|
• 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 chemical characteristics for
<br />producing food, feed, forage, fiber, and oilseed crops and that is also available for these uses (the land could be
<br />cropland, pastureland, rangeland, forest land, or other land but not urban or built-up land or water areas). It has the
<br />soil quality, growing season, and moisture supply needed to produce sustained high yields of crops in an economic
<br />manner when treated and managed, induding water, according to acceptable farming methods. In general, prime
<br />farmlands have an adequate and dependable water supply from precipitation or irrigation, a favorable temperature
<br />and growing season, acceptable levels of acidity or alkalinity, an acceptable content of salt and sodium, and few
<br />or no rocks. They have soils that are permeable to water and air. Prime farmland is not excessivety erodible or
<br />saturated with water for a long period of 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 percent slopes; Brookston silty day
<br />loam, drained; and Tama silty clay loam, O to 5 percent slopes.
<br />(2) Speck criteria. Terms used in this section are defined in USDA publications: "Soil Taxonomy, Agriculture
<br />Handbook 436;" "Soil Survey Manual, Agriculture Handbook 18;" "Rainfall-Erosion Losses from Cropland,
<br />Agriculture Handbook 282;" "Wind Erosion Forces in the United States and Their Use in Predicting Soil Loss,
<br />Agriculture Handbook 346;" and "Saline and Alkali Soils, Agriculture Handbook 60 "Prime farmlands meet all the
<br />• following criteria:
<br />(i) The soils have:
<br />(a) Aquic, udic, ustic, or xeric moisture regimes and a sufficient available water capadtywithin a depth of 40 inches
<br />(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
<br />roots)'if the root zone is less than 40 inches deep, to produce the commony grown cultivated crops (cultivated crops
<br />include, but are not limited to, grain, forage, fiber, oilseed, sugar beet, sugarcane, vegetable, tobacco, orchard,
<br />vineyard, and bush fruit 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 capaciiy is limited, but the area has a developed
<br />irrigation water supply that is dependable (a dependable water supply is one in which enough water is available for
<br />irrigation 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 supply that is dependable and
<br />of adequate quality.
<br />(ii) The soils have a temperature regime that is frigid, mesic, thermic, or hyperthermic (pergelic and cryic regimes
<br />are exduded). These soils have, at a depth of 20 inches (50 cm), a mean annual temperature higher than 32o F
<br />(Oo C). In addition, the mean summer temperature at this depth in soils with an O horizon is higher than 47o F (80
<br />C); it is higher than 59o F (15o C) in soils that have no O horizon.
<br />(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
<br />if the root zone is less than 40 inches deep.
<br />
<br />(Revised March 2006) Attachment 2.04.9-3-39
<br />
|