Estimating your soil erosion losses with the universal soil loss equation (USLE)

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!■■■■ Cooperative Extension Service ■College of Agriculture ■■ Circular 1220
■■■■■ University of Illinois at Urbana-Champaign IBBIBBII

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TABLE OF CONTENTS

Illinois Erosion Control Program 1

The Universal Soil Loss Equation (USEE) 1

Rainfall (R) Factor 2

Soil Erodibility (K) Factor 2

Slope Length and Steepness (LS) Factor 3

Cropping and Management (C) Factor 3

Conservation Practices (P) Factor 5

Using the USEE 6

Working through Some Examples 6

Solving the USEE for C 7

Getting Help 7

Tables 8-16

Appendix: How to Make and Use a Slope Gauge 17

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

Table 9.

Table 10

Tables

Soil Erodibility (K) and Erosion Tolerance (T) Values

for Specific Illinois Soils 8

Soil Erodibility (K) Values for Certain General Soil Types 11

Slope Length and Steepness (LS) Values for Specific Combinations

of Length and Steepness 11

Cropping and Management (C) Values for Northern Illinois 12

Cropping and Management (C) Values for Central Illinois 13

Cropping and Management (C) Values for Southern Illinois 14

C Values for Permanent Pasture, Range, and Idle Land 15

C Values for Undisturbed Forest Land 15

Conservation Practices (P) Values for Contour Farming

and Contour Strip Cropping 16

Values Used in Determining P Values for Terraces Built on Contour and
Used in Combination with Contour Farming and Contour Strip Cropping ... 16

This circular was prepared by Robert D. Wall<er, Extension natural
resources specialist, and Robert A. Pope, former Extension agron-
omist, University of Illinois at Urbana-Champaign. The authors
would like to thank Steve Probst, Soil Conservation Service, for his
careful review and helpful suggestions.

Information in this circular is based on Agricultural Handbook 537 published by the Science and Education
Administration, U.S. Department of Agriculture, and generally corresponds with information contained in the
Soil Conservation Service's Illinois Technical Guide.

Excessive soil erosion occurs on 40 percent, or
9.6 million acres, of Illinois cropland. Erosion
on this land exceeds the soil loss tolerances of
one to five tons per acre annually, with a high of
over 50 tons per acre and an average of 1 1. 7 tons.
In addition, 23 percent, or 700,000 acres, of
pastureland and 16 percent, or 600,000 acres, of
woodland have excessive soil erosion.

The loss of valuable topsoil to erosion is
compounded by the loss of plant nutrients and
organic matter and by more difficulty in tilling
since the soil becomes increasingly clayey as
more subsoil is brought to the surface. But the
problems of erosion are not confined to farm-
land. The sediment that leaves fields often has
an adverse effect on the water quality and
condition of drainage ditches, lakes, reservoirs,
and streams. Many types of problems arise:
sediment decreases the storage capacity of lakes
and reservoirs, clogs streams and drainage
channels, causes deterioration of aquatic hab-
itats, increases water treatment costs, and car-
ries displaced plant nutrients.

Illinois Erosion Control Program

In response to the accelerated loss of soil
productivity and to the off-the-farm effects of
erosion, the state of Illinois has designed an
erosion control program. The goal of this pro-
gram is to reduce annual soil erosion losses on
all agricultural land to one to five tons per acre
by the year 2000 depending upon the soil type.
This rate of erosion is considered the soil loss
tolerance level (the T value). Where erosion
exceeds the T value, soil is being lost so fast that
the land's natural productivity is being dimin-
ished. Table 1 lists the T value for most Illinois
soils (all tables are given at the end of the text).

The erosion control program is divided into
intermediate goals, all leading up to the year
2000. To begin the program, the 98 soil and
water conservation districts in Illinois devel-
oped soil erosion standards for all soils in their
districts. The districts' standards, which went
into effect on January 1, 1983, were required to
be at least as stringent as the state's guidelines,
although some districts developed standards
stricter than the state's guidelines.

The state's guidelines are as follows:

• By January 1, 1983, erosion on all farmland
could not exceed four times the T value (4 to
20 tons per acre annually) established for
the soil type.

• By January 1, 1988, soil loss cannot exceed
two times the T value (2 to 10 tons per acre
annually). Where conservation tillage would
solve the erosion problem and the slope is
less than five percent, however, soil loss
must not exceed the T value (1 to 5 tons per
acre annually).

• By January 1 , 1 994, erosion on all farmland
cannot exceed one and a half times T (V/, to
1% tons per acre annually).

• By January 1 of the year 2000, erosion
cannot exceed the T value (1 to 5 tons per
acre annually) on any Illinois farmland.

Although the soil and water conservation dis-
tricts are delegated the task of administrating
the erosion control program, it is, as of November,
1983, still voluntary. There is, however, a clearly
defined complaint process. It is always possible
that the program will become mandatory if the
voluntary approach does not work.

The Universal Soil Loss
Equation (USLE)

The Universal Soil Loss Equation (USLE)
provides a convenient way for you to estimate
the rate of soil loss on your land so that you can
see how that rate compares with your district's
standards. The USLE takes into account the
major factors that influence soil erosion by rain-
fall: rainfall patterns, soil types, slope steepness,
and management and conservation practices. It
was developed by the Agricultural Research
Service, the state experiment stations, and the
Soil Conservation Service (SCS), using research
data from many research stations, including
work at Dixon Springs, Urbana, and Elwood,
Illinois. More than 10,000 plot years of data
were analyzed and used to develop the equation
in the early 1960s. Additional data, mainly from
rainfall simulator plots, have been added to the
equation in the latest revision. Most of the
recent data covers conservation tillage, reduced
tillage, till-plant, and no-till systems.

The USLE represents the average annual
rate of soil loss due to splash, sheet, and rill
erosion. It does not estimate soil erosion from
gullies or stream banks or the amount of sedi-
ment reaching streams. Moreover, the equation
only gives the estimated average annual splash,
sheet, and rill erosion for the specific field
segment for which you have determined the
appropriate factors. It will not reflect the aver-
age soil erosion rate for the entire field unless

the segment you chose represents the field. In
general, however, you should not select a "repre-
sentative" field segment, but the field segment
where erosion is generally more severe. Taking
estimates on several field segments will give
you a better idea of the scope of your erosion
problems. However, do not take an average of
the several estimates because that may mask
the severity of erosion on a particular segment.
The equation is simple to use. Once you have
determined the values for each of the five factors,
you multiply them using a pocket calculator or,
if you prefer, pencil and paper. The equation is:

RXKXLSXCXP = A

where R — rainfall factor

K = soil erodibility factor
LS = length and steepness of slope factor
C = cropping and management factor
P = conservation practices factor
A = the computed average annual soil ero-
sion loss in tons per acre

Once you have determined A, you can com-
pare it with the T values in Table 1 and with
your Soil and Water Conservation District's
standards. You also can use the equation to
evaluate the effect that various changes in your
farming practices would have on your soil loss
rate. Keep in mind, however, that A is only as
accurate as the values that you have chosen for
the five factors. In general, if you have used
reasonable care in selecting the factors, A should
be within a range of plus or minus 20 percent of
your actual average annual erosion on the field
segment.

Rainfall (R) Factor

R represents the erosion potential inherent in
the rainfall patterns of a particular area. The
factors were developed from U.S. weather data
taken at many different locations in the eastern
United States over a 22-year period. The erosive
potential of rainstorms increases as one moves
from northeastern Illinois to extreme southern
Illinois. See Figure 1 for the R value in your area.

