The Soils of The Regional Municipality of Ottawa=Carleton

graphic regions . Therefore, the C values for specific crops in
Ottawa-Carleton, calculated on the basis of climatic, crop
andmanagementdatafrom this region, will not necessarily be
the same ad C values for the same crops that are developed for
other areas in Ontario .
The C factor represents the components of sheet and rill
erosion which are most easily controlled or modified through
management ; whereas the given attributes of a field or area,
namely the climate (or more specifically the annual erosive
rainfall), soils and landscape are represented by the R, K and
LS components of the USLE, respectively .
Information on crop and management practices specific
to the Ottawa-Carleton region was obtained from agricultural
extension personnel . This included information on the
amount and quality of soil protection provided during and
between crops ; the type and timing of tillage operations ; and
estimated seedbed preparation, planting, and harvest dates .
The climatic information was obtained from previouslypublished
erosion indices (30) .
Basically, a C factor is the ratio between the amount of
soil eroded from a field under a specific crop and management
system to the amount of soil which would be eroded
from the same field kept in a bare, continuously fallow state .
C factor values range from 0 to 1 . A value of 1 represents a
bare, continuously-fallow condition . When this value is
applied to the rest of the equation, the soil loss calculated
form the physical attributes alone (RKLS) essentially remains
the same . However, as the value of C approaches 0, this represents
an increasingly greater reduction inthe potential erosion
due to the effects of the crop and management systems . An
extreme C value of approximately 0 would indicate that the
crop and management system has virtually eliminated the
chance of erosion occurring .
C values that are between the two extremes represent the
proportion by which the soil loss from a bare field would be
reduced under an alternative crop and/or management sys
tem . For example, a C value of 0.50 (conventional fall tillage
of silage corn following field crops, see Table 17) indicates
that this type of crop and management practice reduces the
long-term, average annual potential erosion to 50 010 of that
which would have occurred on bare soil. If all other factors
are held constant, a winter wheat crop (C = 0 .27) planted on
the same field after conventional tillage in the fall would
reduce the potential erosion to 27 076, compared to the loss
during bare soil conditions . Potential soil losses would be
reduced to 2 016 if alfalfa (C = 0.02) were present onthe field .
Generally, C values are lowest (ie . reflect good erosionreducing
potential) for crop and management systems that
cover and protect the soil for the longest period oftime, espe
cially during peak annual rainfall periods . Good crop growth,
a high percent final canopy cover, residues of plant materials
left in the soil and practices whichleave residue on the surface
alsocontribute to relatively low C values .
Table 16. LS-values for different combinations of slope length and slope gradient
Slope
Gradient
Percent 10 15 20 25 30 40
Slope Length (m)
SO 60 75 100 125 150 200 250 300
0 .2 .063 .069 .073 .076 .080 .084 .088 .091 .095 .101 .105 .109 .116 .121 .125
0 .5 .076 .083 .088 .092 .095 .101 .105 .109 .114 .121 .126 .131 .139 .145 .151
0 .8 .090 .098 .104 .108 .112 .119 .124 .129 .135 .143 .149 .155 .164 .172 .178
2 .144 .162 .177 .189 .200 .218 .233 .246 .263 .287 .307 .324 .353 .377 .399
3 .205 .232 .253 .270 .285 .311 .333 .351 .376 .410 .438 .463 .504 .539 .570
4 .256 .301 .338 .369 .397 .446 .487 .524 .573 .643 .703 .756 .849 .928 .998
5 .306 .375 .433 .485 .531 .613 .685 .751 .839 .969 1 .08 1 .19 1 .37 1 .53 1 .68
6 .385 .472 .545 .609 .667 .770 .861 .943 1 .05 1 .22 1 .36 1.49 1.72 1 .93 2.11
8 .568 .695 .803 .898 .983 1 .14 1 .27 1 .39 1 .56 1 .80 2 .01 2 .20 2 .54 2.84 3 .11
10 .784 .960 1 .11 1 .24 1 .36 1.57 1 .75 1 .92 2.15 2 .48 2 .77 3.04 3.51 3.92 4.29
12 1 .03 1.27 1 .46 1 .63 1 .79 2 .07 2 .31 2.53 2.83 3 .27 3 .65 4 .00 4 .62 5.17 5.66
14 1 .13 1.61 1.86 2.08 2.28 2 .63 2.94 3.22 3.60 4.16 4 .65 5.09 5.88 6.57 7.20
16 1 .63 1 .99 2.30 2 .57 2.82 3 .25 3 .63 3.98 4.45 5 .14 5 .75 6.30 7 .27 8.13 8.90
18 1.97 2.41 2.78 3 .11 3 .41 3.93 .4.40 4.82 5.39 6.22 6 .95 7.62 8.80 9 .83 10 .8
20 2 .34 2.86 3.30 3 .69 4 .05 4 .67 5 .22 5.72 6.40 7.39 8.26 9 .05 10.4 11 .7 12 .8