Plymouth County Soil Survey
Description of Soil Properties Table
The following are explanations of soil properties found in the map unit descriptions. For more information on soil properties contact the Plymouth County Soil Survey Office.
Can't find it? Click here for soil glossary of soil terms.
Complete descriptions are found here: National Soil Survey Handbook.
|Map Unit||Parent Material||Available Water Holding Capacity||Seasonal high water table|
|Map Unit Phases||Drainage Class||Soil reaction||Hydrologic group|
|Taxonomic Classification||Permeability||Depth to bedrock||Hydric Soil|
|Flooding/Ponding Potential||Potential inclusions|
Map Unit (s): A map unit is a collection of soil areas or miscellaneous areas delineated in a soil map or soil survey. Very simply, the combined individual delineations that are identified by a unique symbol in a survey area are one map unit. Map units identified on the updated soil maps for Plymouth County are identified by numbers and some units have a combination of numbers proceeded by a capitol letter to designate a slope class.
Map Unit Phases: Phases of map units are used to create groupings that are useful in making predictions about soil behavior in soil survey areas. Examples of map unit phases used in Plymouth County are slope phases, stoniness phases and surface layer texture phases.
Taxonomic Classification: Soils are classified according to a national system of classification, referred to as "soil taxonomy". The taxonomic system used to classify soils is a hierarchical system that groups similar chemical and physical properties of soils into common groups. The soil series is the lowest category in Soil Taxonomy and the most common reference term used to name mapping units in soil surveys.
Available water holding capacity (available moisture capacity). The 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 commonly expressed as inches of water per inch of soil. The capacity, in inches, in a 60-inch profile or to a limiting layer is expressed as:
|Very low||0 to 3|
|Low||3 to 6|
|Moderate||6 to 9|
|High||9 to 12|
|Very high||more than 12|
Drainage class (natural). Refers to the frequency and duration of periods of saturation or partial saturation during soil formation, as opposed to altered drainage, which is commonly the result of artificial drainage or irrigation but may be caused by the sudden deepening of channels or the blocking of drainage outlets. Seven classes of natural soil drainage are recognized:
Excessively drained. Water is removed from the soil very rapidly. Excessively drained soils are commonly very coarse textured, rocky, or shallow. Some are steep. All are free of the mottling related to wetness.
SOIL MORPHOLOGY: Typically excessively drained soils have bright matrix colors (high chroma and value) in the upper subsoil which gradually fades with depth to the unweathered color of the underlying geologic material. Some excessively drained soils that have developed within recently deposited sediments (flood plain deposits and coastal dunes) lack color development within the subsoil. Excessively drained soils are not mottled within the upper 5 feet. Soil textures are loamy fine sand or coarser below 10 inches.
Somewhat excessively drained. Water is removed from the soil rapidly. Many somewhat excessively drained soils are sandy and rapidly pervious. Some are shallow. Some are so steep that much of the water they receive is lost as runoff. All are free of the mottling related to wetness.
Well drained. Water is removed from the soil readily, but not rapidly. It is available to plants throughout most of the growing season, and wetness does not inhibit growth of roots for significant periods during most growing seasons. Well drained soils are commonly medium textured. They are mainly free of mottling.
SOIL MORPHOLOGY: Typically well drained soils have bright matrix colors (high chroma and value) in the upper subsoil which gradually fades with depth to the unweathered color of the underlying geologic material. Well drained soils that have developed within recently deposited sediments (floodplain deposits) lack color development. These soils are not mottled within the upper 40 inches. Soil mottling (few, faint and distinct mottles) may be present in some compact glacial till soils above the hardpan layer but are not present in the underlying substratum. Soil textures are typically very fine sand or finer in horizons between 10 to 40 inches.
Moderately well drained. Water is removed from the soil somewhat slowly during some periods. Moderately well drained soils are wet for only a short time during the growing season, but periodically they are wet long enough that most mesophytic crops are affected. They commonly have a slowly pervious layer within or directly below the solum, or periodically receive high rainfall, or both.
SOIL MORPHOLOGY: Typically moderately well drained soils have bright matrix colors (high chroma and value) in the upper subsoil. Moderately well drained soils have distinct or prominent mottles between a depth of 15 and 40 inches below the soil surface.