Soil Erodibility (K) Factor

K reflects the fact that various soils erode at
different rates because of different physical
characteristics such as texture, structure, or-
ganic matter content, and soil depth. K values
for Illinois range from a low of 0.15 on sandy
soils to a high of 0.43 on highly erosive soils.

If you have a detailed soil map of your farm,
find the soil type for the specific field segment or

segments that you have chosen, and determine
the K value from Table 1. Soil maps are avail-
able for about one-half of all Illinois counties,
and many individual farm soil maps have been
prepared for counties without published soil
surveys. Check with your SCS district conserva-
tionist about any maps for your farm.

If a detailed soil map is not available, your
district conservationist can help you determine
the proper K value, or you may use Table 2 until
more accurate information is available. Table 2
allows you to determine rough K values from
your judgment of the soil's color and permeabil-
ity. Most Illinois soils with an erosion problem
will have K values of 0.28, 0.32, 0.37, or 0.43.

Area using
"R" factor
160

Area using
"R" factor
180

Area using
"R" factor
200

Area using
"R" factor
220

Figure 1. Rainfall (R) values.

Slope Length and Steepness (LS) Factor

LS represents the erosive potential of a par-
ticular combination of slope length and slope
steepness. Slope length is not the distance from
the highest point in the field to the lowest point.
To determine slope length, you must walk the
field and determine where water will flow. Dis-
regard contour farming channels and concen-
trate on natural flow patterns. Once you have
identified the natural flow patterns, determine
the point on the slope where the flow begins. The
slope length is then the distance from this point
to the point where (1) the slope gradient de-
creases enough that sediment deposition gener-
ally occurs, or (2) the runoff water becomes a
concentrated flow, or (3) the runoff enters a well-
defined channel, for example, part of a natural
drainage network or a constructed grass water-
way or terrace channel.* There is a tendency to
overestimate slope length. Slope lengths will
seldom be above 400 feet long on gentle slopes
and will usually be shorter on steeper slopes.

Slope steepness is expressed as a percentage.
The percentage of slope is the change in eleva-
tion between two points divided by the hori-
zontal distance between the two points times
100. For example, if the elevation change is 6
feet in a horizontal distance of 1 20 feet, the slope
has a 5 percent grade (6 ^ 120 X 100 = 5). Per-
cent slope can be determined with an engineer's
level, a hand level, a line or string level, or a
sighting board slope finder like the one on page
19 (instructions for using it are on page 17).

Once you have determined slope length and
steepness, you can find the LS value in Table 3.
Please note that slope classifications given in
detailed soil maps should not be used; they are
too general. The slope length and steepness
must be determined on the specific segment of
the field where you are estimating soil loss, and
the LS value must be derived from Table 3.

Cropping and Management (C) Factor

C reflects the reduction in soil erosion that
will result from growing a crop as compared
with leaving the land fallow. The amount of

*Where terraces are installed, the slope length is
usually the distance from the top of the terrace ridge
to the center of the next lower terrace channel. If the
terraces are built on the contour and used in conjunc-
tion with contour farming or contour strip cropping,
an additional P factor is used. See pages 5-6 for
calculating the P factor for terraces built on contour.

reduction depends upon the type of crop grown,
the cropping system, tillage practices, crop yield,
and residue management. Cropping and man-
agement practices influence erosion potential
by the degree to which their combinations keep
the soil surface rough or covered with crop
residues or vegetation. C values range from a
high of 1.0 for continuous fallow (soil tilled to
permit no vegetation to grow) to a low of 0.003
for excellent grass cover. By determining R X
K X LS for the field segment under examination
and multiplying that figure by various C values,
you can compare the soil erosion that you could
expect from different cropping and manage-
ment practices (without the use of soil conserva-
tion practices).

There are many possible cropping and man-
agement combinations. For example, almost
any crop can be grown continuously or in
rotation with other crops, and additional soil
protection can be gained by seeding a cover crop
in the row crop late in the season. Soils can be
left rough with considerable storage capacity, or
they can be smoothed by secondary tillage. Crop
residues can be removed, left on the soil surface,
incorporated near the soil surface, or plowed
under. Even if crop residue is left on the surface,
it can be chopped or allowed to remain as it was
after harvest.

So that C values would more accurately reflect
these and many other possible combinations
according to geographical differences in cli-
mate, planting dates, and cropping systems,
Illinois was divided into three sections. Figure 2
shows the three geographical divisions. By lo-
cating your county, you can determine which
geographically specific table to use to find your
C value. If you are in Knox County, for example.
Figure 2 tells you to see Table 4.

Northern Illinois C values can be found in
Table 4, those for central Illinois in Table 5, and
those for southern Illinois in Table 6. If you wish
to make soil erosion estimates for permanent
pasture and grazed or burned woodland, use
Table 7 for the appropriate value. Table 8 can be
used to find C values for undisturbed forest.

Once you have identified the table to use,
identify in column 1 of the table the cropping
sequence being used on the field segment being
evaluated. (Note that C values for double-crop-
ping sequences also are listed in the central and
southern Illinois tables.) If the rotation includes
soybeans, locate the row width in column 2.

The C value can now be found in the subse-
quent columns depending upon the type of

Northern
Illinois Area
Use Table 4

Central
Illinois Area
Use Table 5

Southern
Illinois Area
Use Table 6

Figure 2. Cropping and management (C) factor map.

tillage that is used — conventional, reduced, or
no-till. (Each table also lists C values for some
more common combinations of these tillage
systems. See your SCS district conservationist
if you are using other combinations.) Conven-
tional tillage includes moldboard plowing, disk-
ing, planting, and cultivating. Reduced tillage
includes either a chisel plow or a disk as the
primary tillage tool, followed by a field culti-
vator or other secondary tillage tools that leave
a portion of the crop residue on the soil surface
after planting. No-till involves leaving the soil
surface nearly undisturbed and all crop residue
on the soil surface, thus providing maximum
soil erosion protection all season.

If you are using conventional tillage, you can
look under either the "fall plow" or "spring
plow" column to determine your C value. If you
are using a reduced tillage or no-till system,
however, you will first need to determine the
percentage of residue cover after planting before
finding your C value.

Residue soil surface cover after planting is
important because it provides soil protection
when the soil would otherwise be most vulner-
able to erosion: from seedbed preparation until
new crop growth provides soil cover. This time
period, when the ground is exposed to the ele-
ments, is also when the most intensive rains
usually occur.

There is a difference in the amount of residue
cover left on the soil surface by different crops
and how well this cover holds up under planting
operations. For example, a good field of corn
with a yield of over 100 bushels per acre will
leave about 90 to 95 percent of the soil surface
covered after harvest, while a good field of
soybeans with a yield of 40 to 45 bushels per acre
will leave about 80 to 85 percent. Because soy-
bean residue is more fragile, additional tillage
or travel over the field after harvest and during
planting will cover much more of the soybean
residue than the corn residue.

To estimate the percentage of soil surface still
covered by residue after planting, you can use
the point and line method. You can make your
own line, use any line, rope, or measuring tape
that has 100 evenly spaced points, or buy a
commercially made line. To make your own line,
take a piece of 1/8- or 3/16-inch nylon rope,
about 70 feet long, and tie 100 knots, 6 inches
apart. After the knots are tied, the rope should
shorten to just about 50 feet long.

Next, make a short loop at each end of the
rope and tie the ends to stakes. Then stretch the
line across the crop rows at approximately 45
degrees. The angle or position of the rope should
be adjusted so that both stakes are placed on a
row (see Figure 3, insert).

