VII. GLOSSARY

Acre. Unit of measure of land equal to 43,560 square feet (for comparison, a football field is 48,000 square feet).

Aerobic. An organism or process that requires oxygen to live or function.

Aggregate, material. Gravel or crushed rock material, about 0.5 to 2.5 inches in diameter, used to distribute effluent in a trench or mound of an onsite wastewater disposal system.

Aggregate, soil. Many fine particles held in a single mass or cluster. Natural soil aggregates, such as granules, blocks or prisms, are called peds. Clods are aggregates produced by tillage or traffic on the soil.

Algae bloom. Abnormally rapid algae growth, often caused by high levels of nutrients and organic material.

Algae. Organisms that are single-celled, colonial, or multi-celled, and are usually aquatic and photosynthetic.

Alluvium. Material such as sand, silt, or clay deposited relatively recently by streams.

Aquifer. Porous layer of underground rock or rock material (sand) in which groundwater is held.

Available water capacity (available moisture capacity). Capacity of soils to hold water available for use by most plants. It is commonly defined as the difference between the amount of soil water at field moisture capacity and the amount at wilting point. It is expressed as inches of water per inch of soil.

Bacteria. Microscopic, one-celled organisms that lack chlorophyll and often derive nourishment from dead or decaying organic matter.

Bedrock. Solid rock that underlies the soil, sometimes many feet deep. It is sometimes exposed at the surface of the earth, especially in southern Indiana.

Biochemical oxygen demand (BOD). The requirement, or demand, for oxygen that organic and chemical matter places on water during the decomposition process.

Brittle. The term used to describe soil that ruptures suddenly or “pops” rather than deforms slowly when a small piece is pinched between thumb and forefinger.

Calcareous soil. Soil containing enough calcium carbonate (commonly with magnesium carbonate) to effervesce (fizz) visibly when treated with cold, dilute hydrochloric acid.

Capability subclasses. Noted by an e, w, or s following a soil’s capability class, for example IIe. The “e” indicates that the soil is erosive. A “w” signifies a wetness limitation. An “s” denotes a shallow, droughty, or stony soil.

Carbonate coats. A white or light gray calcareous covering on ped surfaces. Typically, carbonate coats are found only in dense till and have a dusty or grainy appearance. Carbonate coats fizz very rapidly if HCl is dripped on them.

Channers. Flat pieces of bedrock, up to six inches long.

Chisel tillage. Tillage with an implement having one or more soil-penetrating points that loosen the subsoil and bring clods to the surface.

Clay film. A thin coating of oriented clay on the surface of a soil aggregate or ped. Clay films are usually darker than the inside of peds and coat the peds like a coat of paint. They often have a somewhat shiny or waxy appearance. Synonyms are clay coat and clay skin.

Clay. As a soil separate, the mineral soil particles that are less than 0.002 millimeter in diameter. As a soil textural class, soil material that is 40% or more clay, less than 45% sand, and less than 40% silt.

Climate. The kind of weather that a region has over a period of years based on conditions of heat and cold, moisture and dryness, clearness and cloudiness, wind and calm.

Coarse fragments. Mineral or rock particles larger than 2 millimeters in diameter.

Coatings. Materials such as silt, clay, and/or carbonates that cover peds and/or pore surfaces. (see silt coat, carbonate coat, and clay film)

Colluvium. Loose material transported by surface runoff or slow continuous down slope creep that collects at the base of a slope.

Compaction, soil. The movement of soil particles closer together by external forces, such as falling rain, livestock traffic, or the weight of farm equipment. Compaction increases the bulk density and decreases the pore space between the particles of soil. With less pore space, the movement of water, air, and roots through the soil becomes more difficult and soil productivity decreases.

Conservation buffer. A permanent strip of grasses, shrubs, and/or trees designed to intercept nutrients and pollutants, slow water runoff, trap sediment, enhance water infiltration, and provide wildlife habitat.

Conservation tillage. Any tillage or planting system in which at least 30% of the soil surface is covered by plant residue after planting to reduce erosion. Examples of conservation tillage include practices such as strip-till, ridge-till, reduced or minimum till and no-till.

Conservation. Use of natural resources in a way to assure their continuing availability for future generations; the wise and intelligent use or protection of natural resources.

