The Real Dirt on Soil (Part 1 of 2)

In last week’s episode of Nature Minute I pointed out that the wildflowers at Mount Rainier support an ecosystem. Plants are the base of the food chain. We all know that plants convert sunlight and carbon dioxide into food energy. Water is also necessary. But commonly overlooked as essential to all life is soil.

What is soil? More than just dirt, it is a mixture of mineral and organic material that develops over long period of time. Geological and climactic forces and chemical reactions break down rock to form the mineral side of soil, while decomposing plants and animals supply the organic material.

Plants generally don’t move a lot so soil is important because it gives them a place to “put down their roots”. Many plants live on land, and those that do absorb their water from the soil. But soil is where the food chain begins. Look at the nutritional information on a food package. All those minerals start out in the soil. Plants absorb them and they move up the food chain into your chicken noodle soup.

Not all soils are created equal. Parent material (the rock which weathers into soil), organic composition, water, and climate all affect the soil. There are 12 orders of soil, and each order is further divided into groups, families, and series. Each type of soil is suitable for different types of plants.

The official soil profile for my location in Eatonville shows a great deal of sandy loam. Sand, silt, and clay are different particle sizes in the soil world. Sand is the largest and coarsest, silt is smaller and finer, and clay is the smallest and finest. Sand is porous and gives soil its ability to drain water. Clay particles stick together (if you’ve done arts and crafts with clay you will attest to its stickiness) and block drainage. The diagram below shows how the different particle mix to create different soil textures.

In my travels through nature working with amphibians, my biggest concern with soil so far has been whether or not wetlands are present. The three factors that determine whether or not you are dealing with wetlands are: 1 hydrophytic (water tolerant) plants, 2 hydric soils, and 3 hydrology (water movement). Hydric soils are characteristic of wetlands because they are flooded or saturated long enough to become anaerobic (lacking oxygen).

While plants are the base of an ecosystem, it is soil that determines the makeup of the ecosystem. You can overlook its importance and even walk all over it, but soil is another way that everything on the planet is connected. Next week is Part 2 of soil. Stay tuned!

This week’s soil information is courtesy of my soil science textbook Soil Science and Management by Edward Plaster.