Soil Terminology
Need a good overview of soil monitoring related words and phrases? Read on for definitions of common words used in the industry. Have a suggestion? Submit it!
A
A: Name of a soil horizon. Horizon "A" is a top soil rich in organic matter. Typically found 2 to 10 inches below the surface.
Alfisols: One of the 12 orders of soil. Alfisols are in semiarid to moist areas. They formed under forest or mixed vegetative cover and are productive for most crops.
Allowable Depletion: Represents the amount of soil moisture that can be removed by the crop from the soil before the crop begins to stress.
Andisols: One of the 12 orders of soil. Andisols tend to be highly productive soils. They are common in cool areas with moderate to high precipitation, especially those areas associated with volcanic materials.
Aridisols: One of the 12 orders of soil. Aridisols are soils that are too dry for the growth of mesophytic plants. They often accumulate gypsum, salt, calcium carbonate, and other materials that are easily leached from soil in more humid environments. Aridisols are common in the world's deserts.
Available Water Capacity (AWC): The amount of water in the soil that is available to the plant.
B
B: Name of a soil horizon. Horizon "B" is a subsoil, the most diverse horizon and the horizon with the most sub classifications. Typically found 10 to 30 inches below the surface.
C
C: Name of a soil horizon. Horizon "C" is made up of weathered/aged parent material and can usually be found 30 to 48 inches below the surface.
Carbon Dioxide (CO2): Carbon Dioxide is a gas that is found naturally in the atmosphere, in the human blood stream and is used by plants as part of photosynthesis. However, because of its ability to absorb light and stay in the atmosphere for extended periods of time it has been thought that CO2 may be one factor in global warming.
Carbon Sink: A carbon sink is anything that is collecting more CO2 from the atmosphere than it's releasing. Major carbon sinks include the world's oceans and young plants and forests. Carbon sequestering can be used to further enhance the ability of these sinks to capture carbon from the atmosphere.
D
Dioxane (1,4-dioxane): This clear organic, carcinogenic compound is oftentimes used as a solvent in manufacturing processes. It has been found in contaminated groundwater.
E
E: Name of a soil horizon. Horizon "E" has been leached of organic or mineral content and is light in color.
Electrical Conductivity (EC): Measured in Siemens per meter, soil electrical conductivity is indicative of dissolved salts, dissolved solids, and fertilizers. It may also be indicative of very high pH conditions.
Entisols: One of the 12 orders of soil. Entisols occur in areas of recently deposited parent materials or in areas where erosion or deposition rates are faster than the rate of soil development; such as dunes, steep slopes and flood planes.
F
Field Capacity: refers to the amount of water left behind in soil after gravity drains saturated soil.
G
Gelisols: One of the 12 orders of soil. Gelisols are soils that have permafrost near the soil surface, have evidence of frost churning, or ice segregation. These are common in the higher latitudes or high elevations.
H
Histosols: One of the 12 orders of soil. Histosols have a high content of organic matter and no permafrost. Most are saturated year round, but a few are freely drained. They are commonly called bogs, moors, pears or mucks.
Horizon: Soil horizons are distinct layers of soil that form naturally in undisturbed soil over time. The types of horizons are indicative of the soil order. Like other natural processes, the age of the horizon increases with depth.
I
Inceptisols: One of the 12 orders of soil. Inceptisols are soils of semiarid to humid environments that generally exhibit only moderate degrees of soil weathering and development. These occur in a wide variety of climates.
J
K
L
Lower soil moisture Limit: The soil moisture value below which the crop will become stressed because it will have insufficient water. When the lower limit is reached, it is time to irrigate.
M
Maximum Allowable Depletion (MAD): The fraction of the available water that is 100% available to the crop.
Mollisols: One of the 12 orders of soil. Mollisols are soils that have a dark colored surface horizon relatively high in content of organic matter. The soils are base rich throughout and therefore are quite fertile.
N
Nitrogen: A chemical compound that can be found in all living organisms, the atmosphere, and animal wastes. It is commonly found in nutrients used in fertilization, and can cause problems to local ecosystems if too much is washed into waterways.
O
O: Name of a soil horizon. Horizon "O" is made up of decaying plants on or near surface and is typically up to 2 inches thick.
Oxisols: One of the 12 orders of soil. Oxisols are highly weathered soils of tropical and subtropical regions. They characteristically occur on land surfaces that have been stable for a long time. They have low natural fertility as well as a low capacity to retain additions of lime and fertilizer.
P
Perchloroethylene (PCE): See Tetrachloroethylene (TCE).
Permanent Wilting Point: Refers to the amount of water in soil that is unavailable to the plant.
Phosphorus: A highly reactive chemical element used in fertilizers to aid in plant growth. Phosphorus can cause oxygen problems and unwanted algae blooms if too much is washed into bodies of water, creating hardship for the local ecosystem.
Phytoremediation: A remediation method by which trees are used to pull contamination out of groundwater. When the trees absorb the water and then off-gas it during photosynthesis, the toxic chemicals are rendered into relatively harmless by-products such as methane and carbon dioxide.
Probe: The end of a soil probe that is buried or otherwise sunk into the ground in order to take measurement readings of the surrounding soil. The name "soil probe" is also used as a general name for any number of devices designed to measure soil, and is also interchangeably referred to as a "soil sensor".
Q
R
S
Sensor: "Soil Sensor" is used to describe a device that measures soil parameters such as temperature and soil moisture content. Also know as a "soil probe", these names can be used interchangeably.
Soil Carbon Flux: Also known as soil respiration, this is the result of bacteria and other microorganisms in the soil consuming organic material or decaying plant matter, which in turn produces CO2 that is off-gassed into the atmosphere and groundwater.
Soil Saturation: Refers to the situation where all the soil pores are filled with water. This occurs below the water table and in the unsaturated zone above the water table after a heavy rain or irrigation event. After the rain event, the soil moisture (above the water table) will decrease from saturation to field capacity.
Spodosols: One of the 12 orders of soil. Spodosols formed from weathering processes that strip organic matter combined with aluminum from the surface layer and deposit them in the subsoil. These tend to be acid and infertile.
T
Tetrachloroethylene (TCE): A chemical that is used in the dry-cleaning industry. It has been found in contaminated groundwater and is toxic in low levels and has been linked with cancer in humans.
U
Ultisols: One of the 12 orders of soil. Ultisols are soils in humid areas. They are typically acid soils in which most nutrients are concentrated in the upper few inches. They have a moderately low capacity to retain additions of lime and fertilizer.
V
Vertisols: One of the 12 orders of soil. Vertisols have a high content of expanding clay minerals. They undergo pronounced changes in volume with changes in moisture. Because they swell when wet, vertisols transmit water very slowly and have undergone little leeching. They tend to be fairly high in natural fertility.
W
Water Fraction by Volume (WFV): This term describes the percentage of water found in the soil displayed in decimal form. For example, a water content of 0.20 wfv means that a one liter soil sample contains 200 ml of water. Full saturation (all the soil pore spaces filled with water) occurs typically between 0.3-0.45 wfv and is quite soil dependent. WFV is a desirable way to measure water content of soils because you can compare the content directly between different types of soil with no conversion between units.