Contaminated/contamination. The addition of anything impure or unclean to something that was pure or clean.

Contour tillage. Tillage of soil along the contour of a hill (at the same elevation) rather than up and down a hill. It is a common practice used to reduce soil erosion in hilly terrain.Cover crop. A close-growing crop grown primarily to improve and protect the soil between periods of regular crop production, or a crop grown between trees and vines in orchards and vineyards.

Crop rotation. The practice of growing different crops in succession on the same land to help maintain healthy, productive soils.

Crop. Any plant product of cultivated agriculture, as distinguished from natural production or wild growth.

Decompose/Decomposition. Decay, rot, or breakdown by chemical change into simpler parts, accelerated by the presence of microorganisms consuming the material for their nutrients.

Degradation, soil. The usually irreversible deterioration of the soil, resulting in reduction of soil productivity. Erosion and soil compaction are major causes of soil degradation in Indiana.

Dense glacial till. Glacial till that was compressed or compacted due to the weight of glacial ice. It has a density greater than 1.75 g/cm3. (see glacial till)

Depression. Concave (shape of a bowl) area with a 2% or less slope in the midst of generally level land. A closed depression is bowl-shaped and has no outlet for water. An open depression is channel-shaped and water flows through it. (see swale)

Distribution box. A component of a septic system that accepts effluent from the septic tank and separates the flow evenly into a network of pipes in the soil absorption field. (see septic system, effluent, and soil absorption field).

Ditch drainage. Channels or open drains constructed for removing surplus water from land.

Dominant soil color. The most common or abundant color of the inside of a soil ped or aggregate.

Drainage. A natural or artificial system of water movement to or from a given site. (See natural soil drainage.)

Dune. A mound, ridge, or hill of loose wind-blown sand.

E. coli. (Escherechia coli). Bacteria commonly found in human and animal waste. Its presence is used as an indicator of poor water quality.

Effluent. Liquid materials resulting from sewage treatment. It usually contains small suspended solids as well as nutrients, pathogens, and contaminants.

Eolian material. Soil parent material accumulated through wind action; includes eolian sand (mainly in dunes) and loess.

Erosion. Wearing away of the land surface by running water or wind. Although erosion is a natural process, it is often accelerated above tolerable limits by man’s activities such as intensive farming and urban development.

Esker. A narrow, winding ridge of stratified gravelly and sandy outwash deposited by a stream flowing in a tunnel beneath a glacier.

Eutrophication. The overgrowth of aquatic vegetation followed by death, decay, oxygen depletion, and an imbalance of plants and animals in a lake or other body of water.

Evapotranspiration. The evaporation of water vapor by plants to the atmosphere.

Fertility, soil. The quality that enables a soil to provide plant nutrients, in adequate amounts and in proper balance, for the growth of specified plants when light, moisture, temperature, tilth and other growth factors are favorable.

Filter strips. A form of conservation buffer placed along drainage ways and streams. It is composed of grass and other vegetation and used to trap sediment, nutrients from manure and fertilizer, pesticides, and other pollutants so they do not enter the body of water.

Flood plain. Nearly level alluvial plain that borders a stream and is subject to flooding unless protected artificially.

Flooding. Temporary covering of soil with water from overflowing streams.

Foliated. Mineral aggregates that flake easily. Many metamorphic rocks are foliated.

Forage (crop). Grasses, alfalfa, etc. planted for food for domestic animals. Forage can be grazed by livestock or cut for hay.

Forest. Large dense growth of trees and other woody vegetation covering a large area.

Fragipan. Loamy, brittle subsurface horizon low in porosity and content of organic matter, and low or moderate in clay but high in silt. A fragipan appears cemented and restricts roots. When dry, it is hard or very hard and has a higher bulk density than the horizon or horizons above. When moist, it tends to rupture suddenly under pressure rather than to deform slowly.

Frost heave. Process of pushing something out of the soil caused by the expansion of water when it freezes. It can damage structures and plant roots.

Fungicide. Chemical used to kill fungi that are considered harmful to crops.

Glacial drift. General term for the sand, silt, and clay transported and deposited when a glacier melted. Glacial till (deposited directly from ice) and glacial outwash (deposited by the melt water of glacial ice) are specific examples of glacial drift.