Somewhat poorly drained. Water is removed slowly enough that the soil is wet for significant periods during the growing season. Wetness markedly restricts the growth of mesophytic crops unless artificial drainage is provided. Somewhat poorly drained soils commonly have a slowly pervious layer, a high water table, additional water from seepage, nearly continuous rainfall, or a combination of these.
Poorly drained. Water is removed so slowly that the soil is saturated 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 mesophytic crops cannot be grown unless the soil is artificially drained. The soil is not continuously saturated in layers directly below plow depth. Poor drainage results from a high water table, a slowly pervious layer within the profile, seepage, ne-arly continuous rainfall, or a combination of these.
SOIL MORPHOLOGY: Typically poorly drained soils are mottled directly below the A horizon. Depending upon soil profile development and soil textures, matrix colors may vary. Soils that exhibit pronounced Spodic development have an albic horizon which has faint to prominent mottles and is underlain by an ortstein or a spodic horizon which is partially cemented or has iron nodules. The Spodic horizon and material directly underlying the spodic have distinct and prominent mottles. Poorly drained soils with very fine sand or finer textures have matrix colors with chroma of 2 or less within 20 inches of the surface. Poorly drained soils with loamy fine sand or coarser textures have matrix colors with chroma of 3 or less within 12 inches of the surface.
Very poorly drained. Water is removed from the soil so slowly that free water remains at or on the surface during most of the growing season. Unless the soil is artificially drained, most mesophytic crops cannot be grown. Very poorly drained soils are commonly level or depressed and are frequently ponded. Yet, where rainfall is high and nearly continuous, they can have moderate or high slope gradients.
SOIL MORPHOLOGY: Typically very poorly drained soils have organic soil materials that extend from the surface to a depth of 16 inches or more, or either have a histic epipedon or an epipedon that has "n" value of greater than 0.7. These soils are generally gleyed directly below the surface layers.
Soil permeability is the quality of the soil that enables water or air to move through it. Accepted, as a measure of this quality is the rate at which a saturated soil transmits water. That rate is the "saturated hydraulic conductivity" of soil physics. In line with conventional usage in the engineering profession and traditional usage in published soil surveys, this rate of flow, principally downward, continues to be expressed as "permeability". It is expressed in inches per hour.
|Slow||0.06 - 0.20|
|moderately slow||0.2 - 0.60|
|moderate||0.6 - 2.0|
|moderately rapid||2.0 - 6.0|
|rapid||6.0 - 20|
Soil reaction: The degree of acidity or alkalinity of a soil, expressed as a pH value. The descriptive terms associated with ranges in pH are:
|Very strongly acid||4.5-5.0|
Depth to bedrock: Bedrock is the solid (fixed) rock underlying soils.
Seasonal high water table:
A seasonal high water table is a zone of saturation at the highest average depth during the wettest season. It is at least 6 inches thick, persists in the soil for more than a few weeks, and is within 6 feet of the soil surface. Soils that have a seasonal high water table are classified according to the depth to water table, kind of water table, and time of year when water table is highest. The normal depth range of a seasonal high water table or zone of saturation of the natural undrained soil is given to the nearest half-foot. Two kinds of seasonal high water tables are recognized within the soil (1) apparent, (2) perched. Another kind is above the soil surface much of the time resulting in ponding.
(1) An apparent water table is the level at which water stands in a freshly dug, unlined borehole after adequate time for adjustments in the surrounding soil.
(2) A perched water table is one that exists in the soil above an unsaturated zone. A water table may be inferred to be perched on the basis of general knowledge of the water levels of an area, the landscape position, the permeability of soil layers, and from other evidence. To prove that a water table is perched, the water levels in boreholes must be observed to fall when the borehole is extended.
