Soil Conservation An Assessment of the National Resources Inventory, Volume 2 (1986) / Chapter Skim
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3. Field Estimates of C Factors: How Good Are They and How Do They Affect Calculations of Erosion
3. Field Estimates of C Factors: How Good Are They and How Do They Affect Calculations of Erosion
Pages 63-89
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From page 63... ...
A basic objective of the 1982 NRI was to provide data on the extent and distribution of soil erosion in the United States. As with the 1977 NRI, the USLE was used to estimate soil erosion by water.
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From page 64... ...
Soil loss ratios vary during the year with crop canopy, ground cover, primary tillage, seedbed preparation, and harvest. A value for C is a weighted ~ , soil loss ratio based on the distribution of rainfall erosivity over the year.
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From page 65... ...
65 ,1 A Ail £ Cal o o ·,, ~5 o ~4 U]
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From page 66... ...
currently provides financial assistance to farmers to adopt conservation tillage practices. Lastly, the C factor is important because it is probably the factor most in need of revision, especially in the areas of the effectiveness of crop residues in controlling erosion (Cogo et al., 1983, 1984; Laflen et al., 1981)
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From page 67... ...
Although the impact of crop residue management is included in the C factor relationship used in the 1982 and 1977 NRIs, more recent information indicates that the importance of residues in erosion control has been underestimated. C values are currently selected on the basis of tillage system, spring residue weights, and crop residue cover after planting (Laflen et al., 1981)
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From page 68... ...
First, the effect of residue cover and conservation tillage on erosion control is quite variable. Second, residue cover is more effective in controlling sheet and rill erosion than was considered in the C factors used in the 1977 and 1982 HRIs.
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From page 69... ...
Yet only 7 percent of the corn acres of those farmers and 26 percent of their soybean acres had the residue cover recommended by the SCS (Soil Conservation Service) to be categorized as conservation tillage.
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From page 70... ...
present in Walnut Gulch protects the soil from direct raindrop impact and surface runoff erosion and should be considered in erosion estimates. Conversely, although it is valuable as surface protection, the pavement allows runoff to be concentrated between pebbles, thereby increasing erosion Potential.
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From page 71... ...
in the United States (USDA, 1981)
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From page 73... ...
This seems especially true for cotton and may explain the high C values for land planted in this crop. Soils with low potential for water erosion, however, may be highly susceptible to wind erosion.
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From page 74... ...
However, wind erosion rates are much lower than water erosion rates on sloping lands. There is no apparent explanation for higher wind erosion rates under conservation tillage.
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From page 75... ...
Directing conservation practices at this land should be reflected in its C values. The change in C factor with increase in RKLS for selected land capability classes is given in Figure 5.
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From page 76... ...
76 En hi; it; s .,.
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From page 78... ...
Although Figure 5 shows that a large portion of subclass e land had a low potential for water erosion, a significant portion of the land with high erosion potential is not receiving conservation treatments. As earlier indicated, the situation varies by area.
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From page 79... ...
conservation tillage practices are not adequate on land with medium to high potential for water erosion, and (3) some C values in the 1982 NRI are unexpected and suspect.
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From page 80... ...
as expressed by the RKLS factor of the USLE for land capability subclasses I, IIe, IIIe, and IVe for MLRAs 103, 105, 134, and 136. The Effect of C Factors on Calculation of Erosion Given the the current state of knowledge about the USLE, what effect would reducing C on cropland have on the extent and degree of soil erosion by water?
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From page 81... ...
Some 7 percent of the cropland would require additional erosion control practices. Again, the situation varies considerably throughout the country (see Figure 9)
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From page 82... ...
It is clear that reducing the C factor through management practices can significantly affect soil erosion. But erosion control measures beyond conservation tillage need to be explored and promoted on the land.
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From page 83... ...
Second, conservation tillage is currently concentrated on land with low potential for erosion. Third, there is probably less crop residue management on the soil surface than recent data on the extent of conservation tillage imply.
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From page 84... ...
in the Universal Soil Loss Equation for forest conditions.
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From page 85... ...
R., 1984. Plan for revising Agriculture Handbook 537 to update the Universal Soil Loss Equation (USLE)
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From page 86... ...
The soil erosion laboratory's work and the tillage research conducted by John Laflen of the Agricultural Research Service at Ames, Iowa, certainly imply that residue is more effective in controlling erosion than USDA Agriculture Handbook No. 537 shows.
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From page 87... ...
Adding a channel factor to the USLE (Universal Soil Loss Equation) is being investigated, because of the concentrated flow erosion or ephemeral sullying common on cronland (see Barfield: Foster, this volume)
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From page 88... ...
Much work must be done to convince people to use conservation tillage as an erosion reduction measure on erodible land. But, just as a great breakthrough occurred in the use of conservation tillage when all farmers in the Corn Belt bought a chisel plow to work their soybean land, many then found they could also use it on corn stalks.
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From page 89... ...
1984. Determination of crop residue cover using scanning microdensitometry.
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