for amoebae numbers, C for ciliate numbers. Nematodes = B stands for bacterial-feeder numbers, F for fungal-feeders, R for root-feeders, and P for predatory nematodes (beneficials). Desired levels of organisms in good compost are given in the bottom row. All assays were performed by Soil Foodweb Inc. using direct microscopy methods.

nations of active and total biomass. In the case of whether the compost was good before micronization, and whether it lost anything really im- portant during the whole process, ei- ther lab will give good information. I t might actually be important to know both sets of information.

While there is no standard for size of particles when micronized, the range is five or ten micrometers to 100 micrometers. The exact size of the sieve used to produce the materi- al should be given on the product la- bel. One west coast composter uses 500 mesh size to sieve his compost

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once it has been ground; 500 mesh re- sults in 25 micrometer size particles.

Micronizing always reduces or- ganism numbers and species. Re- duction in numbers, or even species, however, may not be a problem. If there's excellent diversity to begin with, the final compost - after com- ing out of the dormancy process - will still be very good.

Table 1 lists some numbers of com- posts before and after micronization. The standards for good compost are given in the bottom row of the table, so you can see what organism num- bers are needed in healthy compost.

Recovery is determined by the kinds of food resources ~ re sen t . Bac- teria will recover if thLbacteria1 in- oculum was not badly damaged by micronization, and bacterial foods are readily available. Fungal recov- ery will occur if the fungal inoculum was not badly harmed and fungal foods are available. Most of the time in microbized material, the inoculum is not available although the foods are, so recovery does not occur rapid- ly. An inoculum is required, and that 's where a good compost tea might work quite well.

Recovery will begin as soon as wa- ter becomes unlimiting. As noted above, typically compost is dried in order to micronize it, so recovery does not start right away in most cas- es - not until the micronized com- post is added to soil or potting mix, or something else that is moist. H

Elaine R. Ingham is president and di- rector of research at Soil Foodweb Inc. based in Corvallis, Oregon. E-mail: info@soilfoodweb.com.