Hydrologic group: Link to Hydrologic Soil Groups for Massachusetts soils
A grouping of soils having the same runoff potential under similar storm and cover conditions. Hydrologic groups are used in equations that estimate runoff from rainfall. Soil properties that influence runoff potential are those that influence the minimum rate of infiltration for a bare soil after prolonged wetting and when not frozen. The soils of the U.S. are placed into four groups A, B, C, D. Definitions of the classes are as follows:
Hydric Soil: Hydric soils are soils that are saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions in the upper part. Link to Hydric Soil Website
Flooding is the temporary covering of the soil surface by flowing water from any source, such as streams overflowing their banks, runoff from adjacent or surrounding slopes, inflow from high tide, or any combination of sources.
Ponding is standing water in a closed depression. The water is removed only by deep percolation, transpiration, or evaporation or a combination of these processes. Ponding of soils is classified according to depth, frequency, duration, and beginning and ending months that standing water is observed.
Flooding and Ponding frequency classes are as follows:
|None||No reasonable possibility of flooding|
|Rare||Flooding unlikely but possible under unusual weather conditions|
|Occasional||Flooding is expected infrequently under usual weather conditions.|
|Frequent||Flooding is likely to occur often under unusual weather conditions|
Flooding/ponding duration classes are as follows:
|Extremely brief||0.1 to 4 hours|
|Very brief||4 to 48 hours|
|Brief||2 to 7 days|
|Long||7 days to 1 month|
|Very long||1 month or more|
Potential inclusions: All soil map units contain inclusions of other soil types. The minimum area of delineation for the updated Plymouth County Soil Survey (scale 1:12,000) is approximately 2-3 acres. A map unit has the potential to have inclusions of any soil mapped in southern New England. This list only shows the most common inclusions.
Parent Material: Parent material refers to the geologic sediments the soil formed in. Types of parent material (referred to as the substratum) in Massachusetts soils are broken down into two major categories; glacial deposits and post-glacial deposits. Glacial deposits are mostly of Pleistocene age, and post-glacial deposits are Holocene age. Many soils develop in more than one type of parent material, these soils have a lithologic discontinuity. An example of a soil formed in two parent materials is Broadbrook soils, which formed in silty eolian deposits (Holocene) underlain by dense till (Pleistocene). The following are brief definitions of the dominant soil parent materials for soils in Plymouth County. For a more information about the geology of Plymouth County CLICK HERE.
Glacial Till: Unsorted, non-stratified sediments deposit by glacial ice and typically consisting of a heterogeneous mixture of clay, silt, sand and rock fragments. There are two major types of till; ablation and basal (lodgment) till. Ablation till a very variable but tends to be loose and dominantly sandy but may have lenses of firm loamy material. Canton soils are an example of a soil formed in ablation till. Basal till is usually found on drumlins and till ridges. Basal till tends to have a higher percentage of fines than ablation till and is usually very dense. Paxton soils are an example of a soil formed in basal till.
Glacial Fluvial Deposits (outwash): Fluvial deposits consist of material deposited in meltwater streams flowing from the glacial ice. These deposits consist of stratified sands and gravels on outwash plains, deltas, and eskers. Hinckley soils are an example of a soil formed in fluvial deposits.
Glacial Lacustrine: Sediments deposited in glacial lakes, which have drained or filled with sediments. Lacustrine deposits are typically silty and clayey but can also have strata's of sandy material. A large area of lacustrine soils is located in the Bridgewater /Middleboro area in what geologist refers to as glacial lake Taunton.
POST GLACIAL DEPOSITS
Organic Material: Commonly referred to as Peat or Muck, organic material consisting of dead, decomposing plant material. Thin (less than 8 inches) layers of organic material can be found in the surface layer of upland soils in wooded areas, however, organic soils (soils formed in organic material which is greater than 16 inches) are usually found in bogs or swamps. Freetown, Swansea, and Ipswich soils are organic soils mapped in Plymouth County.
Eolian Deposits: Material transported and deposited by wind, typically consisting of sand and silt. Eolian deposits are found in sand dune areas adjacent to beaches. Most of the surface horizons (A and B horizons) of upland soils have an eolian component associated with them. Hooksan soils are an example of an eolian soil.
Alluvial Sediments: Material deposited by rivers and large streams in present day floodplains.
Human Altered/Transported Material: Commonly referred to as fill, human altered/transported material includes a variety of soil and geologic material deposited by human activity. Areas of human altered material are usually mapped Udorthents or Udipsamments.
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