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dependable (a dependable water supply is one in which enough water is <br />available for irrigation in 8 out of 10 years for the crops commonly grown) and <br />of adequate quality; or, <br />(c) Aridic or torric moisture regimes, and the area has a developed irrigation <br />water 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 excluded). These soils have, at a depth of 20 inches <br />(50 cm), a mean annual temperature higher than 32o F (Oo C). In addition, the mean <br />summer temperature at this depth in soils with an 0 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 6.4 in all horizons within a depth of 40 <br />inches (1 meter) or in the root zone if the root zone is less than 40 inches deep. <br />(iv) The soils either have no water table or have a water table that is maintained at a <br />sufficient depth during the cropping season to allow cultivated crops common to the <br />area to be grown. <br />(v) The soils can be managed so that, in all horizons within a depth of 40 inches (1 <br />i meter) or in the root zone if the root zone is less than 40 inches deep, during part of <br />each year the conductivity of the saturation extract is less than 4 mmhos/cm and the <br />exchangeable sodium percentage (ESP) is less than 15. <br />(vi) The soils are not flooded frequently during the growing season (less than once in <br />2 years). <br />(vii) The product of K (erodibility factor) x percent slope is less than 2.0, and the <br />product of I (soils erodibility) x C (climatic factor) does not exceed 60. <br />(viii) The soils have a permeability rate of at least 0.06 inch (0.15 cm) per hour in the <br />upper 20 inches (50 cm), and the mean annual soil temperature at a depth of 20 <br />inches (50 cm) is less than 59o F (1 So C). The permeability rate is not a limiting factor <br />if the mean annual soil temperature is 59o F (15o C) or higher. <br />(ix) Less than 10 percent of the surface layer (upper 6 inches) in these soils consists <br />of rock fragments coarser than 3 inches (7.6 cm) in diameter. <br />(430-VI-NSSH, 1996) <br />(Revised 2/00) 2.04.9-63 <br />