Standing over the rope and looking straight
down at the knots, count the knots that intersect
a piece of crop residue (Figure 3). Ignore small
pieces of residue that will decay quickly or that
are too small to intersect a raindrop. Even
though stones will intersect raindrops, do not
count them. The number of knots that intersect
a piece of crop residue equals the percentage of
soil surface covered. For example, if 75 knots
intersect residue, then the surface cover is 75
percent. Make a count on three other randomly

selected areas in the field segment, and take an
average of the four areas.

Once you have determined the percentage of
soil surface covered, you can directly find the
appropriate C value in the table if you are
planting continuous corn or soybeans. Round
percentages to the nearest number of the col-
umn. If you are rotating crops, you will need to
estimate the average percentage of soil cover to
determine which column to use. For example, if
residue covered 20 percent of the soil surface
after corn was planted under a reduced tillage
system and 40 percent after soybeans were
planted, you would find your C value in the 30
percent column (20 + 40 ^ 2 = 30).

Please note that certain assumptions have
been made about the level of management, the
rotation sequence, and the tillage methods in
order to determine C values. These assumptions
are detailed in the footnotes to each table.
Therefore, you should take special care to read
the footnotes to make sure your practices and
the table's assumptions are the same. Each
footnote will give you instructions about what to
do if your practices are not the same as the
assumptions. Usually the footnote will instruct
you to multiply the value in the table by another
number to arrive at a C value that reflects your
individual practices. For example, as the gen-
eral note to Tables 4, 5, and 6 explains, all C
values in the tables assume that the field seg-
ment being evaluated is under a high level of
management with corn yields exceeding 100

bushels per acre; soybeans, 40 bushels; wheat,
45 bushels; oats, 60 bushels; and hay, 3 tons per
acre. The note instructs you to multiply the C
value in the table by 1.2 if the section is under a
medium level of management with lower yields.
Also please note that it is impossible to
predict all the individual variations in cropping
and management practices. If you cannot find
your exact practices in the appropriate table,
consult with your SCS district conservationist
or county Extension adviser about how you
might arrive at a reasonable value.

Conservation Practices (P) Factor

P represents the reduction in soil erosion
resulting from the use of conservation practices
that change the flow of runoff water, such as
contour farming, contour strip cropping, and
terracing. RxKXLSXCX Pthus equals the
soil erosion for a field segment with conserva-
tion practices applied.

The P factors for contour farming and contour
strip cropping are shown in Table 9. Because
contouring loses its effectiveness as slope length
increases, the table also gives the maximum
slope length on which contour farming is effec-
tive. Remember that contouring benefits are
obtained only when the field is relatively free
from gullies and depressions other than grassed
waterways.

When terraces are built on the contour and
used in combination with contour farming or

Figure 3. Overview (insert) and closeup of the point-and-line method of determining percentage of surface residue covering.

contour strip cropping, you must use Tables 9
and 10 in conjunction to determine your P value.
(P values are not used when terraces are not
built on the contour. Parallel terrace systems
may not meet the contour criteria.) After choos-
ing values from both tables, you multiply these
values to arrive at the correct P value.

For example, assume that you have installed
level ridge tile outlet terraces on the contour, 120
feet apart, on a 5 percent slope, and contour
farmed. From Table 9 you would determine that
the contour factor is 0.5, while from Table 10
you would determine that the terrace factor is
0.6. You would then multiply the two factors to
arrive at a conservation practices (P) value of
0.3 (0.5 X 0.6 = 0.3). This is the value that you
would insert into the USLE to determine the
annual soil erosion rate.

Research has shown that trapped sediment
accumulates in the terrace channel and ridge
area to such an extent that this portion of the
land does not deteriorate significantly. The P
factor is proportioned to give credit where the
soil resource is maintained, that is, the factor
gets larger as the terrace interval gets wider,
thus giving less credit. Tile outlet terraces are
more effective in trapping sediment than open
outlets, and trapping efficiency goes down as
terrace grade increases.

Using the USLE

Working through Some Examples

How the land's physical features, the climate,
your crops, and your soil conservation practices
affect soil losses has been briefly discussed. The
USLE enables you to estimate your average
annual soil erosion losses for a cropping and
management system by multiplying all the
values assigned to factors that affect erosion.
Two examples of how to use the equation follow.

Example 1. Our first example assumes a farm
in Pike County, Illinois, with Fayette silt-loam
soil. The field segment is on a 5 percent slope
that is 300 feet long. The R value for Pike County
is 200 (Figure 1); the K value for Fayette silt-
loam is 0.37 (Table 1); the LS value is 0.93 (Table
3). The amount of soil lost annually under fallow
would thus be:

R K LS A

200 X 0.37 X 0.93 = 68.8 tons

Figure 2 indicates that the C values for Pike
County can be found in Table 5. The crop

rotation used is corn, soybeans, wheat, and a
clover catch crop. The field is conventionally
tilled and spring plowed. Residues are left on the
soil surface, and soybeans are drilled in 10-inch
rows. The field segment is under a high level of
management. According to Table 5, therefore,
the C factor is 0.22. (Note that footnote / indi-
cates to use the same C factor with or without
legume seeding.) We can now determine the
annual soil erosion loss that would occur if the
farm did not use conservation practices (P value):

C A

R X K X LS = 68.8 X 0.22 = 15 tons

If the field is contour farmed, a P factor of 0.5
(Table 9) would be multiplied by the above value
to determine A. As a result, the amount of soil
lost annually would be:

P A

R X K X LS X C = 15 X 0.5 = 7.6 tons

Because the soil loss tolerance level is 5 tons
per acre for a Fayette silt-loam soil that has
more than three inches of topsoil (Table 1), 7.6
tons per acre is well above the limit.

If the tillage system were changed to a reduced
tillage system that used primary tillage and two
secondary operations prior to planting, A would
be significantly lower. Let us assume that this
reduced tillage system resulted in an average
percentage of soil cover of 40 percent (the aver-
age of the percent residue cover after corn was
planted and after soybeans were planted). The C
value, according to Table 5, would change to
0.12. As a result, A would reduce to:

R K LS C P A

200 X 0.37 X 0.93 X 0.12 X 0.5 = 4.1 tons

Thus, this particular cropping and manage-
ment system would bring the average annual
soil erosion below the 5-ton soil erosion limit.
Other conservation options include terracing
the field, changing the crop rotation, using zero
till, or using a combination of practices.

Example 2, As a second example, let us assume
a farm in Perry County with a field segment of
Ava silt loam soil and a 5 percent slope that is
200 feet long. The R value for Perry County is
220 (Figure 1); the K value for silt loam is 0.43
(Table 1); the LS value is 0.76 (Table 3). The T
value for this soil is 4 tons per acre (Table 1). The
calculation below gives the annual soil loss
under fallow:

R K LS

220 X 0.43 X 0.76

A
71.9 tons

Figure 2 indicates that the C value for Perry
County can be found in Table 6. On this seg-
ment, a corn and soybean rotation is grown
conventionally tilled and spring plowed. Both
crops are planted in 30-inch rows. The field
segment is under a medium level of manage-
ment with corn yields of 75 bushels per acre and
soybean yields of 33 bushels per acre.

According to the spring plow column in Table
6, therefore, the C value is 0.31. However, the
general note to the entire table indicates that the
value in the table must be multiplied by 1.2
when the field is under a medium level of
management. The C value for the field segment
in this example is thus actually 0.37 (0.31 X 1.2).
As a result, 26.6 tons of soil would be lost
annually without any conservation practices:

C A

R X K X LS = 71.9 X 0.37 = 26.6 tons

If the field is contour plowed, a P factor of 0.5
(Table 9) would be multiplied by the above value
to determine A under conservation practices:

P A

26.6 X 0.5 = 13.3 tons

This value is substantially above the T value of
4. The farmer would thus probably have to
change several practices to lower the value.

