Iowa and Missouri
37,110 km2 (14,330 mi2)
Land use: Nearly all this area is in farms, and about 55
percent is cropland. Corn, soybeans, other feed grains,
and hay are the principal crops. About 25 percent of
the area is in introduced and native grasses, and
about 10 percent is woodland. Beef cattle and swine
are important sources of income on many farms.
Conservation practices are used to reduce erosion,
flooding, and sedimentation.
Elevation and topography: Elevation ranges from
200m in the lowest valleys to 300m on the highest
ridges. This dissected till plain has a thin mantle of
loess. Slopes are mostly rolling to hilly but some
broad ridgetops are nearly level to undulating. The
slopes bordering major stream valleys are steep. A
few large rivers have nearly level broad valley floors.
Local relief is mainly several meters to 25 or 50m,
but the upland flats and valley floors have local relief
of only 1 or 2m.
Climate: Average annual precipitation-825 to 1,025
mm. About two-thirds of the precipitation falls during the freeze-free period. The low precipitation in
winter is snow. Average annual temperature-10 to
13°C. Average freeze-free period-160 to 180 days.
Water: In most years the favorably distributed moderate precipitation provides enough water for crops.
The many small perennial streams and a few large
streams are additional sources of water but are little
used for these purposes. Ground-water supplies are
small and undependable. The stream flow fluctuates
severely and frequently.
Soils: Most of the soils are Udolls. They are deep and
have a medium textured surface layer and a fine
textured subsoil. They have a mesic temperature
regime, an udic moisture regime, and montmorillonitic
mineralogy. Somewhat poorly drained, nearly level
to moderately sloping Argiudolls (Haig series) and
Ochraqualfs (Kilwinning, Kniffin, and Pershing series) and nearly level to moderately sloping, poorly
drained, Argialbolls (Edina series), are on upland
divides on loess-covered till plains. Somewhat poorly
drained, gently sloping to strongly sloping Argiudolls
(Adair, Lagonda, and Lamoni series) and poorly
drained, gently sloping to strongly sloping Argiaquolls
(Clarinda series) are on convex side slopes with a thin
mantle of loess or pedisediment over glacial till. Well
drained and moderately well drained, moderately
sloping to steep Argiudolls (Shelby series) and
Hapludalfs (Armster, Armstrong, Gara, Keswick,
and Lindley series) are on side slopes on clay loam
glacial till. Moderately well drained Hapludolls
(Kennebec and Lawson series) and Udifluvents
(Nodaway series) are on silty alluvium flood plains.
Poorly drained and very poorly drained Haplaquolls
(Chequest, Colo, Zook, and Wabash series) and somewhat poorly drained Argialbolls (Vesser series) are
on clayey alluvium flood plains.
Potential natural vegetation: This area supports
grassland vegetation. Big bluestem, indiangrass, little bluestem, and switchgrass are the major species.
The natural drainageways and the lowland soils interspersed throughout the area support forest vegetation. Oak and hickory species are dominant. Most
of the native grasses have disappeared because of
cultivation and overgrazing. Naturalized bluegrass is
prevalent on noncultivated areas.
Data Source:
U. S. Department of Agriculture, Soil Conservation Service. 1981.
Land Resource Regions and Major Land Resource Areas of the United States.
Agriculture Handbook 296.U. S. Government Printing Office, Washington, D. C.
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