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657.5 Identification of important farmlands.
<br />• (a) Prime farmlands.
<br />(1) General. Prime farmland is land that has the best combination of physical and
<br />chemical characteristics for producing food, feed, forage, fiber, and oilseed crops
<br />and that is also available for these uses (the land could be cropland, pastureland,
<br />rangeland, forest land, or other land but not urban or built-up land or water areas).
<br />It has the soil quality, growing season, and moisture supply needed to produce
<br />sustained high yields of crops In an economic manner when treated and
<br />managed, including water, according to acceptable farming methods. In general,
<br />prime farmlands have an adequate and dependable water supply from
<br />precipitation or irrigation, a favorable temperature and growing season,
<br />acceptable levels of acidity or alkalinity, an acceptable content of salt and sodium,
<br />and few or no rocks. They have soils that are permeable to water and air. Prime
<br />farmland is not excessively erodible or saturated with water for a long period of
<br />time, and it either does not flood frequently or is protected from flooding.
<br />Examples of soils that qualify as prime farmland are Palouse silt loam, O to 7
<br />percent slopes; Brookston silty clay loam, drained; and Tama silty clay loam, O to
<br />5 percent slopes.
<br />(2) Specific criteria. Terms used in this section are defined in USDA publications:
<br />"Soil Taxonomy, Agriculture Handbook 436;" "Soil Survey Manual, Agriculture
<br />Handbook 18;" "Rainfall-Erosion Losses from Cropland, Agriculture Handbook
<br />282;" "Wind Erosion Forces in the United States and Their Use in Predicting Soil
<br />Loss, Agriculture Handbook 346;" and "Saline and Alkali Soils, Agriculture
<br />Handbook 60." Prime farmlands meet all the following criteria:
<br />• (i) The soils have:
<br />(a) Aquic, udic, ustic, or xeric moisture regimes and a sufficient
<br />available water capacity within a depth of 40 inches (1 meter), or in
<br />the root zone (the root zone is the part of the soil that is penetrated
<br />or can be penetrated by plant roots) if the root zone is less than 40
<br />inches deep, to produce the commonly grown cultivated crops
<br />(cultivated crops include, but are not limited to, grain, forage, fiber,
<br />oilseed, sugar beet, sugarcane, vegetable, tobacco, orchard,
<br />vineyard, and bush fruit crops) adapted to the region in 7 or more
<br />years out of 10; or
<br />(b) Xeric or ustic moisture regimes in which the available water
<br />capacity is limited, but the area has a developed irrigation water
<br />supply that is dependable (a dependable water supply is one in
<br />which enough water is available for irrigation in 8 out of 10 years for
<br />the crops commonly grown) and of adequate quality; or,
<br />(c) Aridic or tonic moisture regimes, and the area has a developed
<br />irrigation water supply that is dependable and of adequate quality.
<br />(ii) The soils have a temperature regime that is frigid, mesic, thermic, or
<br />hyperthermic (pergelic and cryic regimes are excluded). These soils have,
<br />at a depth of 20 inches (50 cm), a mean annual temperature higher than
<br />32o F (Oo C). In addition, the mean summer temperature at this depth in
<br />• (REVISED 9/99) 2.04.9-59
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