Glacial till. (see till, glacial; compare to dense glacial till)

Glacier. A large, thick mass of ice that moves slowly due to its own weight. Glaciers that originated in Canada moved down into United States and covered most of Indiana thousands of years ago.

Granite. A common type of igneous rock composed of quartz, along with other minerals that are often pink, gray. and sometimes black.

Grassed waterway. Natural or constructed waterway, typically broad and shallow, seeded to grass as protection against erosion. Conducts surface water away from cropland.

Gravel. Rounded or angular fragments of rock up to 3 in. (2 millimeters to 7.5 centimeters) in diameter. An individual piece is a pebble.

Graze. To consume any kind of standing vegetation by domestic livestock.

Green manure. Soil-improving crop grown to be plowed under in an early stage of maturity or soon after maturity.

Groundwater. Water found in pores (spaces between particles) underground; the upper surface of groundwater is the water table. Groundwater is a source of drinking water for much of Indiana.

Growing season. Period of time when plants can grow and reproduce without frost damage.

Gully. Miniature valley with steep sides cut by running water and through which water ordinarily runs only after rainfall. The distinction between a gully and a rill is one of depth. A gully generally is an obstacle to farm machinery and is too deep to be eliminated by ordinary tillage; a rill is of lesser depth and can be smoothed over by ordinary tillage.

Habitat. Area that provides an animal or plant with adequate food, water, shelter, and living space in a suitable arrangement.

Harvest. To cut, reap, pick, combine, or gather any crop from the earth that is of value to people.

Herbicide. A chemical used to kill unwanted plants.

Hillslope. A landform component with 3% or greater slope.

Horizon, soil. Layer of soil, approximately parallel to the surface, having distinct characteristics produced by soil-forming processes. The major horizons of mineral soil are as follows:

O horizon. An organic layer consisting of fresh and decaying plant residue. On the surface of a mineral soil, it consists of leaves, needles, twigs, etc. In an organic soil, all horizons of the profile are O horizons.

A horizon. The surface mineral horizon in which organic matter has accumulated. It is generally darker than lower horizons. A and E horizons comprise the surface soil.

E horizon. The mineral horizon below the A horizon that is light in color and low in clay content, compared with underlying horizons. Percolating water removes, clay, iron, and aluminum from E horizons.

B horizon. The mineral horizon below an A or E horizon, also called subsoil. The B horizon has distinctive characteristics identified by 1) an accumulation of clay, iron, aluminum, silica, and/or humus; 2) prismatic or blocky structure; 3) redder or browner colors than those in the A horizon; or 4) a combination of these.

C horizon. The mineral horizon, excluding bedrock, that is little affected by soil-forming processes, also called substratum. The material of a C horizon may be either like or unlike that from which the A, E, or B horizons formed.

R horizon. Consolidated (hard) rock beneath the soil. The rock commonly underlies a C horizon, but can be directly below an A, E, or a B horizon.

Humus (humified). Well decomposed, more or less stable part of the organic matter in mineral soils.

Hydric soils. Wet soils classified on the basis of flooding, water table, and drainage class criteria. The definition was created for the implementation of legislation for preserving wetlands.

Hydrologic cycle. The continual movement of water over, in, and through the earth and its atmosphere as it changes from one form—solid, liquid, or vapor—to another.

Igneous rocks. Rocks formed from melted rock. Although Indiana has no bedrock that is igneous, igneous rocks were carried to the state thousands of years ago by glaciers that originated in Canada.

Impermeable (soil). Soil through which water, air or roots penetrate slowly or not at all. No soil is absolutely impermeable to air and water all the time.

Infiltration. Downward movement of water into the immediate soil surface; in contrast, “percolation,” is movement of water through soil layers or material.

Insecticide. Chemical used to kill unwanted insects.

Irrigation. Application of water to soils to assist in production of crops.

Kame. An irregular, cone-shaped hill of outwash.

Lacustrine deposit. Material deposited in lake water and exposed when the water level was lowered.

Lamellae. Thin bands of clay-enriched sandy soil material. For example, the Chelsea soil (Plate 7).

