Introduction: What is soil? Here's a hint: It's not dirt! Dirt is soil that has been disturbed or moved. It is usually rocky and lacking in the nutrients soil contains. Soil is a mixture of water, air, pieces of rock, minerals, and organic matter. It is the nutrient rich material that plants grow in. Wildlife depends upon soil and plants for food and shelter. We depend upon soil to grow our food. Without quality soil, agriculture cannot be sustained. Soil supports our infrastructure - buildings, roads, and bridges. Soils absorb and distribute water. They help filter our pollutants. Needless to say, we depend greatly upon rich soils!

Not all soil is the same. The type of soil that forms depends on many factors including the rock it forms from, climate, formation time, and topography of the land. Soil forms in layers, called horizons, from weathered rock. Soils will have different physical and chemical properties. Texture will vary depending on the sizes of the sediments the soil contains. Structure is how well soil holds together. Soil that clumps together too much leads to poor movement of air and water, or infiltration, throughout. Fertility describes how nutrient rich the soil is and how well plants grow in it. Soil pH is how acidic or basic the soil is. This will impact how well certain plants and crops grow in the soil. Color reflects the mineral and organic content of the soil. Darker colored soils are usually more nutrient rich than lighter colored soils. Scientists use all of these properties to help classify soils into twelve types called soil orders.

Try the practice questions to see what you know about soil.