LOCATION KNULL IDEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Xeric Natrargids
TYPIFYING PEDON: Knull silt loam, big sagebrush and grass. (Colors for dry soil unless otherwise noted.)
A11--0 to 2 inches; grayish brown (10YR 5/2) silt loam, very dark grayish brown (10YR 3/2) moist; weak very fine granular structure; soft, very friable, nonsticky, slightly plastic; many very fine and fine roots; many very fine interstitial pores; noncalcareous; mildly alkaline (pH 7.8); clear smooth boundary. (0 to 2 inches thick)
A12--2 to 7 inches; grayish brown (10YR 5/2) (light brownish gray 10YR 6/2 crushed) heavy silt loam, dark brown (10YR 3/2) moist; slightly darker coating on peds; moderate fine and very fine subangular and angular blocky structure; hard, firm, slightly sticky, slightly plastic; common very fine and fine roots; common very fine tubular pores; very few krotovinas; thin patchy clay films on surfaces of peds and medium patchy ones in pores; slightly calcareous; mildly alkaline (pH 7.8); gradual wavy boundary. (2 to 8 inches thick)
B2t--7 to 11 inches; brown (10YR 5/3) (pale brown 10YR 6/3 crushed) heavy silt loam, dark brown (10YR 3/3) moist; slightly darker coating on peds; moderate fine and very fine subangular and angular blocky structure; hard, firm, slightly sticky, slightly plastic; common very fine and fine roots; common very fine tubular pores; very few krotovinas; thin patchy clay films on surfaces of peds and medium patchy ones in pores; slightly calcareous; mildly alkaline (pH 7.8); gradual wavy boundary. (3 to 7 inches thick)
B3tsa--11 to 16 inches; very pale brown (10YR 7/3) heavy silt loam, brown (10YR 4/3) moist; moderate very fine and fine subangular blocky structure; hard, firm, slightly sticky, slightly plastic; few very fine and fine subangular blocky structure; hard, firm, slightly sticky, slightly plastic; few very fine and fine roots; common very fine tubular pores; few 4 or 5 mm worm krotovinas; many firm nodules (cicada krotovinas); few thin clay films on surfaces of peds and thin patchy ones in some pores; few fine white salt veins and spots; strongly calcareous; moderately alkaline (pH 8.3); gradual wavy boundary. (2 to 7 inches thick)
C1casa--16 to 23 inches; light gray (10YR 7/2) silt loam, brown (10YR 5/3) moist; weak medium and thick platy structure that parts to weak fine angular blocky structure; hard, friable, slightly sticky, slightly plastic; few very fine and fine roots; few very fine tubular pores; many hard, firm or very firm nodules (cicada krotovinas) which slake in HC1; strongly calcareous, few fine veins and spots of lime; moderately alkaline (pH 8.4); gradual wavy boundary. (6 to 15 inches thick)
C2casa--23 to 40 inches; light gray (10YR 7/2) silt loam, grayish brown (10YR 5/2) moist; massive; slightly hard, friable, nonsticky, slightly plastic; few very fine and fine roots; few very fine tubular pores; common hard or very hard 0.8 inch nodules (cicada krotovinas); strongly calcareous; few lime veins; moderately alkaline (pH 8.4); gradual wavy boundary. (5 to 20 inches thick)
C3--40 to 57 inches; light gray (10YR 7/2) silt loam, dark grayish brown (10YR 5/2) moist; massive; slightly hard, very friable, nonsticky, nonplastic; few fine roots; few very fine tubular pores; strongly calcareous, few lime veins; moderately alkaline (pH 8.4); gradual wavy boundary. (0 to 20 inches thick)
C4--57 to 70 inches; light gray (10YR 7/2) silt loam, dark grayish brown (10YR 4/2) moist; massive; slightly hard, very friable, nonsticky, nonplastic; few fine roots; few very fine tubular pores; moderately calcareous, few fine lime veins; strongly alkaline (pH 9.0). (0 to 30 inches thick)
TYPE LOCATION: Bannock County, Idaho; 115 feet east and 120 feet north of the southwest corner of the NW1/4 NW1/4 sec. 5, T.5S., R.36E.
RANGE IN CHARACTERISTICS: The mean annual soil temperature ranges from 47 degrees to 55 degrees F. The soils are usually dry but are moist in some part between depths of 4 and 12 inches for about 60 to 70 days during the spring and early summer. The sola range in thickness from 6 to 18 inches. Depth to the calcic horizon is 8 to 20 inches. The natric horizon is predominantly silt loam and averages 18 and 27 percent clay and less than 15 percent particles coarser than very fine sand. The A horizon has value of 5 or 6.5 dry or 3 to 4.5 moist, and chroma of 2 or 3. However, it is not both darker than value of 5.5 dry and 3.5 moist, both broken and crushed, when mixed to a depth of 7 inches. This horizon is neutral to moderately alkaline (pH 6.7 to 8.0). Tillage often mixes the A horizon and part of the Bt horizon. Where cultivate, a thin Bt horizon is in most pedons. The Bt horizon has value of 5 through 7 dry and 3 to 4.5 moist. It has moderate or weak prismatic or columnar structure that parts to moderate or strong subangular or angular blocky structure. This horizon is neutral to strongly alkaline (pH 6.8 to 8.6). All or part of the Bt horizon is slightly or moderately saline and contains 15 to 40 percent exchangeable sodium. Where undisturbed, the A and the upper part or al of the Bt horizons are noncalcareous. The organic matter content of the upper 15 inches averages more than 1 percent if the weighted average sand/clay ration for this depth is 1.0 or less. The Cca horizon has value of 6 through 8 dry and 4 through 6 moist, and chroma of 2 or 3. It contains about 15 to 28 percent calcium carbonate equivalent. This horizon is mildly to strongly alkaline (pH 7.7 to 8.8), slightly to strongly saline, and contains 20 to 60 percent exchangeable sodium.
COMPETING SERIES AND ThEIR DIFFERENTIAE: These are the Brunt, Calabar, Mellor, and Sebree series. Brunt and Calabar soils have a mean annual soil temperature colder than 47 degrees F. Mellor soils are moderately or strongly calcareous in the A and B2t horizon. Sebree soils have a duripan.
SETTING: The soils are in level to rolling loess-covered basalt and other plains and terraces at elevations of 3,000 to 4,800 feet. Slopes are 0 to 4 percent. The soils formed in deep loess or silty alluvium. The climate is semiarid and has dry summers. Mean annual precipitation is 8 to 12 inches, including 1.5 to 4 feet of snowfall. Average freeze-free period is 100 to 155 days.
PRINCIPAL ASSOCIATED SOILS: These are the Portino, Portneuf, and Trevino soils which lack natric horizons.
DRAINAGE AND PERMEABILITY: Well-drained; medium runoff; slow permeability in the B2t horizon and moderately slow permeability in the C horizons.
USE AND VEGETATION: Much is cultivated and irrigated to produce pasture, hay, small grains, sugar beets, and potatoes. Some is nonirrigated and used for range. The principal native plants are stunted big sagebrush, bluebunch wheatgrass, hawksbeard, cheatgrass, squirreltail, Sandberg bluegrass, aster, phlox, and in places greasewood, halogeton, peppergrass, and Russian thistle.
DISTRIBUTION AND EXTENT: The series is inextensive in southern Idaho. Most areas are very small and are mapped as complexes with Portneuf or Portino soils.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Bannock County, Idaho, 1972.
REMARKS: These soils were classified formerly as Solodized Solonetz soils.