Land capability. Suitability classification of a land area for field crops or pasture that provides a general indication of the need for conservation treatment and management. Capability classes are designated by Roman numerals (I through VIII), which represent progressively greater limitations and narrower choices for practical land use. (see capability subclasses)

Land use. Utilization of an area of the earth’s surface, for farming, residential, or industrial purposes.

Landform component. A certain part of a landform such as hillslope, depression, or swell.

Landform. A physical feature on the earth’s surface that has a characteristic shape and was produced by natural causes. Examples of landforms include terrace, floodplain, and dune.

Leach/Leaching. Removal of materials such as nutrients or pollutants by water flowing down through the soil.

Lime. Crushed limestone, consisting largely of calcium carbonate (CaCO3) that reduces the acidity (raises the pH) of the soil and supplies it with calcium.

Limestone. A sedimentary rock consisting mainly of calcium carbonate (lime).

Loess. Material consisting mainly of silt-sized particles, deposited by wind.

Matrix. Soil material within peds or soil aggregates.

Metamorphic rocks. Rocks formed from previously existing rocks that have been buried and subjected to high temperatures and great pressure deep to the extent their chemical composition has been altered.

Microorganism. Living thing too small to be seen without a microscope. Synonym is microbe.

Mineral soil. Soil that is mainly mineral material rather than organic material. Its bulk density is greater than that of organic soil.

Mineral. Naturally occurring, inorganic material found in the Earth’s crust; they are nutritionally necessary for the proper growth and functioning of plants as well as humans.

Minimum tillage. The least tillage needed for crop production.

Moldboard plowing. A “clean tillage” practice that inverts the soil to a depth of 7 to 10 inches and buries the previous crop residue, leaving no cover to protect against erosion.

Moraine. Irregular hills of till deposited by a glacier.

Mottle. Irregular spot or patch of one color (the minor one) in a background of another color (the dominant or major one). Gray color, as the dominant color or mottles, generally indicates poor aeration and restricted drainage.

Muck. Dark colored, finely divided, well decomposed organic soil material mixed with mineral soil material. The content of organic matter is more than 20 percent.

Mulch. Protective covering such as crop residue, straw, manure, or other organic matter spread or left on the ground to prevent erosion, reduce evaporation, maintain even soil temperature, control weeds, and/or enrich the soil.

Munsell color notation. Designation of color by degrees of the three single variables—hue, value, and chroma. For example, a notation of 10 YR 6/4 is a color of 10 YR hue, value of 6, and chroma of 4. Determined using a color chart.

Natural soil drainage. Refers to the water regime of a soil through the year. Natural soil drainage classes are defined (in the Soil Survey Manual) according to how rapidly water is removed from the soil and how much internal free water there is in the soil (saturated horizons). Natural drainage classes are identified in the field, and in this book, by the amount of reduction features, or gray color in the soil profile. Gray color results from chemical reduction that occurs when a horizon is saturated (below the water table).

Excessively drained. (Included with well drained for soil evaluation.) Water is removed very rapidly. Soils are usually very coarse textured (sandy and gravelly). They have no reduction features.

Somewhat excessively drained. (Included with well drained for soil evaluation.) Water is removed rapidly. Soils are usually coarse textured (sandy and gravelly). They have no reduction features.

Well drained. Water is removed from the soil readily but not rapidly. Soils may have reduction features below 30 inches, but may be occasionally saturated at shallower depths.

Moderately well drained. Water is removed from the soil somewhat slowly during some periods. Soils have reduction features between 18 and 30 inches and are periodically saturated in that zone.

Somewhat poorly drained. Water is removed slowly enough that the soil is wet for significant periods during the growing season. Soils have reduction features above 18 inches and are occasionally saturated almost to the surface.

Poorly drained. Water is removed so slowly that the soil is wet at shallow depths periodically during the growing season or remains wet for long periods. Free water is commonly at or near the surface for long enough during the growing season that most common crops cannot be grown routinely unless the soil is artificially drained. Reduction features are in the surface horizon or directly below it.

Very poorly drained. (Included with poorly drained for soil evaluation.) Unless artificially drained, water is frequently ponded on the soil surface and the entire soil remains wet for long periods. Usually the soil surface is black and deep, and reduction features are immediately below this dark layer.

