What's Happening Below The Surface?

Tree growth takes place not only above the ground, but below. The nutrients necessary for plant growth are available under only very specific conditions for each tree species. Trees have adjusted after great lengths of time to very specific environmental conditions that existed long before humankind came on the scene. When we place a tree in an urban setting, we need to see that its needs are met. The site that a tree lives in will be modified by the tree, if the situation is not hostile. Our intent here is to determine the soil conditions around trees that are already planted and growing.

Soils differ widely over even a small area. Good soil will be composed of 45% mineral and 5% organic matter with the other portion equally divided between air (25%) and water (25%). Large populations of microorganisms, insects and arthropods, also occupy the soil and need air to survive.

Soils are generally composed of more than one layer or horizon. The soil color and compostion distinguish these layers. Using the enclosed resources, or your textbook, find out more about the structure of soil. Soil texture refers to the size of the particles that make up the soil. These five (from large to small) are large stones, gravel, sand, silt, and clay.

This exercise will familiarize you with the technique of soil sampling. Measuring different soil layers will aid in determining the soil composition in your area.