Soil

Soil is a combination of broken down rock and decomposed organic materials. Geologists study the soil profile, which is a cross section of the soil from the surface down to the bedrock. The soil profile is divided into layers called horizons.

Soil is classified according to climate, plant vegetation and soil composition. Different types of soil are found in different climate biomes. Plant vegetation impacts the amount of organic material called humus that is found in the topsoil.

Tropical climates with lush vegetation often have a thin layer of topsoil because high rainfall washes away humus and minerals in the A horizon. Soil layers are also thin in harsh climates such as deserts and arctic regions.

Temperate climates have the most nutrient-rich, productive soils. Moderate rainfall results in abundant plant life, and the soil profile has a thick layer of topsoil with humus.

Many organisms live in the soil and contribute to its formation. Burrowing animals help create the soil profile by breaking up rock and other materials. Worms, fungi and bacteria decompose decaying matter.

Soil is a non-renewable resource that can be easily depleted or destroyed. Removal of cover crops like grasses and wildflowers leads to rapid soil erosion. Without cover plants, wind can blow away topsoil in clouds of dust, and significant flooding can occur.

Many modern farmers use techniques to conserve soil. Crop rotation prevents depletion of soil nutrients. Low-till plowing minimizes soil disturbance, and contour plowing reduces the erosion of topsoil from water runoff.