Perhaps the operator would consider chang-
ing to a no-till system. But would such a change
lower the soil loss to the established T value? A
quick answer can be obtained by looking at the
C value for a no-till corn-soybean rotation.
Assuming that such a no-till rotation would
achieve an average of 50 percent soil cover after
planting, the C value would be 0.11. However, if
the operator still plans a medium level of man-
agement, the C value actually would be 0.13
(0.11 X 1.2). As the calculation below indicates,
a no-till system would substantially reduce the
field's annual soil loss, nearly meeting the T
value and long-term state goals:

R K LS C P A

220 X 0.43 X 0.76 X 0.13 X 0.5 = 4.6 tons

Increasing the crop yield to meet the high level
of management would lower the soil loss to
below the T value:

R K LS C P A

220 X 0.43 X 0.76 X 0.11 X 0.5 = 3.95 tons

Of course, other options exist. The operator
could change the rotation (corn and double-crop,
no-till wheat and soybeans, for example, would
result in a C value of 0.08), use a combination

tillage system, terrace on the contour, or plant
narrow-row soybeans, to name a few.

As both these examples suggest, the use of the
USLE is not just limited to determining the
nearness of your soil loss to the T value. The
USLE also can be used to evaluate the effects of
your management decisions on the soil erosion
on your farm.

Solving the USLE for C

Let us assume that you have determined your
annual rate of soil loss using the USLE and
found that the rate is above the T value for your
soil type. If you do not have the option of
changing or adding conservation practices (P
value), you will want to know what particular
cropping and management practices (C value)
would lower your annual rate to or below the T
value. To solve the USLE for C, use the follow-
ing formula:

R X K X LS X P

Using the information from Example 1, we
could solve for an acceptable C factor:

5 5

200 X 0.37 X 0.93 X 0.5

34.4

= 0.14

After solving this equation, we would know
that any crop rotation and tillage system in
Table 5 with a Cfactorof 0.14 or less would help
us meet the annual soil erosion goal in that
example of 5 tons per acre.

Getting Help

The Soil Conservation Service (SCS) district
conservationist located in each of the soil and
water conservation district offices has for many
years used this method of estimating soil ero-
sion losses. Therefore, you may wish to have an
SCS representative assist you in determining
the appropriate factors to insert into the USLE.
The district conservationist can also help you
by recommending alternative soil erosion con-
trol practices. In addition, the SCS conserva-
tionist can supply you with C values for com-
binations of tillage systems for a rotation.

8

Table 1. Soil Erodlbllity (K) and Tolerance (T) Values for Specific Illinois Soils

K

T

K

T

K

T

Soil type

factor

factor*

Soil type

factor

factor*

Soil type

factor

factor*

Ade98

0.17

5-5

Brooklyn 136

0.37

4

Drummer 152

0.28

5

Alford 308

.37

5-4

Bryce 235

.28

3

Drury 75

.37

5

Allison 306

.28

5

Burkhardt 961

.20

3-2

Dubuque 29

.37

4-3

Alvin 131

.24

5-4

Burnside 427

.37

4

Dunbarton 505

.37

2-1

Ambraw 302

.28

5

Cairo 590

.28

4

Du Page 321

.28

5

Andres 293

.28

5-4

Calamine 746

.28

5

Dupo 180

.37

5

Aptakisic 365

.37

5-4

Calco 400

.28

5

Durand 416

.32

5-4

Arenzville 78

.37

5

Camden 134

.37

5-4

Ebbert 48

.37

5

Argyle 227

.32

4-3

Canisteo 347

.28

5

Edgington 272

.32

5

Armiesburg 597

.28

5

Cape 422

.32

3

Edinburg 249

.37

4

Ashdale411

.32

5-4

Carmi 286

.20

4-3

Edmund 769

.32

2-1

Ashkum 232

.28

5

Casco 323

.32

3-2

Elburn 198

.28

5

Assumption 259

.32

4-3

Catlin 171

.32

5-4

Elcoll9

.37

4-3

Atkinson 661

.28

4-3

Channahon 315

.37

2-1

El Dara 264

.24

5-4

Atlas 7

.43

3-2

Chats worth 241

.43

3-2

Eleroy 547

.37

4-3

Atterberry 61

.32

5-4

Chauncey 287

.37

3

Elkhart 567

.32

5-4

Ava 14

.43

4-3

Chelsea 779

.17

5

ElHott 146

.28

4-3

Backbone 768

.24

4-3

Chute 282

.15

5

ElHson 137

.37

4-3

Banlic 787

.43

4

Cisne 2

.37

3

Elsah 475

.37

3

Harrington 443

.32

5-4

Clarence 147

.37

3-2

Emma 469

.37

5-4

Batavia 105

.32

5-4

Clarksdale 257

.37

5-4

Faxon 516

.28

4

Baxter 599

.32

4-3

Clarksville 471

.24

2-1

Fayette 280

.37

5-4

Baylis 472

.37

4-3

CHnton 18

.37

5-4

Fieldon 380

.28

5

Beardstown 188

.32

5-4

Coatsburg 660

.37

3-2

Fincastle 496

.37

5-4

Beasley 691

.43

3

Coffeen 428

.32

5

Fishhook 6

.43

3-2

Beaucoup 70

.32

5

Colo 402

.28

5

Flagg 419

.37

5-4

Bedford 598

.43

4-3

Colp 122

.43

3-2

Flagler 783

.20

4-3

Beecher 298

.37

3

Comfrey 776

.28

5

Flanagan 154

.28

5

Belknap 382

.37

5

Corwin 495

.32

5

Fox 327

.37

4-3

Berks 955 & 986"

.28

3-2

Cowden 112

.37

3

Frankfort 320

.37

3-2

Billett 332

.20

5-4

Coyne 764

.20

5-4

Friesland 781

.20

5-4

Birds 334

.43

5

Creal 337

.37

5-4

Frondorf 786

.32

3-2

Birkbeck 233

.37

5-4

Dakota 379

.28

4-3

Gale 413

.37

4-3

Blackoar 603

.28

5

Dana 56

.32

5-4

Genesee 431

.37

5

Blair 5

.43

3-2

Darmstadt 620

.43

3

Gilford 201

.20

5

Bloomfield 53

.15

5

Darroch 740

.28

5

Ginat 460

.43

4

Blount 23

.43

3-2

Darwin 71

.28

3

Gorham 162

.32

5

Bluford 13

.43

3-2

Del Rey 192

.43

3-2

Gosport 551

.43

3-2

Bodine 471

.24

2-1

Denny 45

.37

3

Goss 606

.24

2-1

Bold 35

.43

5-4

Denrock 262

.37

3-2

Granby 513

.17

5

Bonfield 493

.24

3

Derinda 417

.43

3-2

Grantsburg 301

.43

4-3

Bonnie 108

.43

5

Dickinson 87

.20

4-3

Grays 698

.32

5-4

Booker 457

.37

5

Disco 266

.20

4

Grellton 780

.24

5-4

Boone 397

.15

4

Dodge 24

.37

4-3

Griswold 363

.32

5-4

Bowdre 589

.28

4

Dodgeville 40

.32

4-3

Hamburg 30

.43

5

Bowes 792

.32

5-4

Dorchester 239

.37

5

Harco 484

.32

5

Boyer 706

.17

4-3

Douglas 128

.32

5-4

Harpster 67

.28

5

Brandon 956"

.37

3-2

Dowagiac 346

.28

4-3

Harrison 127

.32

5-4

Brenton 149

.28

5

Downs 386

.32

5-4

Hartsburg 244

.28

5

Broadwell 684

0.32

5-4

Dresden 325

0.28

4-3

Harvard 344

0.32

5-4

Source: Illinois Technical Guide, Section 2, Soil Conservation Service, Champaign, Illinois.

