Bacteria and Fungi are the primary decomposers in large scale composting. Bacteria have the best enzymes for utilizing available Nitrogen. At the same time, the bacteria seem to insist on a 'balanced' diet. When they use up the N within their "reach", they stop working. Being between 0.3 - 1.0 µm (micro-meters) in diameter... they have a very short "reach". Turning tends to homogenize the feedstock, putting more N within the reach of the bacteria. This is why just after turning there is usually a bacterial 'bloom' for several days, until the bacteria run out of N again.
To give you more perspective on how small bacteria are, assuming 1.0µm in diameter, it would take 25,000, shoulder to shoulder, to span a single inch. A modest handful of compost at 50% moisture is 90 - 100 grams. When we weighed out a handful, we recorded 93 grams. Now, let's get to some interesting numbers.
For years we've known that we need to be able to "check up on our microbial master composters", to quantify the active bacteria population, and in May of 2004, we put together the resources and started doing just that. The above chart shows some very interesting information. This is NOT just theory. These numbers come from assays that we have done in our own lab, examining samples using 1000X and Epi-fluorescence microscopy. This is the sort of information that we work with.
Being beekeeper also, we can relate to 2,000 bees on
a frame when we lift a frame out of a beehive. We can comprehend 3,000 cells in the
honeycomb on each side of a frame in the beehive. We have a very hard time relating
to 15.5 billion active bacteria in a handful of compost.
How are such numbers estimated? One gram of compost is put in 9 grams of Phosphate buffer, pH = 7.5. Then "serial dilutions" are done until we have test tubes with 1/10th through 1/million. Then some of that is filtered through a 20 micron filter (bacteria are at least 30 microns in diameter). The bacteria are visible under the microscope and they are counted in some of the grids on the slide, then based on that actual count, our computer spreadsheet estimate the number of bacteria per gram, dry weight, of compost or soil.
Bacteria reportedly work in the moisture film on particles. The more surface area there is, provided there is adequate moisture, the more surface the bacteria and other microbes have to work on.
Our bodies produce heat when we metabolize food. The same is true for bacteria. The heat in compost is surplus microbial metabolic heat. Thus, heating is an indicator of microbial activity. Bacteria are the primary heat producers. We assume that when a pile is not heating that the bacteria are not very active. The causes can be numerous. Lack of moisture, and lack of a balanced 'diet' within their reach, are two primary reasons. The most common cause of lack of bacterial activity is lack of oxygen. Could you work without oxygen?
The most efficient composters are aerobic thermophilic bacteria. "Thermophilic" means that they work best at temperatures > 90°F "Aerobic" means they must have oxygen.
How much oxygen do the bacteria need? We found that with a 750cfm blower on a 165 cubic yard research pile of compost that we were able to hold the oxygen level up at about 15%, as measured with an oxygen meter at five different locations in the pile. That is a little over 4.5 cubic feet of air per minute per cubic yard of compost. Of course the oxygen requirements vary with the number of active bacteria. Our research suggest that the bacteria can exhaust the N within their reach within a couple of days. Thus frequent turning is essential, IF we want to keep the bacteria active, and they are our primary decomposers. In really active compost, we've repeatedly needed to provide over 10cfm of fresh air, per cubic yard of compost, on a continuous basis to hold the temperature below 160°F, and the CO2 below 2%.
When a compost pile runs out of oxygen there is a major shift in the biology and chemistry within the pile. Anaerobic bacteria put out intermediate byproducts, many of which are both foul smelling and phytotoxic. "Assuming" that the compost pile is aerobic is not as good as confirming that it is aerobic by doing cross section profile oxygen monitoring. We have monitored passively aerated windrows at many different compost sites, and we have consistently found oxygen levels below 5%. That is why we believe in using forced aeration and monitoring the oxygen level.
Human digestion is probably a combination of both
aerobic and anaerobic bacterial activity. Clearly, human feces is not mature
compost. At the same time, responsibly composted, including at least 3 days above
131°F to kill pathogens, it can be made into high quality compost. We are NOT
handling any sewage sludge in our composting operations and have no intention of doing so
in the foreseeable future.
Reportedly ALL Fungi are strict aerobes; that is, they MUST have oxygen. While bacteria can out-compete fungi for Nitrogen as long as there is Nitrogen within the reach of the bacteria, once the bacteria have consumed the Nitrogen within their reach... the fungi then gain an advantage because the fungi can send out their hyphae to get water, nitrogen and carbon from different places.
While bacteria are very effective at decomposing many feedstocks, when it comes to cellulose and lignin, we understand that white rot and brown rot fungi are the most effective. Fungi reportedly have a C:N Ratio (Carbon:Nitrogen) of about 30:1. Bacteria reportedly have a C:N Ratio of about 5:1.
Bacteria feeding protozoa are very important in the soil foodweb. At this point we don't know whether they play an important role in composting. Since Protozoa are very important in the finished material, to cycle nitrogen for plant use, they are of interest to us from the viewpoint of finished product quality.
Bacteria and fungal feeding Nematodes are very important in the soil foodweb for cycling nutrients for the plants. At Mother Nature's Farms we are taking special steps to develop healthy populations of these beneficial nematodes in our finished products, to optimize finished product quality.