LOCATION HERMISTON OR+WAEstablished Series
TAXONOMIC CLASS: Coarse-silty, mixed, superactive, mesic Cumulic Haploxerolls
TYPICAL PEDON: Hermiston silt loam, cultivated. (Colors are for moist soil unless otherwise noted.)
Ap--0 to 10 inches; very dark brown (10YR 2/2) silt loam, grayish brown (10YR 5/2) dry; weak medium granular structure; slightly hard, friable, slightly sticky, slightly plastic; many roots; common very fine tubular and many interstitial pores; black plow pan 1/4 inch thick at bottom of horizon; mildly alkaline (pH 7.4); abrupt smooth boundary. (6 to 10 inches thick)
A1--10 to 16 inches; very dark brown (10YR 2/2) silt loam, grayish brown (10YR 5/2) dry; massive; slightly hard, friable, slightly sticky, slightly plastic; many roots; many very fine tubular pores; mildly alkaline (pH 7.8); clear irregular boundary. (2 to 10 inches thick)
A2--16 to 24 inches; dark brown (10YR 3/3) silt loam, grayish brown (10YR 5/2) dry; massive; slightly hard, friable, slightly sticky, slightly plastic; common roots; many very fine and few fine tubular pores; moderately alkaline (pH 8.0); gradual wavy boundary. (0 to 12 inches thick)
Bk1--24 to 42 inches; dark brown (10YR 3/3) silt loam, light brownish gray (10YR 6/2) dry; massive; slightly hard, friable but firmer than horizons above or below, slightly sticky, slightly plastic; common very fine roots; many very fine tubular pores; few firm calcareous nodules 1/8 to 1/2 inches in diameter; strongly effervescent with disseminated and segregated mycelial lime; moderately alkaline (pH 8.1); clear wavy boundary. (12 to 24 inches thick)
Bk2--42 to 60 inches; dark brown (10YR 3/3) silt loam, pale brown (10YR 6/3) dry; massive; slightly hard, friable, slightly sticky, slightly plastic; common very fine roots; many very fine and few fine tubular pores; slightly effervescent with lime mainly disseminated; moderately alkaline (pH 8.0); clear wavy boundary. (12 to 24 inches thick)
C--60 to 70 inches; brown (10YR 4/3) silt loam, light gray (10YR 7/2) dry; few fine brown (7.5YR 4/4) mottles; massive; slightly hard, friable, slightly sticky, slightly plastic; common fine roots; many fine and few medium tubular pores; moderately alkaline (pH 7.9).
TYPE LOCATION: Umatilla County, Oregon; 70 feet west of center of road and 1500 feet north of SE corner sec. 21, T. 2 N., R. 33 E.
RANGE IN CHARACTERISTICS: The soils are moist in some part above 12 inches for at least half the time during the period the soil temperature is above 41 degrees F., in most years but are dry throughout between 4 and 12 inches for 70 to 90 consecutive days during the summer months in most years. The mean annual soil temperature ranges from 49 to 54 degrees F. Thickness of the mollic epipedon ranges from 20 to 30 inches. Depth to secondary lime is 15 to 30 inches. The organic matter decreases irregularly with depth and is greater than 0.5% at depth of 50 inches or more. The 10- to 40- inch control section is commonly silt loam but ranges to very fine sandy loam or silt. Thin lenses, less than 2 inch thick, of fine sandy loam occur below 30 inches. When mixed, it has 10 to 18 percent clay and less than 15 percent coarser than very fine sand.
The A horizon has value of 2 or 3 moist and 4 or 5 dry and chroma of 2 or 3. It has weak or moderate granular or weak very fine to medium subangular blocky structure in the upper part and is massive in the lower part. It is neutral to moderately alkaline.
The Bk horizon has value of 3 or 4 moist, 6 or 7 dry and chroma of 2 or 3. It has firm, calcareous nodules ranging from 0 to 20 percent by volume.
The C horizon has value of 3 through 6 moist and 5 through 8 dry and chroma of 2 or 3. It is mildly to strongly alkaline. Below 30 inches in some pedons, there are very thin, noncalcareous volcanic ash lenses with dry value of 7 or 8.
COMPETING SERIES: These are th Covello, Mondovi, Onyx, Pedigo, Powder and Touchet series. Covello soils have mollic epipedons thicker than 32 inches and are somewhat poorly drained with a permanent water table at about 4 feet. Mondovi soils have moist value of 2 to depths of 40 inches or more and are noncalcareous. Onyx soils are noncalcareous. Pedigo soils are calcareous throughout the mollic epipedon. Powder soils are usually dry. Touchet soils have mottles in the particle-size control section.
GEOGRAPHIC SETTING: Hermiston soils are on stream bottomlands and low terraces at elevations of 200 to 2500 feet. Slopes are 0 to 3 percent. The soil formed in alluvium from silty loess and ash. The climate is semiarid, with moist, cool, winters and dry, warm summers. Mean annual precipitation is 10 to 16 inches. The mean annual temperature is 49 to 54 degrees F. The frost-free period is 130 to 195 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Onyx and Pedigo soils in the bottomlands and the Walla Walla and Nansene soils in the adjacent uplands. Walla Walla soils have mollic epipedons less than 20 inches thick. Nansene soils have a regular decrease in organic carbon and have a mollic epipedon 30 to 50 inches thick.
DRAINAGE AND PERMEABILITY: Well-drained; slow to medium runoff; moderate permeability.
USE AND VEGETATION: Production of dry farmed wheat or irrigated small grains, alfalfa, sugar beets, pasture and hay crops. Native vegetation was mainly giant wildrye and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: Northeastern Oregon and southeastern Washington. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Umatilla County, Oregon 1938.