^The first number in the column applies to soils with no erosion to moderate erosion; the second number, where it appears, applies to

seriously eroded land with three inches or less topsoil remaining.

''In complexes with other soils.

Table 1. Continued

K

T

K

T

K

T

Soil type

factor

factor^

Soil type

factor

factor'

Soil type

factor

factor'

Hayfield 771

0.32

5

Lorenzo 318

0.28

3-2

Ockley 387

0.37

5-4

Haymond 331

.37

5

Lukin 167

.37

4-3

Oconee 113

.37

3-2

Hennepin 25

.32

5-4

Marissa 176

.37

4

Octagon 656

.32

5-4

Herbert 62

.32

5

Markham 531

.37

3-2

Odell 490

.32

5-4

Herrick 46

.28

5

Markland 467

.43

3-2

Ogle 412

.28

5-4

Hesch 390

.20

4-3

Marseilles 549

.37

4-3

Okaw 84

.43

3-2

Hickory 8

.37

5-4

Marshan 772

.28

4

Onarga 150

.20

4-3

High Gap 556

.37

4-3

Martinsville 570

.37

5-4

Oneco 752

.32

5-4

Hitt 506

.32

5-4

Martinton 189

.32

4-3

Orio 200

.28

4

Homer 326

.37

4

Massbach 753

.32

4-3

Orion 415

.28

5

Hononegah 354

.15

4

Matherton 342

.20

4-3

Otter 76

.28

5

Hoopeston 172

.20

4

Maumee 89

.17

5

Palsgrove 429

.32

4-3

Hosmer 214

.43

4-3

McFain 248

.28

4

Pana 256

.32

4-3

Hoyleton 3

.37

3-2

McGary 173

.43

3-2

Papineau 42

.20

4

Huey 120

.43

2

McHenry 310

.37

5-4

Parkville 619

.28

5

Huntington 600

.28

5

Medway 682

.32

5

Parr 221

.32

5-4

Huntsville 77

.28

5

Metea 205

.17

5-4

Patton 142

.28

5

Hurst 338

.43

3-2

Miami 27

.37

5-4

Pecatonica 21

.37

5-4

lona 307

.37

5-4

Middletown 685

.37

5-4

Pella 153

.28

5

Ipava 43

.28

5

Milford 69

.28

5

Peotone 330

.28

5

Iva 454

.43

4-3

Millbrook 219

.32

5-4

Petrolia 288

.32

4

Jacob 85

.28

3

Millington 82

.28

5

Piasa 474

.37

3

Jasper 440

.28

5

Millsdale317

.32

4

Pike 583

.37

5-4

Joliet 314

.28

3

Milroy 187

.24

4

Pillot 159

.32

4-3

Joslin 763

.32

5-4

Mokena 295

.28

4-3

Piopolis 420

.43

4

Joy 275

.28

5-4

Mona 448

.28

4-3

Plainfield 54

.17

5

Jules 28

.37

5

Monee 229

.37

3-2

Piano 199

.32

5-4

Juneau 782

.37

5

Montgomery 465

.37

5

Plattville 240

.32

5-4

Kane 343

.28

4

Montmorenci 57

.32

5-4

Port Byron 277

.32

5-4

Kankakee 494

.20

4

Morley 194

.43

3-2

Proctor 148

.32

5-4

Karnak 426

.32

3

Morocco 501

.17

5

Racoon 109

.43

3

Keller 470

.37

3-2

Mt. Carroll 268

.32

5-4

Raddle 430

.32

5-4

Keltner 546

.32

4-3

Mundelein 442

.28

5-4

Radford 74

.28

5

Kendall 242

.37

5-4

Muren 453

.37

5-4

Rantoul 238

.28

3

Keomah 17

.37

5

Muscatine 41

.28

5

Raub 481

.28

5

Kernan 554

.37

4-3

Muskingum 425

.28

3-2

Reddick 594

.28

5

Kidder 361

.32

5-4

Myrtle 414

.32

5-4

Reesville 723

.37

5

Knight 191

.32

4

Nappanee 228

.43

3-2

Richview 4

.32

5-4

La Hogue 102

.28

5

Nasset 731

.32

4-3

Ridgeville 151

.20

4

Lamont 175

.24

5-4

Negley 585

.32

3-2

Ridott 743

.32

4-3

Landes 304

.20

5

Neotoma 976 & 977"

.20

3-2

Riley 452

.28

4

La Rose 60

.32

5-4

Newberry 217

.37

3

Ringwood 297

.28

5-4

Lawler 647

.28

4

New Glarus 928 &

Ripon 324

.32

4-3

Lawndale 683

.32

5

561"

.37

4-3

Ritchey 311

.37

2-1

Lawson 451
Lax 628

.28
.43

5
4-3

Niota 261
Oakville 741

.37
0.15

3
5

Robbs 335
Roby 184

.43
.24

4-3
4

Lisbon 59

.28

5-4

Rockton 503

.28

4-3

Littleton 81

.28

5

Rodman 93

.20

3-2

Lomax 265

.28

5

Romeo 316

0.37

1

Loran 572

0.28

4-3

""The first number in the column applies to soils with no erosion to moderate erosion; the second number, where it appears, applies to
seriously eroded land with three inches or less topsoil remaining.
''In complexes with other soils.

10

Table 1. Continued

K

T

K

T

K

T

Soil type

factor

factor"

Soil type

factor

factor'

Soil type

factor

factor"

Ross 73

0.32

5

Strawn 224

0.37

4-3

Washtenaw 296

0.37

5

Rowe 230

.28

5

Streator 435

.28

3

Watseka 49

.17

2

Rozetta 279

.37

5-4

Stronghurst 278

.37

5-4

Wauconda 697

.32

4-3

Ruark 178

.24

4

Sunbury 234

.32

5-4

Waukee 727

.24

4-3

Rush 791

.37

5-4

Swygert 91

.43

3-2

Waukegan 564

.32

4-3

Rushville 16

.43

3

Sylvan 19

.37

5-4

Waupecan 369

.32

4-3

Russell 322

.37

5-4

Symerton 294

.32

5-4

Wea 398

.32

5-4

Rutland 375

.32

5-4

Tallula 34

.32

5-4

Weinbach 461

.43

4-3

Sabina 236

.37

5-4

Tama 36

.32

5-4

Weir 165

.43

4

Sable 68

.28

5

Tamalco 581

.43

3-2

Wellston 339

.37

4-3

Saffell 956"

.20

4

Tell 565

.37

4-3

Wenona 388

.32

4-3

Sarpy 92

.15

5

Terril 587

.24

5

Wesley 141

.24

3-2

Saude 774

.28

4-3

Thebes 212

.37

4-3

Westland 300

.28

5

Sawmill 107

.28

5

Thorp 206

.37

4

Westmore 940"

