LOCATION PORONTO MT
Established Series
Rev. HAL-EMM-KLS
01/2023
PORONTO SERIES
The Poronto series consists of very deep, poorly drained soils that formed in alluvium. These soils are on stream terraces, floodplains and depressions. Slopes are 0 to 4 percent. Mean annual precipitation is about 380 mm, and mean annual air temperature is about 5 degrees C.
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Typic Endoaquolls
TYPICAL PEDON: Poronto loam, in pasture (colors are for moist soil unless otherwise noted).
Oi--0 to 8 cm; slightly decomposed organic matter. (5 to 10 cm thick)
A--8 to 33 cm; very dark gray (10YR 3/1) loam, grayish brown (10YR 5/2) dry; common fine distinct strong brown (7.5YR 5/8) redox concentrations; moderate medium granular structure; very hard, firm, moderately sticky and slightly plastic; many fine and very fine roots; many fine and very fine interstitial pores; slightly effervescent; slightly alkaline (pH 7.8); clear smooth boundary. (18 to 40 cm thick)
Bg1--33 to 48 cm; dark gray (5YR 4/1) very gravelly silty clay loam, light gray (5YR 7/1) dry; many medium distinct strong brown (7.5YR 5/8) redox concentrations; weak medium subangular blocky structure; very hard, friable, slightly sticky and slightly plastic; many fine and very fine roots; many fine and very fine interstitial pores; 40 percent gravel; slightly alkaline (pH 7.4); gradual wavy boundary.
Bg2--48 to 78 cm; dark gray (5YR 4/1) very gravelly clay loam, light gray (5YR 7/1) dry; many fine distinct yellowish red (5YR 4/6) redox concentrations; weak medium subangular blocky structure; hard, friable, slightly sticky and moderately plastic; common fine and very fine roots; many fine and very fine interstitial pores; 40 percent gravel; neutral; (pH 7.2); gradual wavy boundary. (Combined thickness of Bg1 and Bg2 horizons - 30 to 60 cm)
Bg3--78 to 159 cm; dark gray (5YR 4/1) very gravelly sandy loam, gray (5YR 6/1) dry; few fine distinct strong brown (7.5YR 5/8) redox concentrations; weak medium subangular blocky structure; soft, very friable, nonsticky and nonplastic; few fine and very fine roots; many fine and very fine irregular pores; 45 percent gravel; neutral (pH 7.2).
TYPE LOCATION: Powell County, Montana; about 580 meters south and 105 meters east of the NW corner of sec. 11, T. 6 N., R. 10 W.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature--5 to 8 degrees C
Moisture control section--10 to 30 cm
Mollic epipedon thickness--25 to 40 cm
Depth to seasonal high water table--30 to 60 cm
A horizon
Hue--10YR or 2.5Y
Value--2 or 3 moist; 2 through 5 dry
Chroma--1 or 2; dry or moist
Clay content--18 to 35 percent
Rock fragment content--0 to 15 percent total; 0 to 10 percent gravel, 0 to 5 percent cobbles
Reaction--pH 6.6 to 7.8
Bg1 horizon
Hue--10YR, 7.5YR, 5YR, 5Y, or 2.5Y
Value--3 or 4 moist; 4 through 7 dry
Chroma--1 through 3; dry or moist
Texture--loam, clay loam, sandy clay loam, or silty clay loam
Clay content--18 to 35 percent
Rock fragment content--35 to 60 percent total; 25 to 40 percent gravel, 0 to 20 percent cobbles
Reaction--pH 6.6 to 7.8
Bg2 horizon
Hue--10YR, 7.5YR, 5YR, 5Y, or 2.5Y
Value--3, 4, or 5 moist; 5, 6, or 7 dry
Chroma--1, 2, or 3; dry or moist
Texture--clay loam, sandy clay loam, or loam
Clay content--18 to 35 percent
Rock fragment content--35 to 60 percent total; 35 to 40 percent gravel, 0 to 20 percent cobbles
Reaction--pH 6.6 to 7.8
Bg3 horizon
Hue--10YR, 7.5YR, 5YR, 2.5Y, or 5Y
Value--3, 4, or 5 moist; 4, 5, 6, or 7 dry
Chroma--1 or 2; dry or moist
Texture--sandy loam or sandy clay loam
Clay content--15 to 30 percent
Rock fragment content--35 to 60 percent total; 35 to 45 percent gravel, 0 to 15 percent cobbles
Reaction--pH 6.6 to 7.3
COMPETING SERIES:
Allwit (ID) - texture average is sandy loam and does not have Bg horizons
Irim (CO) - have an Ag horizon
Lehmandow (NV) - have a seasonal high water table between 15 and 30 cm between March and May
Mcalla (MT) - have a C horizon with loamy sand, loamy coarse sand or sand textures
Swampcreek (MT) - have horizons of secondary carbonate accumulation; have a lithologic discontinuity
GEOGRAPHIC SETTING:
Landform--stream terraces, flood plains and depressions
Elevation--1100 to 1890 meters
Slope--0 to 4 percent
Parent material--alluvium
Climate--long, cold winters; moist springs; warm summers
Mean annual precipitation--250 to 480 mm, much of which falls as snow or rain in the spring
Mean annual air temperature--4 to 7 degrees C
Frost-free period--70 to 105 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed
DRAINAGE AND PERMEABILITY: Poorly drained, moderate permeability
USE AND VEGETATION: Poronto soils are used for hayland and pasture. The native vegetation is tall reedgrass, mannagrass, tufted hairgrass, blue-eyed grass and willow.
DISTRIBUTION AND EXTENT: Poronto soils are of small extent in southwestern Montana; MLRAs 43B and 44B.
SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Powell County, Montana, 1995
REMARKS: Soil interpretation record: MT1393
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon--8 to 33 cm (A horizon)
Cambic horizons--33 to 159 cm (Bg1, Bg2, Bg3 horizons)
Particle-size control section--25 to 100 cm (part of the A horizon, all of the Bg1 and Bg2 horizons, and part of the Bg3 horizon)
Poronto soils have a frigid temperature regime and an aquic soil moisture regime.
Converted to metric and O horizons were updated to start at zero. Competing series section was not updated. 01/2023
National Cooperative Soil Survey
U.S.A.