Soil Survey of McHenry County, Illinois Part I - Soil Data Mart

McHenry County, Illinois—Part II 177
for these uses. Urban or built-up land, public land, and
water areas cannot be considered prime farmland.
Urban or built-up land is any contiguous unit of land 10
acres or more in size that is used for such purposes
as housing, industrial, and commercial sites, sites for
institutions or public buildings, small parks, golf
courses, cemeteries, railroad yards, airports, sanitary
landfills, sewage treatment plants, and water-control
structures. Public land is land not available for farming
in National forests, National parks, military
reservations, and state parks.
Prime farmland soils commonly receive an
adequate and dependable supply of moisture from
precipitation or irrigation. The temperature and
growing season are favorable, and the level of acidity
or alkalinity and the content of salts and sodium are
acceptable. The soils have few, if any, rocks and are
permeable to water and air. They are not excessively
erodible or saturated with water for long periods, and
they are not frequently flooded during the growing
season or are protected from flooding. Slopes range
mainly from 0 to 6 percent.
Soils that have a high water table, are subject to
flooding, or are droughty may qualify as prime
farmland where these limitations are overcome by
drainage measures, flood control, or irrigation. Onsite
evaluation is necessary to determine the effectiveness
of corrective measures. More information about the
criteria for prime farmland can be obtained at the local
office of the Natural Resources Conservation Service.
A recent trend in land use has been the conversion
of prime farmland to urban and industrial uses. The
loss of prime farmland to other uses puts pressure on
lands that are less productive than prime farmland.
About 264,000 acres, or nearly 66 percent of the
survey area, meets the criteria for prime farmland.
Areas of this land are throughout the county.
The map units in the survey area that meet the
criteria for prime farmland are listed in table 9. This list
does not constitute a recommendation for a particular
land use. On some soils included in the table,
measures that overcome limitations are needed. The
need for these measures is indicated in parentheses
after the map unit name. The location of each map unit
is shown on the detailed soil maps. The soil qualities
that affect use and management are described in the
section “Soil Series and Detailed Soil Map Units” in
Part I of this survey.
Unique farmland is land other than prime farmland
that is used for the production of specific high-value
food and fiber crops. It has the special combination of
soil qualities, location, growing season, and moisture
supply needed for the economic production of
sustained high yields of a specific high-quality crop
when treated and managed by acceptable farming
methods. Examples of such crops are citrus, tree nuts,
olives, cranberries, and vegetables.
Unique farmland is used for a specific high-value
food or fiber crop; has an adequate supply of available
moisture for the specific crop because of stored
moisture, precipitation, or irrigation; and has a
combination of soil qualities, growing season,
temperature, humidity, air drainage, elevation, aspect,
and other factors, such as nearness to markets, that
favors the production of a specific food or fiber crop.
Lists of unique farmland are developed as needed
in cooperation with conservation districts and others.
Additional farmland of statewide importance is land
other than prime farmland and unique farmland that is
of statewide importance in the production of food,
feed, fiber, forage, and oilseed crops. The criteria used
in defining and delineating areas of farmland of
statewide importance are determined by the
appropriate state agency or agencies. Generally,
additional farmland of statewide importance includes
areas that nearly meet the criteria for prime farmland
and that economically produce high yields of crops
when treated and managed by acceptable farming
methods. Some areas can produce as high a yield as
areas of prime farmland if conditions are favorable. In
some states, additional farmland of statewide
importance may include tracts of land that have been
designated for agriculture by state law.
Additional farmland of local importance consists of
areas that are of local importance in the production of
food, feed, fiber, forage, and oilseed crops and are not
identified as having national or statewide importance.
Where appropriate, this land is identified by local
agencies. It may include tracts of land that have been
designated for agriculture by local ordinance.
Lists of this land are developed as needed in
cooperation with conservation districts and others.
Erosion Factors
Soil erodibility (K) and soil-loss tolerance (T) factors
are used in an equation that predicts the amount of
soil lost through water erosion in areas of cropland.
The procedure for predicting soil loss is useful in
guiding the selection of soil and water conservation
practices. The erosion factors for the soils in the
survey area are listed in table 19.
Soil Erodibility (K) Factor
The soil erodibility (K) factor indicates the
susceptibility of a soil to sheet and rill erosion by
water. The soil properties that influence erodibility are