.37

4

Saybrook 145

.32

5-4

Tice 284

.32

4

Westville 22

.37

5-4

Saylesville 370

.37

3-2

Timula 271

.37

5-4

Whalan 509

.32

4-3

Schapville 418

.32

3-2

Titus 404

.32

4

WheeHng 463

.32

4-3

Sciotoville 462

.37

4-3

Toronto 353

.32

5-4

Whitson 116

.43

4

Seaton 274

.37

5-4

Traer 633

.37

5

Will 329

.28

4

Selma 125

.28

5

Trempealeau 765

.28

3

Wingate 348

.32

5-4

Sexton 208

.43

4

Troxel 197

.28

5

Winnebago 728

.32

5-4

Shadeland 555

.37

4

Uniontown 482

.37

4-3

Woodbine 410

.37

4-3

Sharon 72

.37

5

Ursa 605

.37

4-3

Worthen 37

.32

5-4

Shiloh 138

.28

3

Varna 223

.32

4-3

Wynoose 12

.43

3

Shoals 424

.37

5

Velma 250

.32

4-3

Xenia 291

.37

5-4

Shullsburg 745

.32

4-3

Virden 50

.28

5

Zanesville 340

.43

3-2

Sidell 55

.32

5-4

Virgil 104

.32

5-4

Zipp 524

.28

5

Sogn 504

.28

1

Wabash 83

.28

5

Zurich 696

.37

5-4

Sparta 88

.17

5

Wagner 26

.28

3

Zwingle 576

0.43

3-2

St. Charles 243

.37

5-4

Wakeland 333

.37

5

St. Clair 560

.37

3-2

Walshville 584

.43

3-2

Starks 132

.37

5

Ware 456

.32

4

Stockland 155

.20

2-1

Warsaw 290

.28

4-3

Stonelick 665

.24

5

Wartrace 215

0.37

5-4

Stoy 164

0.43

4-3

"The first number in the column applies to soils with no erosion to moderate erosion; the second number, where it appears, applies to
seriously eroded land with three inches or less topsoil remaining.
In complexes with other soils.

Table 2. Soil Erodlbility (K) Values for Certain General Soil Types

11

Soil type

K Soil loss tolerance"

value (tons/acre/year)

Dark and moderately dark soil somewhat wet and with good perme-
ability (for example, Muscatine, Ipava, Flanagan, and Herrick) 0.28 5

Dark and moderately dark prairie soil with good permeability (for

example, Catlin, Harrison, Proctor, Saybrook, and Tama) .32 5-4

Dark and light prairie soil with restricted permeability (for example,

Cisne, Cowden, and Clarence) .37 3-2

Dark prairie soil with very restricted permeability (for example,

Swygert) .43 3-2

Light-colored forest soil with good permeability (for example, Alford,

Birkbeck, Clinton, and Fayette) .37 5-4

Light-colored forest soil with restricted permeability (for example, Ava,

Blount, Grantsburg, Hosmer, and Wynoose) .43 4-3

Sandy loam soil (for example, Dickinson, Onarga, and Ridgeville) .... .20 4-3

Loose sand (for example, Ade, Plainfield, and Sparta) 0.17 5

Note: See Table 1 for a more complete listing of K values for specific soils.

"The first number represents the soil loss tolerance for soils with less than severe soil erosion. The second number,
where it appears, represents the soil loss tolerance for soils with severe soil erosion and strong evidence of subsoil
mixing with the topsoil.

Table 3. Slope Length and Steepness (LS)

Values

for Specific Combinations of Length and Steepness

Slope
steepness

Slope length (feet)

(percent)

25

50

75

100

150 200

300

400

500

600

1 0.01 0.11 0.12 0.13 0.15 0.16 0.18 0.19 0.20 0.21

2 0.13 0.16 0.19 0.20 0.23 0.25 0.28 0.31 0.33 0.34

3 0.19 0.23 0.26 0.29 0.33 0.35 0.40 0.44 0.47 0.49

4 0.23 0.30 0.36 0.40 0.47 0.53 0.62 0.70 0.76 0.82

5 0.27 0.38 0.46 0.54 0.66 0.76 0.93 1.07 1.20 1.31

6 0.34 0.48 0.58 0.67 0.82 0.95 1.17 1.35 1.50 1.65

8 0.50 0.70 0.86 0.99 1.21 1.41 1.72 1.98 2.22 2.43

10 0.69 0.97 1.19 1.37 1.68 1.94 2.37 2.74 3.06 3.36

12 0.90 1.28 1.56 1.80 2.21 2.55 3.13 3.61 4.04 4.42

14 1.15 1.62 1.99 2.30 2.81 3.25 3.98 4.59 5.13 5.62

16 1.42 2.01 2.46 2.84 3.48 4.01 4.92 5.68 6.35 6.95

18 1.72 2.43 2.97 3.43 4.21 4.86 5.95 6.87 7.68 8.41

20 2.04 2.88 3.53 4.08 5.00 5.77 7.07 8.16 9.12 10.0

12

Table 4. Cropping and Management (C) Values

for Northern

Illinois

Soybean

row
width"

Conventional
tillage*^

Chisel, disk

20% 30%

or ridge**®

40% 50%

All corn

and

soybeans planted no-till*

Crop
sequence*

Fall
plow

Spring
plow

20% 30%

40%

50%

60%

70%

80%

90%

Continuous
soybeans

wide
narrow

.44
.36

.39
.32

.36
.31

.32
.29

.25 .20
.21 .18

.16
.15

Continuous
corn

.34

.29

.21

.18

.15

.12

.08

.06

.04

.03

C-Sb

wide

.38

.33

.28

.24

.20

.19

.18

.14

.10

.09

narrow

.34

.30

.27

.23

.19

.18

.17

.14

.10

.09

C-C-Sb

wide

.36

.32

.26

.22

.18

.17

.14

.11

.08

.07

narrow

.34

.30

.25

.21

.17

.16

.14

.11

.08

.07

C-Sb-G'

wide

.27

.25

.18

.16

.13

.12

.10

.07

.05

.04

narrow

.25

.23

.17

.15

.12

.11

.09

.07

.05

.04

C-C-G-M^*^

.14

.12

.10

.09

.08

.07

.04

.03

.02

.02

C-Sb-G-M9''

wide

.15

.13

.10

.09

.08

.08

.05

.04

.03

.03

narrow

.13

.12

.10

.09

.08

.07

.05

.04

.03

.03

C-Sb-M-Mfl-»'

wide

.12

.10

.08

.07

.06

.06

.03

.02

.02

.01

narrow

.11

.08

.07

.07

.06

.06

.03

.02

.02

.01

C-G-M9*'

.09

.07

.07

.07

.06

.06

.03

.02

.02

.01

C-M-M-Mfl*^

.05

.04

.01

.008

.006

.006

Combination Tillage Systems

Crop
sequence'

C-Sb

Tillage systems used for sequence

Corn after soybeans, no-till; soybeans after corn,
fall chisel, spring secondary tillage

Soybean row
width*'

wide
narrow

Percent soil cover after
planting each crop

20%

.23

.21

30%

.19

.18

40%

.15
.14

Source: C values for this table were calculated from the Soil Conservation Service's Illinois Technical Guide, Section I-C (EI Curve 14).
NOTE: Values in this table are based on high level management with yields equal to or exceeding the following: corn, 100
bushels per acre; soybeans, 40 bushels per acre; wheat, 45 bushels per acre; oats, 60 bushels per acre; meadow, 3 tons per
acre. For medium level management, multiply values by 1.2.

*In this column, C = corn, Sb = soybeans, G ~ small grain, M = meadow, and W = wheat.

"Use the wide-row values for soybean rows wider than 20 inches. Use the narrow-row values for soybean rows planted 20
inches or less, including drilled.

''Where corn residue is removed for silage or other purposes, multiply the C value by 1.2 for intensive rotations such as
corn and soybeans or corn, corn, and soybeans. Do not multiply the C value by any number for the less intensive
rotations, including meadow crops, where crop residue is removed.