Nitrate (NO3). Nitrogen in a form that is available to plants. It forms naturally in the atmosphere during electrical storms and is manufactured as fertilizer. Too much nitrate, however, can leach into the groundwater or runoff into rivers and steams and can contaminate drinking water.

Nitrogen (N). Gaseous element occurring in the atmosphere. It occurs naturally in soil and is an essential plant nutrient.

Non-point source pollution. Pollution and contaminants that enter streams from broad areas of land such as farms, parking lots, and residential areas. The greatest source of non-point source pollution is sediment due to soil erosion.

No-till planting. A crop (such as corn) is planted directly in soil that has a residue from a previous crop (e.g., soybean) without any sort of tillage plowing (or disking) of the soil.

Nutrient, plant. Any of the elements taken in by a plant, essential to its growth, and used by it in the production of food and tissue.

Organic material. Very dark to black soil component that formed from partially decomposed vegetation and animal residue.

Outwash plain. A large, mostly level area not confined in a river valley that is composed of outwash material (sand and gravel).

Outwash, glacial. Stratified sand and gravel produced by glaciers and carried, sorted, and deposited by water that originated mainly from the melting of glacial ice. Glacial outwash is commonly in terraces, eskers, kames, or outwash plains.

Overwash. Material washed into depressions from nearby higher areas.

Parallel tile outlet (PTO). Terraces that are constructed parallel to one another and that use a surface inlet riser to discharge surface water runoff through subsurface drains and tiles to a ditch or other appropriate outlet.

Parent material. The great variety of unconsolidated organic and mineral material in which soil forms. Consolidated bedrock is not yet parent material by this concept.

Pasture. A field of perennial vegetation (lasts for many years) that is used for grazing livestock.

Pathogen. Disease causing organism.

Peat. Unconsolidated organic material, largely undecomposed, that has accumulated under excess moisture.

Ped. Individual natural soil aggregate, such as a granule, prism, or block.

Percolate/percolation. Downward movement of water through the soil.

Permeable/permeability. The quality that enables the soil to transmit water or air. Slow or low permeability means that water and air move very slowly through the soil. It is expressed as a rate (inches of water per hour).

Pest management. Ecological approach to reducing damage by pests through use of the most economical means with the least possible hazard to people and the environment. This includes surveying pest populations, introducing natural enemies of pests, and carefully timed and confined spraying of chemicals.

Pesticide. A chemical used to kill insects, fungi, plants, or animals that are considered to be pests.

pH. The scale used to determine the acidity or alkalinity of a substance based on its hydrogen ion content. The scale ranges from 0 to 14, with 7 being neutral. The zero end is most acidic, while the 14 end is most alkaline.

Phosphorus (P). An essential nutrient needed for plant growth. In normal concentrations, P is held tightly by soil particles. If too much phosphorus is applied to the soil, however, and excess P may be carried into ditches, streams, or other bodies of water, where it causes algal blooms (smelly green pond scum). (see eutrophication)

Photosynthesis. The manufacture of carbohydrate from carbon dioxide and water. The process uses energy from the sun and releases oxygen.

Plain. A land surface that is flat to gently sloping in overview but may be rolling on closer examination. Examples include till plains, outwash plains, and floodplains.

Plow. To cut through and turn over a layer of topsoil.

Plowpan. Compacted layer formed in the soil directly below the plowed layer.

Point rows. A partial row of crop that does not continue the entire length of the field due to irregular field borders or an obstruction such as a wetland.

Point source pollution. Pollution or contaminants that enter a body of water from a specific point. Examples are municipal sewage treatment plants and industrial discharges into streams.

Ponding. Standing water on soils in closed depressions. Unless the soils are artificially drained, the water can be removed only by moving down through the soil or evapotranspiration.

Pores. Small, sometimes microscopic passages in rock and soil that allow the passage of fluids and air.

Potassium (K). A very important plant nutrient that increases both yield and quality of crops. Because it doesn’t move readily in the soil, it is not as environmentally damaging as the other two nutrients commonly in fertilizer (N and P).

Prime farmland. Soils that have the best combination of physical and chemical characteristics for producing food, feed, forage, fiber, and other crops.

