It contains mineral material derived from the parent material and organic matter derived from living plants and other organisms in the soil. The major soil-forming factors are parent material, climate, vegetation, and time. Soil colloids are the smallest particles in soils. They are important because they hold plant nutrients in the soil in the form of ions. Soil pH can range from acid to alkaline.
Soil structure refers to the way in which the soil grains are bound together by colloids into peds.
Chemical and organic processes in soils change primary minerals into secondary minerals such as oxides and clay minerals. The nature of the clay minerals determines a soil's base status which, in turn, affects its fertility or ability to retain nutrients. The storage capacity of a soil is the maximum amount of water that it can retain by capillary tension when it is allowed to drain. Water stored within a soil is depleted by evaporation and transpiration until it is recharged by precipitation. A soil water budget is a numerical accounting, usually done on a monthly basis, of the soil water balance components.