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• 657.5 Ident~cation of important farmlands.
<br />(a) Prime farmlands.
<br />(1) General. Prime farmland is land that has the best combination of physical and chemical characteristics
<br />for producing food, feed, forage, fiber, and oilseed crops and that is also available for these uses (the land
<br />could be cropland, pastureland, rangeland, forest land, or other land but not urban or built-upland orwater
<br />areas). It has the soil quality, growing season, and moisture supply needed to produce sustained high
<br />yields of crops in an economic manner when treated and managed, including water, according to
<br />acceptable farming methods. In general, prime farmlands have an adequate and dependable water supply
<br />from precipitation or irrigation, a favorable temperature and growing season, acceptable levels of acidity
<br />or alkalinity, an acceptable content of salt and sodium, and few or no rocks. They have soils that are
<br />permeable to water and air. Prime farmland is not excessively erodible or saturated with water for a long
<br />period of time, and it either does not flood frequently or is protected from flooding. Examples of soils that
<br />qualify as prime farmland are Palouse silt loam, O to 7 percent slopes; Brookston silty Gay loam, drained;
<br />and Tama silty day loam, O to 5 percent slopes.
<br />(2) Specific criteria. Terms used in this section are defined in USDA publications: "Soil Taxonomy,
<br />Agriculture Handbook 436;" "Soil Survey Manual, Agriculture Handbook 18 ""Rainfall-Erosion Losses from
<br />Cropland, Agriculture Handbook 282;" "Wind Erosion Forces in the United States and Their Use in
<br />Predicting Soil Loss, Agriculture Handbook 346;" and "Saline and Alkali Soils, Agriculture Handbook 60."
<br />• Prime farmlands meet all the following criteria:
<br />(i) The soils have:
<br />(a) Aquic, udic, usfic, or xeric moisture regimes and a sufficient available water capacity
<br />within a depth of 40 inches (1 meter), or in the root zone (the root zone is the
<br />part of the soil that is penetrated or can be penetrated by plant roots) 'if the root
<br />zone is less than 40 inches deep, to produce the commonly grown cultivated
<br />crops (cultivated crops indude, but are not limited to, grain, forage, fiber, oilseed,
<br />sugar beet, sugarcane, vegetable, tobacco, orchard, vineyard, and bush fruit
<br />crops) adapted to the region in 7 or more years out of 10; or
<br />(b) Xeric or ustic moisture regimes in which the available water capacity is limited, but
<br />the area has a developed irrigation water supply that is dependable (a
<br />dependable water supply is one in which enough water is available for irrigation
<br />in 8 out of 10 years for the crops commonly grown) and of adequate quality, or,
<br />(c) Aridic or tonic moisture regimes, and the area has a developed irrigation water
<br />supply that is dependable and of adequate quality.
<br />(ii) The soils have a temperature regime that is frigid, mesic, thermic, or hyperthermic
<br />(pergelic and cryic regimes are exduded). These soils have, at a depth of 20
<br />inches (50 cm), a mean annual temperature higher than 32o F (Oo C). In
<br />• addition, the mean summer temperature at this depth in soils with an O horizon
<br />(Revised March 2006) Attachment 2.04.9-4-2
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