Productivity, soil. Capability of a soil for producing a specified plant or sequence of plants under a specified system of management. Productivity is measured in terms of output, or harvest, in relation to input.

Profile, soil. Vertical section of the soil extending through all its horizons and into the parent material; in three dimensions, it is called a pedon.

Quartz. A mineral composed of silicon and oxygen (SiO2). It is one of the most common minerals in the igneous rock called granite. Most sand grains in soils are quartz.

Recharge (of groundwater). The process by which water —from rainfall, snowmelt, and other sources —flows into a water-bearing geologic formation (aquifer).

Relief. The difference in elevation between the highest and lowest points n the landscape.

Residue, crop. Part of a plant left in the field after harvest. The practice of leaving crop residue is encouraged because it provides a covering for the soil to protect it against erosion.

Residuum (residual soil material). Unconsolidated, weathered, or partly weathered mineral material that accumulates over disintegrating rock.

Respiration. The exchange of gases in order to obtain the compounds required for energy; specifically, the use of oxygen which organisms use to break down food (carbohydrates) into energy plus carbon dioxide and water.

Ridge-till planting. At planting time, ridge scrapers push some soil and the dead residue left from the previous crop off the top of ridges. Seed is then planted on the top of the residue-free ridge, and the crop residue accumulates in the area between the ridges to help reduce erosion and control weeds. Ridges are rebuilt when the crop is cultivated for weed control.

Rill. A steep-sided channel resulting from accelerated erosion. A rill is generally a few inches deep and not wide enough to be an obstacle to farm machinery.

Rock fragments. Rock or mineral fragments having a diameter of 2 millimeters or more; for example, pebbles (gravel) cobbles, stones, channers, flags, and boulders.

Root zone. The part of the soil that can be penetrated by plant roots.

Row crops. Crops such as corn and soybeans that are planted in rows more than about 15 inches apart so that equipment to control weeds, apply chemicals, and harvest crops can be driven through the field without running over plants.

Runoff. The movement of water across a surface to a stream or other body of water.

Sand filter. A secondary wastewater treatment system consisting of a bed of sand through which septic tank effluent passes in the presence of air and is further purified before it is passes to the soil absorption field.

Sand. As a soil separate, individual rock or mineral fragments from 0.05 millimeter to 2.0 millimeters in diameter. Most sand grains consist of quartz. As a soil textural class, a soil that is 85% or more sand and not more than 10% clay.

Sandstone. Sedimentary rock containing dominantly sand-size particles.

Saturated zone. The area of the zone where the pores are completely filled with water. The water table is at the top of the saturated zone. (see water table)

Sediment. The material suspended in or carried by wind or water that settles when, that which carries it, becomes calmer.

Sedimentary rock. Rock made up of particles deposited in water and cemented together. The chief kinds are sandstone (formed from sand), siltstone (formed from silt), shale (formed from clay), and limestone (formed from the calcium carbonate in marine animal shells).

Seepage. Movement of water through the soil.

Septic system. Wastewater treatment systems that use a septic tank and soil to treat small wastewater flows, usually from individual homes. They are typically used in rural or large lot settings where centralized wastewater treatment is impractical. An onsite wastewater disposal system consists of a septic tank, a distribution box, and a drain field or soil absorption field.

Septic tank. An underground tank usually made of concrete that temporarily holds wastewater from a household so that heavy solids and lighter scum are allowed to separate from the wastewater. The solids stored in the tank are decomposed by bacteria, and the remnants are later removed, along with the lighter scum, by a professional septic tank pumper. (see septic system)

Series, soil. A group of soils, formed from a particular type of parent material, having horizons that, except for the texture of the A or surface horizon, are similar in all profile characteristics and arrangement in the soil profile. Among these characteristics are color, texture, structure, reaction, consistence, and mineralogical and chemical composition.

Shale. Sedimentary rock formed by the hardening of a clay deposit.

Sheet erosion. Removal of a fairly uniform layer of soil material from the land surface by the action of rainfall and runoff water; does not follow a channel.

Shrink-swell. Shrinking of soil when dry and swelling when wet. Shrinking and swelling can damage roads, dams, building foundations, and other structures. It can also damage plant roots.

