1. Definition of Soil

    A collection of natural bodies on the earth's surface, containing living matter, and supporting or capable of supporting plants.

  2. Limits

    1. Upper Limit- generally considered as air or water

    2. Lateral Limit- deep water or barren areas of rock, ice, salt, or shifting desert sand dunes

      lateral limit

      Sediments at depths greater than where emergent plants grow is not considered as soil.

      soil not a soil
    3. Lower Limit - difficult to define, but generally thought of as the common rooting depth (shallow in deserts, deep in humid tropics) of the native perennial plant

      lower limit

  3. Two concepts of Soils:

    1. Pedology - study of soil as a natural entity - origin, classification and description.

    2. Edaphology - study of soil from the standpoint of plant growth.

    A person's concept of soil depends on his/her viewpoint and experience.

    1. Engineer - loose or broken rock material at the earth's surface. This material can be used for building purposes.

    2. Geologist - highly weathered rock. Part of the material that makes up outer mantle of the earth.

    3. Horticulteralist - material that needs sterilizing and modification before using for plant growth in greenhouses.

    4. Turf Specialist - material that supports foot and cart traffic, grows grass, and will provide a good fairway or putting surface. Will modify it to suit their needs.

    5. Farmer and Agronomist - material at earth's surface with biological, chemical, and physical properties that enable it to support plant growth.

  4. Types of Soil

    There are two general types of soil:

    1. Mineral
      • forms from rock and sediment
      • most soils form from minerals and are called mineral soils
    2. Organic
      • forms from peat, muck, and plant remains
      • may form in swamps or very wet areas
        example--the blacklands of NC

  5. Mineral Soils

    1. 4 major components of mineral soils

      • Mineral material
      • Organic Material
      • Water
      • Air

      soil components
      Ideal Soil

    2. Mineral soils are made of:

      1. Solids

        • mineral part -- mineral particles, sand, silt, and clay, fertilizers, chemicals
        • organic part -- plant material, decomposing microorganisms, worms, peat moss

      2. Pores
        • Air
        • Water

      All of these parts together make up soil. Since soil is a medium for plant growth, we have to ask what is the best mixture for plant growth. What would be the ideal soil for plant growth?

      When a balance is not maintained problems occur:

      • too much water -- flooding
      • not enough water -- dry soil, problems that we see now.
      • not enough air -- compact soil that will not grow plants

      Soil Science Glossary