Soil Survey of McHenry County, Illinois Part I - Soil Data Mart

18 Soil Survey of
sand than loess typically does. Thickness of the silty
material generally ranges from 2.0 to 3.5 feet west of
the Marengo Ridge. The ridge itself and areas to the
east generally have a loess cover less than 2 feet
thick. Proctor soils formed in silty material and in the
underlying outwash.
Organic material consists of plant remains. After the
glaciers receded, water was left standing in various
landform depressions. These areas were very wet
during the time of soil formation. As a result, the
decaying grasses and sedges accumulated more
rapidly than the rate of decomposition. Most of the
plant material has decomposed to a point where it is
not recognizable. These organic deposits are called
muck. Houghton soils formed in this organic material.
Alluvium is material recently deposited by streams.
It varies in texture, depending on the speed of the
water from which it was deposited. Millington soils
formed in loamy alluvium.
Lacustrine material was deposited from still or
ponded glacial meltwater. After the coarser fragments
were deposited as outwash by moving water, the finer
particles, such as very fine sand, silt, and clay, settled
in still water. Martinton soils formed in lacustrine
deposits.
A very small area on the western edge of the
county formed in glacial drift that is moderately deep
over limestone bedrock. Rockton soils formed in this
material.
Climate
McHenry County has a temperate, humid
continental climate. The general climate has had an
important overall influence on the characteristics of the
soils. Climate is essentially uniform throughout the
county, however, and has not caused any major
differences among the soils.
Climate has very important effects on weathering,
vegetation, and erosion. The weathering of minerals in
the soil increases as temperature and rainfall
increase. As water moves downward, clay is moved
from the surface soil to the subsoil, where it
accumulates. The water also dissolves soluble salts
and leaches them downward. Climate also influences
the kind and extent of plant and animal life. The
climate in McHenry County has favored prairie grass
and hardwood forests. Heavy rains can harm exposed
areas of soils that have been farmed. Spring rains and
wind can cause extensive erosion when crop residue
and trees are removed from the surface. More soil will
be lost through erosion each year than is formed by
natural processes.
Living Organisms
Soils are affected by the vegetation under which
they formed. The main contribution of the vegetation
and biological processes is the addition of organic
matter and nitrogen to the soil. The amount of organic
material in the soil depends on the kind of native
plants that grew on the soil. Grasses have many fine
fibrous roots that add large amounts of organic matter
to the soil when they die and decay. Soils that formed
under prairie vegetation, therefore, have a thick, black
or dark brown surface layer. Parr, Ringwood, Warsaw,
and Waupecan soils formed under prairie vegetation.
In contrast, the soils whose native vegetation was
deciduous trees have a thin, light-colored surface
layer because less organic matter is added to the soil
by tree roots than by the prairie vegetation. Casco,
Kidami, and Kidder soils formed under forest
vegetation.
Bacteria, fungi, and other micro-organisms help to
break down the organic matter and thus provide
nutrients for plants and other soil organisms. The
stability of soil aggregates, which are structural units
made up of sand, silt, and clay, is affected by microbial
activity because cellular excretions from these
organisms help to bind soil particles together. Stable
aggregates help to maintain soil porosity and promote
favorable relationships among soil, water, and air.
Moreover, earthworms, crayfish, insects, and
burrowing animals tend to incorporate organic matter
into the soil and help to keep soils open and porous.
Relief
Relief, which includes elevation, topography, and
water table levels, largely determines the natural
drainage of soils. In McHenry County, the slopes
range from 0 to 30 percent. Natural soil drainage
classes range from well drained on the side slopes
and ridges to very poorly drained in depressions.
Relief affects the depth to the seasonal high water
table or natural drainage of the soil by influencing
infiltration and runoff rates. The poorly drained
Dunham and Selmass soils are in low-lying, nearly
level areas and have a water table close to the surface
for most of the year. The soil pores contain water,
which restricts the circulation of air in the soil. Under
these conditions, iron and manganese compounds are
chemically reduced. As a result, the subsoil is dull
gray and mottled. In the more sloping, well drained
Griswold soils, the water table is lower and some of
the rainfall runs off the surface. The soil pores contain
less water and more air. The iron and manganese