Silt coat. Coatings of silt grains on ped surfaces. Silt coats appear to be dusty and powdery, like sugar on a donut. Thin silt coats can be distinguished from clay skins by moistening the sample. If the coating is silty, the color of the coating disappears and the underlying color of the ped comes through. A clay film will keep its color when moist. Silt coats are NOT an indicator of natural drainage, whereas the presence of gray clay coats or films can be.

Silt. As a soil separate, individual mineral particles that range in diameter from the upper limit of clay (0.002 millimeter) to the lower limit of very fine sand (0.05 millimeter). As a soil textural class, soil that is 80% or more silt and less than 12% clay.

Siltstone. Sedimentary rock made up of dominantly silt-sized particles.

Sinkhole. A closed depression (has no outlet for water to escape) that formed by dissolution of limestone.

Slope. Inclination of the land surface from the horizontal. Percentage of slope is the vertical distance divided by horizontal distance, then multiplied by 100. Thus, a slope of 20% is a drop of 20 ft. in 100 ft. of horizontal distance.

Small grains. Crops such as wheat, barley, oats, and rye that are usually seeded in narrow rows (less than 10 inches apart). These crops produce most of their growth during cool seasons (late fall to early winter).

Soil absorption field. A system of drain lines through which effluent moves to the soil where it is further purified by soil microbes. Located in an unsaturated zone of the soil, the absorption field contains perforated pipes that allow wastewater to trickle into the soil. The soil acts as a natural buffer to filter out many of the harmful bacteria, viruses, and excessive nutrients after it leaves the septic tank and before it enters the groundwater. (Synonyms: septic absorption field, drain field)

Soil conservation. Practices to maintain healthy soil by minimizing soil erosion, soil nutrient depletion, and soil compaction. (see conservation buffer, conservation tillage, contour tillage, filter strips, no-till planting, PTO, WASCOBs)

Soil survey. An inventory of soil resources. It consists of soil maps, technical information about soils, and information about using soils. Soil surveys are usually published by counties.

Soil. A natural, three-dimensional body at the earth’s surface that is capable of supporting plants and has properties resulting from the integrated effect of climate and living matter acting on earthy parent material, as conditioned by relief over periods of time.

Solum. Upper part of a soil profile, above the C horizon, in which the processes of soil formation are active. The solum in mature soil consists of the A, E, and/or B horizons. Generally, the characteristics of the material in these horizons are unlike those of the underlying material. Living roots and other plant and animal life in the soil are largely confined to the solum.

Splash erosion. The particles of soil that are loosened and thrown into the air by raindrops that strike the earth with considerable speed and energy.

Stratified. Deposited in strata, or layers.

Strip cropping. Growing crops in a systematic arrangement of strips or bands which provide vegetative barriers to wind and water erosion.

Strip-till planting. Planting seeds such as corn or soybeans in a narrow strip that has been cleared of plant residue and tilled. Much like no-till planting, except that residue from a previous crop is cleared from a narrow strip in which seeds are planted.

Structure, soil. The grouping of individual soil particles or aggregates into units called peds. The principal forms of soil structure are platy (laminated), prismatic (vertical axis of aggregates longer than horizontal), columnar (prisms with rounded tops), blocky (angular or subangular) and granular.

Subsoil. Technically, the B horizon; roughly, the part of the solum below plow depth.

Subsoiling. Tilling a soil below normal depth, ordinarily to shatter a tillage pan.

Substratum. The part of the soil below the solum (C horizon) that lacks development.

Subsurface drainage. Underground drainage system that removes subsurface water though a series of clay or concrete tiles or perforated plastic tubing installed at a slight grade to facilitate flow to an outlet.

Surface drainage. a.) The natural pattern by which water moves across the soil surface as overland flow. b.) A man-made system of grading the soil to enhance overland flow.

Surface inlet riser. A pipe intake that extends above the ground and directs surface or ponded water into an underground tile or outlet. (see parallel outlet terraces)

Surface soil. The soil ordinarily moved in tillage, or its equivalent in uncultivated soil, ranging in depth from 4 to 10 in. Frequently designated as “plow layer,” “topsoil,” or “Ap horizon.”

Surface water. Any body of water on the earth’s surface such as lakes, rivers, and creeks. It also includes water in drainage ditches and water that seeps from a hillside. Surface water is the source of drinking water for many cities.

