Prime Farmlands Criteria

1) General.  Prime farmland is land that has the best combination of physical and chemical characteristics for producing food, feed, forage, fiber, and oilseed crops and that is also available for these uses (the land could be cropland , pastureland, rangeland, forest land, or other land but not urban or built-up land or water areas).  It has the soil quality, growing season, and moisture supply needed to produce sustained high yields of crops in an economic manner when treated and managed, including water, according to acceptable farming methods.  In general, prime farmlands have an adequate and dependable water supply from precipitation or irrigation, a favorable temperature and growing season, acceptable levels of acidity or alkalinity, an acceptable content of salt and sodium, and few or no rocks.  They have soils that are permeable to water and air.  Prime farmland is not excessively erodible or saturated with water for a long period of time, and it either does not flood frequently or is protected from flooding.  Examples of soils that qualify as prime farmland are Palouse silt loam, 0 to 7 percent slopes; Brookston silty clay loam, drained; and Tama silty clay loam, 0 to 5 percent slopes.

2) Specific criteria.  Terms used in this section are defined in USDA publications: "Soil Taxonomy, Agriculture Handbook 436;" "Soil Survey Manual, Agriculture Handbook 18;" "Rainfall-Erosion Losses from Cropland, Agriculture Handbook 282;" "Wind Erosion Forces in the United States and Their Use in Predicting Soil Loss, Agriculture Handbook 346;" and "Saline and Alkali Soils, Agriculture Handbook 60."  Prime farmlands meet the following criteria:

(i)  The soils have:

a)  Aquic, udic, ustic, or xeric moisture regimes and a sufficient available water capacity within a depth of 40 inches (1 meter), or in the root zone (the root zone is the part of the soil that is penetrated or can be penetrated by plant roots) if the root zone is less than 40 inches deep, to produce the commonly grown cultivated crops (cultivated crops include, but are not limited to, grain, forage, fiber, oilseed, sugar beet, sugarcane, vegetables, tobacco, orchard, vineyard, and bush fruit crops) adapted to the region in 7 or more years out of 10; or

b)  Xeric or ustic moisture regimes in which the available water capacity is limited, but the area has a developed irrigation water supply that is dependable (a dependable water supply is one in which enough water is available for irrigation in 8 out of 10 years for the crops commonly grown) and of adequate quality; or,

c)  Aridic or torric moisture regimes, and the area has a developed irrigation water supply that is dependable and of adequate quality.

(ii)  The soils have a temperature regime that is frigid, mesic, thermic, or hyperthermic (pergelic and cryic regimes are excluded).  These soils have, at a depth of 20 inches (50 cm), a mean annual temperature higher than 32 degrees Fahrenheit (0 degrees C).  In addition, the mean summer temperature at this depth in soils with an 0 horizon is higher than 47 degrees Fahrenheit (8 degrees C); it is higher than 59 degrees Fahrenheit (15 degrees C) in soils that have no 0 horizon.

(iii)  The soils have a pH between 4.5 and 8.4 in all horizons within a depth of 40 inches (1 meter) or in the root zone if the root zone is less than 40 inches deep.

(iv)  The soils either have no water table or have a water table that is maintained at a sufficient depth during the cropping season to allow cultivated crops common to the area to be grown.

(v)  The soils can be managed so that, in all horizons within a depth of 40 inches (1 meter) or in the root zone if the root zone is less than 40 inches deep, during part of each year the conductivity of the saturation extract is less than 4 mmhos/cm and the exchangeable sodium percentage (ESP) is less than 15.

(vi)  The soils are not flooded frequently during the growing season (less than once in 2 years).

(vii) The product of K (erodibility factor) x percent slope is less than 2.0, and the product of l (soils erodibility) x C (climatic factor) does not exceed 60.

(viii)  The soils have a permeability rate of at least 0.06 inch (0.15 cm) per hour in the upper 20 inches (50 cm), and the mean annual soil temperature at a depth of 20 inches (50 cm) is less than 59 degrees Farenheit (15 degrees C).  The permeability rate is not a limiting factor if the mean annual soil temperature is 59 degrees Farenheit (15 degrees C) or higher.

(ix)  Less than 10 percent of the surface layer (upper 6 inches) in these soils consists of rock fragments coarser than 3 inches (7.6 cm) in diameter.

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