Factors of Soil Development Parent material Climate Topography Organisms Time

Parent Material The sediments or rock in which the soil develops Influence Soil texture sandy sediments become sandy soils Soil chemistry mafic rocks become soils with higher levels of mineral nutrients

Climate The long-term conditions of temperature and precipitation Influence The degree of soil development Warmer conditions enhance soil development Wetter conditions enhance soil development Chemical weathering and other chemical reactions The vegetation that grows in the soil

Topography Slope steepness, slope orientation, and landscape position Affects the separation of rainfall into infiltration and runoff Steeper slopes have less infiltration and more runoff Less infiltration means less soil development More runoff means more surface erosion which slows down soil development

Topography Slope orientation Landscape position Affects the amount of sunlight received South-facing slopes are warmer which enhances soil development Landscape position Affects the internal drainage of the soil Higher landscape positions have better drainage which enhances soil development

Organisms The plants and animals that live in the soil. Influence Nutrient levels in the soil Deciduous trees take up lots of nutrients which are then returned to the soil when leaves fall and decay Coniferous trees do not take up many nutrients allowing those in the soil to be leached away The structure (openness) of the soil Allows better movement of air and water through the soil

Time The length of time that soil-forming processes have been acting at a specific location The longer the time, the greater the degree of soil development Because soils develop from the surface downward Erosion of surface horizons sets back the clock of soil development

How Do Soils Develop? From the ground surface downward… Forming layers called soil horizons… Through the Addition Transformation Removal of material to, within, or from a horizon. http://courses.soil.ncsu.edu/resources/soil_classification_genesis/soil_formation/soil_transform.swf

The Soil Horizons O horizon A horizon E horizon B horizon C horizon Dead and decaying organic matter A horizon Mix of organic and mineral matter – “topsoil” Zone of removal E horizon Zone of extreme removal B horizon Clay-rich – “subsoil” Zone of accumulation C horizon Weathered bedrock or minimally altered sediment R horizon Unweathered bedrock

Soil Profiles and Soil Series The sequence of soil horizons present at a specific location Defined by the type and thickness of horizons present Soil Series A named soil profile used for soil mapping Soil Series are typically grouped together in Soil Associations