Swale. Concave (the shape of a bowl) landform with a 2% or less slope. (see depression)

Swell. Convex (shape of a ball) landform with a 2% or less slope.

Swell-and-depression topography. Composed of both swells (small rises) and depressions (small indents), which results in “rolling” scenery.

Terrace (geologic). An old alluvial plain, ordinarily flat or undulating, bordering a river, a lake, or the sea. A stream terrace is seldom subject to overflow.

Terrace (structure). Embankment or ridge constructed across sloping soils on the contour or at a slight angle to the contour. The terrace intercepts surface runoff so that it can soak into the soil or flow slowly to a prepared outlet without harm. A terrace in a field is generally built so that the field can be farmed.

Texture, soil. The relative proportions of sand, silt, and clay particles in a mass of soil.

Texture group. Five groups are used in soil evaluation. Each group is comprised of one or more soil texture classes as listed below:

Sandy. Sand and loamy sand texture classes.

Moderately sandy. Sandy loam texture classes.

Medium. Loam, silt loam, and silt texture classes.

Moderately clayey. Sandy clay loam, clay loam, and silty clay loam texture classes.

Clayey. Sandy clay, silty clay and clay texture classes.

Tile drainage. Underground drainage system composed of clay or concrete tiles or perforated plastic tubing installed at a slight grade to facilitate the flow of subsurface water to an appropriate outlet. (Synonym: subsurface drainage)

Till plain. An extensive flat to undulating landform underlain by glacial till.

Till, glacial. Unsorted, non-stratified (not layered) material transported and deposited by glacial ice. It consists of a mixture of clay, silt, sand, pebbles, and boulders in various proportions.

Tillage. Preparation of the land for planting. Traditionally this was done by moldboard plowing and disc harrowing. Conservation tillage (ridge-till, minimum till, no-till, etc.) is now the preferred method so as to control erosion. (see conservation tillage)

Tolerable soil loss (T). The amount of soil that can be eroded without causing long-term harm to farming productivity. In Indiana, the tolerable soil loss for most soils is two to five tons per acre per year.

Topography. The detailed physical features of an area, such as plains, hills, and other land features.

Topsoil. The upper part of the soil, which is the most favorable material for plant growth. It is ordinarily rich in organic matter.

Unsaturated zone. The area of the soil where pores are filled partly with air and partly with water. This is the area above the water table and is important to the purity of the groundwater underlying it. (see water table and groundwater).

Upland. Land at a higher elevation, in general, than the alluvial plain or stream terrace; land above the lowlands along streams.

Wastewater disposal systems. Wastewater treatment systems that use the soil to treat small wastewater flows, usually from individual homes. They are typically used in rural or large lot settings where centralized wastewater treatment is impractical. A wastewater disposal system consists of a septic tank, a distribution box, and a drain field or soil absorption field. Synonym: septic system.

Wastewater. The used water that exits our homes and industries. Although it is mostly water by weight, it often contains components that have the potential to cause disease or detrimental environmental effects. The waste may include solids from human excrement, pathogens, organic matter, oil and grease, and nutrients. (see wastewater disposal systems)

Water and sediment control basins (WASCOBs). Shorter versions of parallel tile outlet terraces that are built only across the natural drainage ways in the field rather than the entire field. They are constructed mainly to control gully erosion. (see parallel tile outlet)

Water table. Upper limit of the soil or underlying rock material that is completely saturated with water. The boundary between the unsaturated and saturated zone of the soil.

Weathered bedrock. Bedrock that is broken down by physical and/or chemical processes. Although it is still rock, it is soft enough that roots can grow into it.

Weathering. All physical and chemical changes produced in rocks or other deposits at or near the earth’s surface by atmospheric agents. These changes result in disintegration and decomposition of the material.

Wetlands. Areas of hydric soil that are saturated with water at or very near the surface for at least several weeks during the growing season and support water-loving plants such as cattails and reeds. Sometimes wetlands are “constructed” specifically to purify effluent from a septic tank, using the same principal as a natural wetland with plants and microbes to purify the water that flows into it.

Windbreak. A conservation buffer composed of trees and shrubs used to reduce wind erosion, protect young crops, and control blowing snow.