"Values for chisel and disk systems are for aSi primary tillage and two secondary tillage operations prior to planting. For
primary tillage in the spring or ridge planting up and down hill, multiply the appropriate C values by 0.9 in northern
Illinois, by 0.8 in central Illinois, and by 0.7 in southern Illinois. For ridge planting on the contour, multiply the
appropriate C value by 0.7 in northern Illinois, by 0.6 in central Illinois, and by 0.5 in southern Illinois. Ridge planting is
applicable only for row crops following row crops.

®The percent figures represent the percentage of the soil surface covered after planting. The percent figure for a rotation is
equal to the average cover for the crop sequence. For example, if, in a corn-soybean rotation, residue covered 20 percent of
the soil surface after corn was planted and 60 percent after soybeans were planted, the average cover would be 40 percent,
and you would find your C value in the 40 percent column.

The same C values are applicable for small grain both with and without a catch crop.

^Chisel and disk C values are calculated for spring-plow, conventional tillage when corn follows meadow.

''Values are based on a sod or grass legume mixture consisting of at least 50 percent grass and established at least one full
growing season. If meadow is primarily legume, multiply the appropriate C value by 1.2.

13

Table 5. Cropping and Management (C) Values for Central Illinois

Crop
sequence"

Soybean

row
width"

Conventional
tillage*^

Fall Spring
plow plow

Chisel, disk, or ridge**'*

20% 30% 40% 50%

All corn and soybeans planted no-till'

20% 30% 40% 50% 60% 70% 80% 90%

Continuous

soybeans wide .48 .41

narrow .40 .30

Continuous

corn .36 .29

C-Sb wide .41 .35

narrow .36 .31

C-C-Sb wide .39 .33

narrow .36 .30

C-C-Sb-G' wide .32 .26

narrow .29 .24

C-Sb-G' wide .30 .25

narrow .27 .22

C-Sb-G-Mfl'*' wide .17 .13

narrow .14 .12

C-Sb-Mfl-*' wide .19 .15

narrow .16 .13

C-C-C-M-M-Ms-*^ .10 .08

C-M-M-Ma-"^ .05 .04

.37
.31

.21

.28
.27

.26
.25

.19

.18

.18
.17

.10
.10

.11
.10

.06

.35
.30

.18

.24
.23

.22
.21

.16
.16

.15
.15

.09
.09

.10
.09

.05

15

20
19

18
18

13
13

13
12

08
08

09
09

.12

.19
.18

.16
.16

.11
.11

.11
.10

.08
.08

.08
.08

05 .05

26
20

20
16

.16
.13

.18

.17

.09 .06 .05

03

.09
.09

.05
.05

.04
.03

.13
.13

.15
.14

.09
.09

.07
.06

.04
.04

.03
.03

.01

.10
.09

.11
.10

.07
.06

.05
.05

.03
.03

.02
.02

.09
.09

.08
.08

.05
.05

.04
.03

.02
.02

.02
.02

.07
.07

.04
.04

.01 .01
.008 .008

.005 .005

Combination Tillage Systems

Crop
sequence^

C-Sb

C-C-Sb

Tillage systems used for sequence

Corn after soybeans, no-till; soybeans after corn,
fall chisel, spring secondary tillage

Corn after soybeans, no-till; corn after corn, fall
chisel, spring secondary tillage; soybeans after
corn, fall chisel, spring secondary tillage

Soybean row

Percent soil cover after
planting each crop

width"

20%

30%

40%)

wide
narrow

.22

.21

.18
.17

.14

.14

wide
narrow

.22

.21

.18
.17

.14
.14

Double-Cropping Systems

Crop
sequence' Tillage systems used for double-cropping sequence

C-W/Sb Corn, conventional tillage, fall plow; disk for wheat

and soybeans

C-W/Sb Corn, fall chisel, spring secondary tillage, 30 percent
soil cover after planting; disk for wheat and
soybeans

C-W/Sb Same as above except no-till for soybeans

C-W/Sb Corn, no-till; wheat, disk; soybeans, no-till

C-W/Sb No-till for corn, wheat, and soybeans

C value
.26

.20
.19
.11
.09

Source: C values for this table were calculated from the Soil Conservation Service's Illinois Technical Guide, Section I-C (EI Curve 16).

NOTE: The footnotes for Table 5 are the same as for Table 4. Please be sure to read all footnotes because values in this
table are based upon assumptions detailed in the footnotes and your practices could be different from these assumptions.
NOTE: Values in this table are based on high level management with yields equal to or exceeding the following: corn, 100
bushels per acre; soybeans, 40 bushels per acre; wheat, 45 bushels per acre; oats, 60 bushels per acre; meadow, 3 tons per
acre. For medium level management, multiply values by 1.2.

14

Table 6. Cropping and Management (C) Values for Southern Illinois

Soybean

row
width"

Conventional
tillage*^

Chise

20%

I, disk
30%

or ri

40%

dge"*-'

50%

All onvn nnH s

soybeans planted n

o-till*

Crop
sequence*

Fall Spring
plow plow

* *** w-.-.-. *^M.m.-»^ m.

20% 30% 40%

50%

60%

70%

80% 90%

Continuous
corn

.38 .25

.20

.18

.15

.13

.07

.05

.04 .03

Continuous
soybeans

wide
narrow

.48 .37
.42 .29

.37
.34

.36
.33

.22 .17 .13
.19 .14 .10

C-Sb

wide

.42 .31

.27

.24

.21

.20

. .14

.11

.08

narrow

.39 .28

.26

.24

.20

.19

.. .14

.11

.08

C-Sb-G'

wide

.32 .24

.18

.15

.14

.. .08

.07

.05

narrow

.30 .22

.17

.15

.14

.. .08

.07

.05

C-Sb-G-M''**

wide

.17 .13

.10

.09

.09

.08

...

.05

.04

.03

.03

narrow

.16 .12

.10

.09

.09

.08

.05

.04

.03

.03

C-C-Sb

wide

.40 .29

.26

.23

.20

.19

.. .12

.09

.07

.06

...

narrow

.38 .27

.25

.22

.19

.19

.. .12

.09

.07

.06

C-C-Mo"

.17 .11

.10

.09

.08

.08

...

.03

.02

.02

.01

C-C-M-M-M8

h

.10 .06

.06

.06

.05

.05

...

.02

.02

.01

.01

C-M-M-Mo-"

.04 .03

.01

.007

.005

.005 .

Combination Tillage Systems

Crop
sequence'

C-Sb

C-C-Sb

Tillage systems used for sequence

Corn after soybeans, no-till; soybeans after corn,
fall chisel, spring secondary tillage

Corn after soybeans, no-till; corn after corn, fall
chisel, spring secondary tillage; soybeans after
corn, fall chisel, spring secondary tillage

Soybean row

Percent soil cover after
planting each crop

width"

20%

30%

40%

wide

.20

.16

.13

narrow

.18

.15

.13

wide

.20

.17

.14

narrow

.19

.16

.13

Double-Cropping Systems

Crop
sequence' Tillage systems used for double-cropping sequence

C-W/Sb Corn, conventional tillage, spring plow; disk for wheat and soybeans

C-W/Sb Same as above except no-till for soybeans

C-W/Sb Corn, no-till, 40 percent soil cover after planting; disk for wheat;

no-till soyl)eans

C-W/Sb Same as above except no-till wheat

C-Sb-W/Sb Com, conventional tillage, spring plow; soybeans, wide-row, con-
ventional tillage, spring plow; disk for wheat and soybeans

C-Sb-W/Sb Corn, no-till, 30 percent soil cover after planting; soybeans, wide-
row, conventional tillage, spring plow; disk for wheat; no-till
soybeans

C-Sb-W/Sb Corn, no-till, 40 percent soil cover after planting; soybeans, wide-
row, no-till, 80 percent soil cover after planting; disk for wheat;
no-till soybeans

C value
.21
.19

.10
.08

.24
.18

.08

Source: C values for this table were calculated from the Soil Conservation Service's Illinois Technical Guide, Section I-C (EI Curve 19).
NOTE: The footnotes for Table 6 are the same as for Table 4. Please be sure to read all footnotes because values in this table
are based upon assumptions detailed in the footnotes and your practices could be different from these assumptions.
NOTE: Values in this table are based on high level management with yields equal to or exceeding the following: corn, 100
bushels per acre; soybeans, 40 bushels per acre; wheat, 45 bushels per acre; oats, 60 bushels per acre; meadow, 3 tons per
acre. For medium level management, multiply values by 1.2.

