There are two important places where compost happens in nature: the forest floor and inside stomachs.
The forest floor is a slow, sweet smelling compost pile we call duff. Duff even sounds muted and mysterious, a substance with tiny secrets and tantalizingly familiar smells. Leaves created through the miraculous process of photosynthesis—a process made possible by a bacteria containing chlorophyll that can capture light to make energy and food—fall back to the earth and are broken down by earthy critters into smaller and smaller pieces until they become food for soil microorganisms. This transformation has sustained forests for thousands of years.
The first shredders.
could you hear them if you paused,
ear to the ground, like the popping sound
of fish munching on coral underwater?
All of Mother Earth is being savored,
tasted, taken in, from forest to ocean to farm,
teeth and jaws gnawing away on our giant earthcicle,
passing particles through guts, working them deeper
and deeper into the ground until what once was leaf or twig
or even beetle or bone has become so small that soil microbes,
bacteria and fungus and slime mold, are able at last to access energy,
metabolize fallen sunspots, release stardust
back into soil where tree roots are waiting like open hands
to carry nutrients up and up to the canopy to be
knitted into next year’s leaves.
These microscopic bodies live, transform, and die without being seen in order to move the wheel of life forward. To take what is dead and transform it into a spark of life. A wonder. This is bodily, physical, and it can make us uncomfortable. It can turn our stomachs.
And our stomachs are the other place compost happens in nature. Stomachs and intestines combine to make an oxygen deprived compost tank inhabited by millions of microorganisms. The most efficient stomachs belong to ruminant (“room-in-it”) animals. They include sheep, goats, giraffes, deer, and llamas. Ordinary as they are, the inside of a ruminant’s stomach holds another one of life’s great mysteries. Ruminants can miraculously turn plant nitrogen into protein with the help of bacteria that scientists believe to be over 3.6 billion years old (archaebacteria), fungi, and protozoa.
Cows are the most widely known and underappreciated ruminants I know. With a four part stomach—the rumen, reticulum, omasum, and abomasum—cow manure is the best example of barrel turned compost on four legs. The first compartment of a cow’s stomach, the rumen, is the size of a barrel. It can hold up to 40 gallons of material and 25-30 gallons of salt-filled saliva are sent down there every day to balance the rumen’s pH. Just as in a compost pile, the smaller the fiber the more completely and efficiently it composts. So, what goes into the rumen is often sent back up for further chewing, for rumination.
Perhaps the bovines ruminate on their bacterial partners, how their partnership came to be.
Cows eat raw grass but, ultimately, they are feeding the microbes that live just down the tracheal street. Those toothless wonders need the grass to be chewed for them before they can get to work. On the forest floor, beetles and worms do the work. In a stomach, the organic material arrives pre-chewed, opening the way for them to extract all kinds of nutrients from it. Some they give to the cow, but a lot of it they keep for themselves, to give them energy and to make protein for their bodies. The microbes living inside the cow turn nitrogen stored in plants into protein, not the cow.
If you were looking for them, look no further, they reside in the rumen of ruminants. Ruminating on plant-filled sunshine. They will double in number every hour, and after a long life of a few weeks, the spent microbes are washed away into the cow’s intestines to be food for the cow. Seventy five percent of all of a cow’s protein content comes from the bodies of ancient microbes.
McDonald’s (the hamburger patty and the cheese), that charcuterie board at the winery (the cheese and the wine), the Greek yogurt for breakfast, all of them made possible by ancient microbes living out their lives inside cows.
Human stomachs don’t have the ability to turn nitrogen into protein, but we rely on a similar microbial partnership. Just a thimble-full of large intestine fluids contains up to ten trillion microbes. Without them, we would be unable to make K and B vitamins. And even our own humanure is a precious resource. When handled properly and with care, we can compost our own waste to use on trees, shrubs, lawns, and even agricultural crops, closing our nutrient cycle and saving millions of gallons of water by not flushing this resource down the toilet.
Our bodies have grown from the soil as much as our food has, and the microbes that make nutrients and proteins available to plants and cows and us are also waiting for us to give them our leftovers in a relationship of reciprocity. They do not care if what we give them is moldy or halfway chewed. They have no preference for a month-old piece of dried macaroni or a week old, uneaten scrap of a tostada. They only need the right conditions to break it down—the conditions found in a cow’s rumen, our own digestive tract, and the forest floor. Compost piles are a kind of external, symbiotic, second stomach in teh backyard. The same conditions that we create in our compost piles—a warm, moist, aerated mass of carbohydrates and proteins large enough to house bacteria and fungus, undisturbed for a while so they can do their alchemist’s work–breaking down our leftover food into exactly what the soil needs to grow more food. Humus.
When we add compost back to the soil, its pulse quickens. What were once food scraps have transformed into a plant root buffet, the positive and negative charges that electrify the ground, begin to stir, poised, then grow, organize, coalesce, take form, take root, reach for the sunshine to be plucked by teeth or fingers or the header of a combine, harvested and reformed into food again.
We make soil food. Soils make we food. We feed each other.
 Jenkins, Joseph. Humanure Handbook: A Guide to Composting Human Manure. 1999. Joseph Jenkins, Inc.: Grove City, PA.