A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. A soil horizon makes up a distinct layer of soil. Decomposition occurs very quickly, but the nutrients recycled into the soil are rapidly pulled back out by other vegetation. Gases found in soil profiles are said to form the soil atmosphere which is one of the most important components of the soil. Soil Soil is the thin top layer on the earth’s crust comprising rock particles mixed with organic matter. The soil profile extends from the soil surface to the parent rock material. For example, a sandy loam soil with 20% gravel would be called gravelly sandy loam. Soil Changes with Age - As a soil ages, it gradually starts to look different from its parent material. Soils: Components and basic chemistry Justin Scheiner, Ph.D. Assistant Professor and Extension Viticulture Specialist Components of Soil Minerals: decomposition of rock Organic matter: decomposed plants, animals, & microbes Water: atmosphere & soil reactions Air: atmosphere ≥48% 25% 25% ≤2% The traditional definition is: Soil is a dynamic natural body having properties derived from the combined effects of climate and biotic activities, as modified by topography, acting on parent materials over time. Put the horizons together, and they form a soil profile. A soil is simply a porous medium consisting of minerals, water, gases, organic matter, and microorganisms. Its components—minerals, water, air, … The soil profile is defined as a vertical section of the soil from the ground surface downwards to where the soil meets the underlying rock. Put the horizons together, and they form a soil profile. That’s because soil is dynamic. Like a biography, each profile tells a story about the life of a soil. These are filled with moisture and air in varying quantities which account for approximately half of the total volume of soil. Soil profile classes were defined at various levels of generalization (e.g., series, family, great soil group or phase), depending on the information available, purpose of survey, and scale of mapping. Pedology is the study of soils in their natural environment. The soil profile can be as little as 10 cm thick in immature soils and as deep as several metres in tropical areas where the climate is conducive to rapid alteration of the underlying rock to form soil. The soil is the topmost layer of the earth’s crust mainly composed of organic minerals and rock particles that support life.