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The Soil System
| Term | Definition |
|---|---|
| Soil | the uppermost layer of earth's crust; supports terrestrial plants, animals, and microorganisms. |
| State Factors | determine the state of the soil system. the 5 main ones are parent material, climate, topography, organisms, and time. |
| Weathering Processes | a biological, chemical, or physical process that helps form soil from rock; rock is gradually broken down into smaller and smaller particles. |
| Parent Material | rock that is slowly broken down, or fragmented, into smaller and smaller particles by biological, chemical, and physical weathering processes in nature. |
| Topography | a region's surface features. if a region has a steep slope, there is little to no soil because of erosion (precipitation) and gravity. as for moderate slopes and valleys, deep soil formation is encouraged. |
| Humus | the black/dark-brown organic material that reminds after much decomposition has occurred. it is not a single chemical compound but a mix of many organic compounds. it also binds to nutrient material ions and holds water. |
| Soil Horizons | the horizontal layers into which many soils are organized, from the surface to the underlying material. |
| Soil Profile | a vertical section from the surface to parent material, showing the soil horizons. |
| O Horizon | a horizon that is rich in organic material. plant litter accumulates and gradually decays. |
| A Horizon | a horizon known as top soil. this layer is dark and rich in accumulated organic matter and humus. it is somewhat nutrient-poor because of the gradual loss of many nutrient minerals to deeper layers by leaching. |
| B Horizon | a horizon known as subsoil. this lighter-colored layer is rich in iron and aluminum compounds and clay. plant roots penetrate this area, but there is less humus and more inorganic content. |
| C Horizon | a horizon which contains weathered pieces of rock and borders the parent material. it is below the extent of most roots and if often saturated with groundwater. |
| Ecosystem Services | important environmental benefits that ecosystems provide to people; include clear air to breathe, clean water to drink, and fertile soil in which to grow crops. |
| Castings | bits of soil that have passed through the gut of an earth-worm. they are deposited on the soil surface, bringing nutrient minerals from deeper layers in the soil to the upper layers. |
| Mycorrhizae | an important symbiotic relationship in the soil that occurs between fungi and the roots of vascular plants. it helps plants absorb adequate amounts of essential nutrient minerals from the soil. |
| Mycelium | the threadlike body of the fungal partner which extends into the soil well beyond the roots. |
| Nutrient Cycling | the pathway of various nutrient minerals or elements from the environment through organisms and back to the environment. |
| Soil Texture | the relative proportions of different-sized inorganic mineral particles of sand, silt, and clay. |
| Sand | has the largest soil particles; are large enough to be seen easily with the eye. |
| Silt | has the medium-sized soil particles; are about the size of flour particles and are barely visible to the eye. |
| Clay | has the smallest soil particles; are only seen under an electron microscope. |
| Loam | an ideal agricultural soil; has an optimum combination of different soil particle sizes. 40% of sand and silt, 20% clay. |
| Soil Acidity | measured using the pH scale. a soil's pH affects plants partly because soil nutrients are either available or unavailable depending on the pH |
| Acid Precipitation | a type of air pollution in which human-produced sulfuric and nitric acids falls to the ground as acid rain, acid sheet, acid snow, or acid fog. it alters soil chemistry, damages plants, and causes forest decline in some areas. |
| Soil Taxonomy | the method of classification of these soils into 12 distinctive orders; each order is subdivided into many different series. |
| Spodosols | this type of soil is located in regions with cooler climates, ample precipitation, and good drainage. they have distinct layers and form under a coniferous forest. |
| Alfisols | this type of soil is located in temperate deciduous forests. it has a brown to gray-brown A horizon. |
| Mollisols | this type of soil is located in primarily in temperate, semiarid grasslands. they are fertile soils and possess a thick, dark-brown to black A horizon rich in humus. most of the world's crops are grown here. |
| Aridisols | this type of soil is located in arid regions of all continents. they do not have distinct layers of leaching and illuviation. these soils may provide rangeland for grazing animals, while crops can be grown if water is supplied by irrigation. |
| Oxisols | this type of soil is located in tropical and subtropical areas with ample precipitation. they are low in nutrient minerals, and only little organic material accumulates on the forest floor due to leaves and twigs decomposing. |
| Sustainable Soil Use | the wise use of soil resources, without a reduction in soil fertility, so that the soil remains productive for future generations. |
| Soil Erosion | the wearing away or removal of soil, especially topsoil, from the land. water, wind, ice, and other agents promote this action. |
| Salinization | the gradual accumulation of salt in a soil, often as a result of improper irrigation methods. |
| Desertification | degradation of once-fertile rangeland, agricultural land, or tropical dry forest into nonproductive desert. |
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