15

Table 7. C Values for Permanent Pasture, Range, and Idle Land

Vegetative

canopy

Ground

cover that contacts the soil surface

Type

Height"

Percent
cover"

Type'

0%

20%

40%

60%

80%

95+%

No appreciable canopy

G

0.45

0.20

0.10

0.042

0.013

0.003

W

.45

.24

.15

.091

.043

.011

Tall weeds or short
brush

20 in.

25

G

.36

.17

.09

.038

.013

.003

W

.36

.20

.13

.083

.041

.011

20

50

G

.26

.13

.07

.035

.012

.003

W

.26

.16

.11

.076

.039

.011

20

75

G

.17

.10

.06

.032

.011

.003

W

.17

.12

.09

.068

.038

.011

Appreciable brush
or bushes

6.5 ft.

25

G

.40

.18

.09

.040

.013

.003

W

.40

.22

.14

.087

.042

.011

6.5

50

G

.34

.16

.08

.038

.012

.003

W

.34

.19

.13

.082

.041

.011

6.5

75

G

.28

.14

.08

.036

.012

.003

W

.28

.17

.12

.078

.040

.011

Trees but no appreci-
able low brush

13 ft.

25

G

.42

.19

.10

.041

.013

.003

W

.42

.23

.14

.089

.042

.011

13

50

G

.39

.18

.09

.040

.013

.003

W

.39

.21

.14

.087

.042

.011

13

75

G

.36

.17

.09

.039

.012

.003

W

0.36

0.20

0.13

0.084

0.041

0.011

Note: The listed C values assume that the vegetation and mulch are randomly distributed over the entire area.

■In this table, height is not the actual height of the weeds, bushes, brush, or trees. It is the drop fall height, which is the
average distance between the lowest twig, branch, or leaf and the ground (the average distance that a drop of water
would fall unimpeded). The beneficial effects of canopy decrease as the drop fall height increases and are negligible
when the drop fall height exceeds 33 feet.

''Percent canopy cover is the portion of the total surface area that would be hidden from view by canopy from an
airplane (a bird's-eye view).

•^G indicates that the cover at surface is grass, grasslike plants, decaying compacted duff, or litter at least two inches
deep. W^indicates that the cover at surface is mostly broadleaf herbaceous plants (weeds with few lateral root networks
near the surface) or undecayed residues or both.

Table 8. C Values for Undisturbed Forest Land

Area covered by canopy

of trees and undergrowth

(percent)

Area covered by duff

at least 2 inches

deep (percent)

C value

20 to 40
45 to 70
75 to 100

40 to 70

0.006

75 to 85

0.003

90 to 100

0.0005

16

Table 9. Conservation Practices (P) Values for Contour Farming and Contour Strip Cropping

Contour farming

Contour strip cropping

Slope
percent

P value

Maximum slope
length (feet)"

P value
R-G-M-M"'

P value
R-R-G-M'''=''

Strip width
(feet)«

lto2

0.60

400

0.30

0.45

130

3 to 5

.50

300

.25

.38

100

6 to 8

.50

200

.25

.38

100

9 to 12

.60

120

.30

.45

80

13 to 16

.70

80

.35

.52

80

17 to 20

.80

60

.40

.60

60

21 to 25

0.90

50

0.45

0.68

50

"Slope length limits are based upon limited data and field observations.

''R = row crop; G = small grain; M = meadow.

*^Strip cropping is most effective when there are alternate strips and equal width of row crops and
sod crops, for example, corn-corn-wheat with meadow seeding, meadow, meadow.

**A strip cropping rotation of corn-corn-wheat-meadow is less effective.

*To accommodate widths of farm equipment, generally adjust strip width downward.

Table 10. Values Used in Determining P Values for Terraces Built
on Contour and Used in Combination with Contour
Farming and Contour Strip Cropping

Terrace interval

Closed

Open outlets with percent slope of

(feet)

outlets"

0.1-0.3

0.4-0.7

>0.8

Less than 110

0.5

0.6

0.7

1.0

110 to 140

0.6

0.7

0.8

1.0

140 to 180

0.7

0.8

0.9

1.0

180 to 225

0.8

0.8

0.9

1.0

225 to 300

0.9

0.9

1.0

1.0

300 and up

1.0

1.0

1.0

1.0

■Values for closed outlet terraces also apply to terraces with underground
outlets and to level terraces with open outlets. However, closed outlet terraces
are not normally built in Illinois because of the large amount of rainfall in
Illinois.

The channel slope is measured on the 300 feet of terrace closest to the outlet or
on the third of the total terrace length closest to the outlet, whichever distance
is less.

17

How to Make and Use a Slope Gauge

How to Make

1. Glue, tack, or tape the slope gauge
sheet (located on page 00) on a 9-inch by
12-inch board. A V,-inch plywood or %-inch
thick board works best. Also, you may want
to attach these directions to the opposite
side of the board.

2. Place a small eye screw or nail at Point
1 on the slope gauge sheet.

3. Hang a string from the eye screw or
nail. Let the bottom of the string hang 1 to 2
inches below the bottom of the board.

4. Attach a weight, such as a fish line
sinker, at the end of the string.

5. Place two small finishing nails or wire
brads at Points 2 and 3 on the slope gauge
sheet. These are the sighting pins.

How to Use

1. Keep the sighting pins in your line of
vision and aim at the point on an object or
person that is the same height from the
ground as your eyes. For example, let's as-
sume you're aiming at a person who is taller
than you. If that person's chin is the same
height from the ground as your eyes, aim
for his chin (see figure). If you're aiming at a
stick, tie a ribbon around the point on the
stick that is at your eye level; then aim at
the ribbon.

2. The person or object does not need to
be any particular distance away.

3. You can aim the slope gauge either up
or down the slope.

4. Hold the slope gauge as steady as
possible and make sure the weighted string
can swing easily across the scale.

5. After you have finished sighting, hold
the string at the point where it comes to rest
on the scale.

6. Read the percent of slope directly from
the scale and record your measurement.
You may want to take several measure-
ments on the same slope to check your
accuracy.

Slope Gauge

19

Point 1

Hang weight on a string

from this point.

Point 2

Place sighting
pin here.

^0

^0

3S

Point 3

Place sighting
pin here.

Aim

«>^

tf)

'' '' 20 IS

10 5 0 5

10 15 20 25

30

Read percent of slope directly on this scale. At the point
where string rests on scale, the number indicates
percent of slope.

35^

^84i1lll

Urbana, Illinois November, 1983

Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, DONALD L. UCHTMANN, Director, Cooperative Extension Service, University of Illinois at
Urbana-Champaign. The Illinois Cooperative Extension Service provides equal opportunities in programs and employment.

1 .5M— Rep.— 1 2-93— MO

II

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