Talking Dirt

By Andrew Lyell

One of the Zoo's many behind-the-scenes compost bins.

Have you ever felt the ground move beneath your feet? I don’t mean the regular earthquakes that Southern California experiences, but the soil that we walk on. It is teeming with life, and each square foot hosts billions of residents, wriggling throughout it. You might not literally feel it move, but with the volume of organisms in it, I would expect it to be writhing. Though soil is sometimes described as “living,” this refers to all the life that it supports. A major component of soil is inorganic particles that begin as rocks and boulders.

Different geological forces act on rock, breaking it down into smaller and smaller pieces. So thanks to the actions of wind and water, the stones you see on mountain tops will eventually make their way down through rivers and streams, tumbling over and over until they are gradually worn down to become sand, silt, or clay. Each of these has different properties, so they each react differently in soil. Sand is the largest sized particle, silt is smaller, and clay particles are the smallest. These three particles are found in varying percentages in different types of soil.

One of the factors that soil affects is water drainage. Those of you who garden with clay soil know how poorly water runs through it. As soil particles get smaller, the amount of space between the particles decreases, leaving no room for water to move. So with sand, the water will drain quickly, while clay soils drain slowly. Organic matter improves soil structure, water drainage, and fertility.

Compost and mulch are the byproducts of decomposing plants and animals. A menagerie of soil denizens (including fungi, invertebrates, bacteria, and viruses) helps break down compost into products that plants can reuse and continue the life cycle. Worms are particularly helpful in this process. They not only consume and digest dead plant matter, ultimately pooping nutrient- rich “castings,” but they also aerate the soil as they tunnel through it. Additionally, the slime that worms secrete helps to condition the soil and bind it together. It is also full of nitrogen, an element that is vital for plants.

The ground beneath your feet is the most fundamental part of any habitat, but it is also one of the most neglected and least understood. You can learn more at one of the composting workshops held monthly by the City of Los Angeles Bureau of Sanitation.

This post was originally published in the March 2013 issue of Zooscape.