Soil Composition and the Nutrient Cycle

Soil consists of Inorganic Matter (sand, silt, and clay), Organic Matter (fallen leaves, roots, and decomposing plants), and Microbes (bacteria and fungi). In addition to the soil, there needs to be plants and leaf litter (mulch) for a healthy system. If it lacks any of these things, the Nutrient Cycle plants rely on will be incomplete. The inorganic matter contains all the minerals needed for healthy plants. But in most cases they are not water soluble. The microbes convert them to water soluble forms. But microbes have several needs that have to be met first. They mostly eat the sugars in dead plant matter, and break them down into a sort of compost as a byproduct of this action. They need this matter to live. They also need shade, from either plants or from the leaf litter; preferably both. They also need water to live. Leaf litter holds rainwater by shielding it from evaporation. Organic matter in the soil also holds water like a sponge. Fungi form mats of mycelium that may extend over very wide areas. The world's largest living thing is a single fungus that lives in the Pacific Northwest of the US.[See "6 ways mushrooms can save the world" by Paul Stamets.] Those mycelial mats in the Mychorizae family distribute water and soluble minerals to plants in exchange for sugars. Meanwhile, some types of bacteria turn nitrogen (N2) from decaying plant matter and the air into ammonium (NH4+). Without this function, plants could not grow at all. They need ammonium to grow leaves and produce chlorophyll.

In places where people have destroyed the nutrient cycle by depleting the organic matter in soil by ploughing, chemical fertilizers dominate. However, this has lead to more problems than solutions. The problems with chemical fertilizers are several. Firstly, they contain salts, and salting the soil kills remnant beneficial microbes. Secondly, chemical fertilizers are water soluble as is and most are not time released. When it rains, these run off and more fertilizer must be applied. The runoff presents its own set of problems. Besides increasing salinity in freshwater streams, it also causes algal blooms*.  *http://www.epa.gov/nutrientpollution/harmful-algal-blooms