Soil Conservation Assessing the National Resources Inventory, Volume 1 (1986) / Chapter Skim
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5. Assessing Conservation Practices and Land Classification Schemes
5. Assessing Conservation Practices and Land Classification Schemes
Pages 75-94
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From page 75... ...
Many acres are treated with combinations of practices: terrace systems in conjunction with contour farming, and conservation tillage with stripcropping, for example. The 1982 NRI results support three basic conclusions regarding conservation practices that first emerged from analysis of the 1977 NRI (U.S.
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From page 76... ...
The percentage of acres treated appears relatively constant across the range of potential erosion. Practices on land with erosion potential less than 10 have probably been adopted for reasons other than erosion control, such as fuel and labor savings.
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From page 77... ...
The precise numbers generated from NRI data are the statistical summations of all acreage represented by sampling points; they should be used for further technical analyses.
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From page 78... ...
Figure 5-1 shows the variability in the degree of protection afforded by conservation tillage practices. Sixty-six percent of the 100 million acres treated with conservation tillage in 1982 had C-factor values between 0.1 and 0.30.
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From page 79... ...
Of that, about 13 percent was in conservation tillage in 1982. About 70 percent of the Cropland had an RKLS value of 10 tons/ acre~year or less, a very small potential for sheet and rill erosion.
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From page 80... ...
Department of Agriculture, Soil Conservation Service.
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From page 81... ...
Several studies based on 1977 NRI data indicated that much of the land in conservation tillage had a modest potential for sheet and rill erosion before the practice was adopted (American Farmland Trust, 1984~. Two-thirds of the land treated with conservation tillage in the Corn Belt in 1977 had an inherent sheet and rill erosion potential of less than 20 tons/acre~year, which is below the national average RKLS value of 21.7 tons/acre~year reported for all cropland.
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From page 82... ...
On lands susceptible to high rates of sheet and rill erosion, it is generally difficult and costly to devise effective conservation farming systems. Implications for Policy and Program Administration The 1982 NRI has advanced the understanding of the concentration of soil erosion and the distribution and effectiveness of soil conservation practices.
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From page 83... ...
If erosion is to be controlled, longterm land diversion programs designed to convert highly erodible cropland into stable forage- or forestry-based land uses are needed. Erosion Reduction Goals Estimates of soil erosion are imperfect indicators of actual on-farm or off-farm damage.
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From page 84... ...
The ratio of inherent erosion potential to estimates of soil loss tolerance limits proposed by the USDA Fragile Soils Work Group has the merit of recognizing the importance of including both erosion and a measure of productivity in an indicator of damage potential. At the same time, uncertainties inherent in the estimates of T values remain, and the ratios are surrogates rather than measures that attempt to capture the impact of erosion on potential productivity over time.
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From page 85... ...
Analyses of 1977 and 1982 NRI data raise questions about the utility of the LCCS for applications involving the calculation of erosion rates before or after applications of soil conservation practices. The LCCS has been used for more than 30 years; alternative schemes might be better suited to contemporary applications concerned with land erosion and conservation management.
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From page 86... ...
The NRIs provide very useful information for updating LCCS classifications and developing alternative classification schemes. Rates of Erosion: A Basis for Classification The observation that suggests a need for a new land classification scheme emerged from analysis of the distribution of erosion rates on land classified within given LCCS land classes and subclasses, which was reported by Heimlich and Bills (1986~.
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From page 87... ...
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From page 88... ...
The climatic and physical characteristics that affect sheet and rill erosion, as reflected by the RKLS product, are not homogeneous within the LCCS class IIIe nationwide. Similar variability in inherent sheet and rill erosion potentials is observed within all land capability classes and within most subclasses.
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From page 90... ...
This type of planning usually involves estimation of the sheet and rill erosion rates that would be expected before and after the use of select conservation practices. Accordingly, conservation planning generally reflects particular field conditions, regardless of the existing LCCS classifications.
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From page 91... ...
Permanent vegetative cover might be used as a conservation option on particular lands. Alternative Land Classification Schemes Enormous pressure exists today to substantially reduce federal farm program expenditures that have cost over $15 billion annually in recent years and are projected to remain over $10 billion annually throughout the next several years.
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From page 92... ...
One approach, originally advanced by the American Farmland Trust, categorizes land into one of three groups based upon progressively higher ranges of inherent potential for sheet and rill erosion (RKLS value) and proposes comparable groupings based on the potential for wind erosion.
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From page 93... ...
The committee believes that further analysis is needed to fully evaluate the suitability of alternative land classification schemes used to identify highly erodible or fragile lands, particularly in relation to policy initiatives. Improper classification of croplands could seriously undermine the effectiveness of a program initiative.
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From page 94... ...
Like the sodbuster provision, to the extent that erosion is of major concern, the eligibility criterion for placing land into a conservation reserve should employ a land classification system based on the inherent potential and actual erosion of the land rather than a land capability class and subclass designation. Classification schemes based on erosion equations are imperfect.
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