(Perma)Culture and Sanity
They're making people every day, but they ain't making any more dirt.
Healthy, productive soil is not simply a collection of nice, fluffy minerals. More importantly, soil—as opposed to simple dirt—supports healthy, nutrient-rich ecosystems composed of an amazing variety of soil micro-organisms and small animals such as earthworms, pill bugs, earwigs, etc.
It is this soil life living in healthy topsoil—from microbia and fungi to the larger macro-organisms—which together act to decompose, absorb and store (by incorporating into their bodies) any organic matter left on the soil's surface. In fact, underground life in healthy topsoil is so active that there is typically a much greater mass of living matter below the ground than above it.
Without these rich populations of decomposition organisms (together with their accompanying chemical processes), dead organisms would not be returned to living nutrient cycles but instead would remain tied up and lost to further generations of life.
In the simplest terms, decomposition organisms living in healthy soil consume and break down fallen organic wastes until these wastes are chemically simple enough to be absorbed by and incorporated into plants. The decomposed wastes and organic matter are then able to reenter the above-ground food web as they are absorbed by plants, and then eaten by animals.
Conversely, subsoils (as well as modern agricultural 'soils')—with their dense texture, impoverished soil life and almost-nonexistent biochemistry—have little capacity to convert, capture and store dissolved organic or mineral nutrients, to absorb rainwater, or in general to support above- or below-ground life.
While clay by itself can absorb and hold significant amounts of dissolved nutrients, it cannot convert minerals or raw organic matter into those dissolved nutrients without the help of soil organisms. The process of converting organic matter into plant-available nutrients requires the communities of micro- and macro-organisms whose function is to turn dirt into soil.
Our nation's agricultural areas long ago became devoid of 'soil'—our food is now hydroponically-grown (i.e., fed by solutions of petro-chemicals in water). In response to the removal of micronutrients from our farms and the food they produce, the USDA—rather than directly addressing the cause of this crisis (dead 'soil' due to our system's failure to return organic wastes to farmlands)—simply lowered vegetables' stated nutritional value to keep in line with the impoverished realities of modern chemical farming.
Soil organisms also help maintain the soil's tilth or fluffiness with their subterranean burrowing, creating tunnels which help allow free entry of both rainwater and air into the soil. Tunnels are also created when plants' roots die after growing through an area of soil, and millions of minute, hollow water-holding 'tubules' are left in the soil when cellulose breaks down.
Between the tunnels left by earthworms and those left behind by decayed dead plants' roots and cellulose, a clod of healthy soil is as riddled with holes as a sponge—easy to breathe through, and easy for oxygen and rainwater to infiltrate. Collectively, these tunnels offer far more tilth (i.e., porosity and softness) than is produced by digging. This is because digging leaves many air spaces but no structure—most of the tilth produced in mechanically-turned soil is lost in the settling action of the first heavy rain.
In addition to supplying a healthy soil's myriad nutrients, the mulch of dead plant and animal bodies covering an active topsoil slows rainwater runoff, allowing the rainfall to enter the soil's tiny tunnels and be absorbed into the ground. Healthy soil admits 80% or more of the rainwater that falls on it—the exposed subsoils dominating the Southwest today, on the other hand, reject more than 80% of rainfall on average. Water absorbed into the soil contributes to productivity, whereas water in runoff is useful only to erode and carry more topsoil away from our farms and into our rivers.
Reprinted from (Perma) Culture and Sanity Website