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

174 Soil Survey of
water infiltration. Applying conservation tillage and
conservation cropping systems, farming on the
contour, stripcropping, establishing field windbreaks,
and leaving crop residue on the surface conserve
moisture.
Some of the limitations and hazards shown in the
table cannot be easily overcome. These are flooding,
depth to bedrock, and subsidence.
Additional limitations and hazards are as follows:
Excessive lime.—This limitation can be overcome
by incorporating green manure crops, manure, or crop
residue into the soil; applying a system of
conservation tillage; and using conservation cropping
systems. Also, crops may respond well to additions of
phosphate fertilizer on soils that have a high content of
lime.
Depth to bedrock.—Rooting depth and available
moisture may be limited by bedrock within a depth of
30 inches.
Flooding.—Winter small grain crops can be
damaged. Tilling and planting should be delayed in the
spring until flooding is no longer a hazard.
Gravelly surface layer.—This limitation causes
rapid wear of tillage equipment. It cannot be easily
overcome.
Subsidence.—Subsidence occurs as a result of
shrinkage from drying, consolidation because of the
loss of ground water, compaction from tillage, wind
erosion, burning, and biochemical oxidation. Limiting
the amount of drainage, avoiding excessive tillage,
deferring tillage when the soil is wet, and using a
system of conservation tillage that leaves crop residue
on the surface after planting help to control
subsidence.
Wind erosion.—Using a system of conservation
tillage that leaves crop residue on the surface after
planting and keeping the surface rough help to control
wind erosion.
Explanation of Criteria
Crusting.—The average content of organic matter
in the surface layer is less than 2.5 percent, and the
clay content is greater than 20 percent.
Depth to bedrock.—Bedrock is within a depth of 30
inches.
Excessive lime.—The calcium carbonate equivalent
is 15 percent or more and meets the calcic horizon
classification criteria.
Excessive permeability.—The upper limit of the
permeability range is 6 inches or more within the soil
profile.
Flooding.—The component of the map unit is
occasionally flooded or frequently flooded.
Gravelly surface layer.—The content of gravel in
the surface layer is greater than 15 percent.
Low available water capacity.—The weighted
average of the available water capacity between the
surface and a depth of 40 inches is 0.1 inch or less.
Ponding.—A water table is above the surface.
Poor tilth.—The component of the map unit has 27
percent or more clay in the surface layer.
Restricted permeability.—Permeability is less than
0.2 inch per hour between the surface and a depth of
40 inches.
Subsidence.—The decrease in surface elevation is
more than 0 inches.
Water erosion.—The surface K factor multiplied by
the slope is greater than 0.8, and the slope is 3
percent or more.
Wetness.—The component of the map unit has a
water table within a depth of 1.5 feet.
Wind erosion.—The wind erodibility group (WEG) is
1 or 2.
Crop Yield Estimates
The average yields per acre that can be expected of
the principal crops under a high level of management
are shown in table 7. In any given year, yields may be
higher or lower than those indicated in the table because
of variations in rainfall and other climatic factors. The
land capability classification of map units in the survey
area also is shown in the table.
The yields are based mainly on the experience and
records of farmers, conservationists, and extension
agents (Fehrenbacher and others, 1978). Available
yield data from nearby counties and results of field
trials and demonstrations also are considered.
The management needed to obtain the indicated
yields of the various crops depends on the kind of soil
and the crop. Management can include drainage;
erosion control; protection from flooding; the proper
planting and seeding rates; suitable high-yielding crop
varieties; appropriate and timely tillage; control of
weeds, plant diseases, and harmful insects; favorable
soil reaction and optimum levels of nitrogen,
phosphorus, potassium, and trace elements for each
crop; effective use of crop residue, barnyard manure,
and green manure crops; and harvesting that ensures
the smallest possible loss.
The estimated yields reflect the productive capacity
of each soil for each of the principal crops. Yields are
likely to increase as new production technology is
developed. The relative productivity of a given soil
compared with that of other soils, however, is not likely
to change.