Healthy soil is composed of sand, clay, and silt. These three ingredients are found in various proportions in all soil. Loamy soil can be found near the rivers in Eugene, but most of the soils in the other parts of the city have a high clay content. Healthy soil is permeable soil so that it doesn't retain too much water.
Permeability refers to the rate at which water drains through the soil.
Soil with heavy amounts of clay can be made more permeable by adding organic matter such as compost. Organic matter helps stabilize the microscopic plate-shaped particles of clay and keeps them from becoming compressed, allowing more rapid water movement within the soil. These pores determine the amount of oxygen and water that pass through the soil. When macropores are connected to the soil surface, they can allow the soil to become saturated during a rainstorm or irrigation, causing water to pool instead of draining away. Tilling the ground is a good way to improve the drainage and reduce the number of macropores open to the soil surface.