Soil

Mechanical and chemical weathering of rocks form soil. Soil covers much of the land on Earth. It is made up of minerals, air, water, and organic material. Soil provides a substrate for plants (roots anchor in soil), a source of food for plants, and a home for many animals. A scientist who studies soil is called a pedologist.

Types of Soil Many different types and each one has unique characteristics, like color, texture, structure, and mineral content. The depth of the soil also varies. The kind of soil in an area helps determines what type of plants can grow. There are 12 types: Alfisols, Aridisols, Entisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols, Gelisols, Andisols, and Vertisols.

Soil Formation Soil is formed slowly as rock erodes into tiny pieces near the Earth's surface. Organic matter decays and mixes with inorganic material (rock particles, minerals and water) to form soil.

Factors Affecting Soil Formation 1. Parent Material – this refers to the rock from which the soil develops. The mineral content in the parent material determines the nutrient richness of the resulting soil as well as the amount of soil produced.

Factors Affecting Soil Formation 2. Climate – soil formation is most rapid in warm, moist climates and slowest in cold, dry climates. 3. Topography – the physical landscape affects the rate of soil accumulation. Level areas will have more soil than steep slopes.

Factors Affecting Soil Formation 4. Time – generally, an older landscape should contain a more well-developed soil than a younger landscape. However, the other factors influence soil formation more strongly than time.

Soil Horizons Soil is made up of distinct horizontal layers. These layers are called horizons. They range from rich, organic upper layers to underlying rocky layers.

Soil Horizons

O Horizon - The top, organic layer of soil, made up mostly of leaf litter and humus (decomposed organic matter). A Horizon - The layer called topsoil; it is found below the O horizon and above the E horizon. Seeds germinate and plant roots grow in this dark-colored layer. It is made up of humus (decomposed organic matter) mixed with mineral particles. E Horizon - This eluviation (leaching) layer is light in color; this layer is beneath the A Horizon and above the B Horizon. It is made up mostly of sand and silt, having lost most of its minerals and clay as water drips through the soil (in the process of eluviation).

Soil Horizons B Horizon - Also called the subsoil; this layer is beneath the E Horizon and above the C Horizon. It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above. C Horizon - Also called regolith: the layer beneath the B Horizon and above the R Horizon. It consists of slightly broken-up bedrock. Plant roots do not penetrate into this layer; very little organic material is found in this layer. R Horizon - The unweathered rock (bedrock) layer that is beneath all the other layers.

Soil Uses Agriculture Mining Construction Waste management Water purification Food source (for some animals)