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Soil Erosion Prediction Technology for Conservation Planning George R This paper was not peer-reviewed. Pages 847-851. In: D.E. Stott, R.H. Mohtar and G.C. Steinhardt (eds). 2001. Sustaining the Global Farm. Selected papers from the 10th International Soil Conservation Organization Meeting held May 24-29, 1999 at Purdue University and the USDA-ARS National Soil Erosion Research Laboratory. Keynote: Soil Erosion Prediction Technology for Conservation Planning George R. Foster* ABSTRACT reservoirs. This reduced capacity increases flooding, reduces Soil erosion by wind, water, and tillage can cause water supply for irrigation, and hinders navigation. excessive on-site damage to landscapes and to the soil Off-site impact can be immediately adjacent to the land resources that make up landscapes and excessive damage unit where erosion produces the sediment such as fencerows to off-site resources that receive sediment produced by and drainage ditches that collect sediment from wind, water, erosion. While certain land uses, like well-maintained an tillage erosion. Or the impact can be remote in a pasture, satisfactorily control soil erosion in highly community where breathing problems occur from dust, in an erosive conditions, putting these practices on every field estuary at the outlet of a major river degraded by is impractical. Significant erosion that would ordinarily sedimentation, and at points between the origin of the occur with preferred land uses, like vegetable production sediment and its final destination. on steep slopes, can often be satisfactorily controlled with well-chosen soil conservation technology. Elements of Conservation Planning Erosion is a complex process influenced by many Conservation planning for erosion control is the variables including climate, soil, topography, and land evaluation of alternative systems according to a defined use. The potential for erosion on one farmer's field can criteria and choosing the one that best fits the situation. An be very high, while very low on a neighbor's field. acceptable conservation system must fit several Additional complexity is that soils and off-site bodies requirements. Of course, the system must protect on-site receiving sediment from upstream sources can tolerate resources, which include the landscape and the soils that varying amount of erosion without excessive damage. make up the landscape, and off-site resources, which include Erosion is not easily measured, and even if it were, air and water quality, water conveyance structures, variations in the weather require a decade or two of reservoirs, and other places where sedimentation occurs. measurements to accurately determine a long term, The conservation system must accommodate a desired average annual erosion rate at a particular site. land use, which might be crop production, recreation, or Soil erosion prediction technology has proven to be a waste disposal. The proposed system must be profitable, valuable tool for dealing with these complexities in unless supported by funding from outside sources, and fit conservation planning. Soil conservationists use this tool within the financial, managerial, and other resources to develop conservation plans that take into account the available to implement new conservation technology. For erosion potential of specific sites, the impact of erosion example, without access to capital, implementation of on both on-site and off-site resources, and preferences of technology that requires purchase of new farm implements the land user. or installation of elaborate terraces cannot occur. The conservation system must fit the scale of the land user. A On-Site and Off-Site Resources system requiring large equipment does not fit small fields on Landscapes and their associated soils are valuable on-site steep landscapes. resources used for many activities related to agriculture, The system must be culturally and socially acceptable. forestry, rangelands, wildlife, recreation, military training, Cultural acceptability concerns range from "What will mining, energy production, construction, transportation, neighbors think and say?" to implement having features waste disposal, reclamation of disturbed lands, and contrary to religious beliefs. Far more important than is conversion of land use. Protection against excessive erosion frequently recognized are the personal preferences of the and maintenance of both the landscape itself and high land user. Is the system convenient to farm and to manage? quality soil across the landscape is necessary for long-term Will the land user like the proposed system? If the land user sustainability for both the resource and the land user. is not pleased with a proposed conservation system, the Examples of off-site resources include air that receives likelihood of long-term use and maintenance of the system is dust from wind erosion and drinking water in a reservoir that dramatically reduced. receives sediment from both wind and water erosion. Sediment itself can be a pollutant and a carrier of other Indices of Resource Well-Being pollutants originating on farm fields where agricultural In general, conservation planning is choosing a system so chemicals are used and from waste disposal sites. that the detrimental impacts of erosion are within acceptable Sedimentation displaces volume in water conveyance limits as defined by indices that indicate the well being of structures like irrigation canals, stream channels, and resources impacted by erosion. Several indices are needed, *G.R. Foster, Agricultural Engineer (retired), USDA-Agricultural Research Service, National Sedimentation Laboratory, Oxford, Mississippi, USA. *Corresponding author: [email protected] because no single index addresses all erosional concerns for use of soil moisture by crops, loss of nutrients, change in associated with a resource. For example, maintenance of the soil texture by erosion, production of sediment that could ecological well being of rangelands is a high priority, and leave the site and cause off-site damage, and the likelihood soil resources are critically important for supporting plant that rilling and gullies would develop. These elements are, life. Protection of the soil against excessive erosion is for the most part, measurable. necessary to maintain productivity and a diverse plant Another element, just as important as these technical community. However, because rangeland ecology is related factors considered in setting T values, was the availability of to other factors besides soil, consideration must be given to conservation practices that farmers could use to meet T other processes besides erosion. That is, erosion control is values while maintaining profitability without undue not the sole interest in holistic conservation planning for any hardship. While the other factors are technical and scientific, land use. this factor considers feasibility that the conservation An index for well being of a resource must be technology can be implemented, government policy to understandable to those interested in the resource. The index encourage implementation of conservation, and economic must be measurable, and measurements must be repeatable and social considerations important to the land user. and consistent. The index should be based on scientific Other on-site impacts of soil erosion are important knowledge, including how the index represents the quality of besides removal of soil particles by erosion. Deposition the resource and how environmental processes and land use occurs within many fields, which can harm a growing crop, affect the index. and can change soil texture and other soil properties over the The conservation planning process therefore involves the long term. Wind driven sediment from wind erosion can use of an index related to maintenance of the soil and a damage plant seedlings, reduce yields and sometimes require mathematical model to estimate soil erosion rates. A set of replanting. acceptable conservation systems are proposed in relation to The scientific resources devoted to erosion prediction conditions of the specific site and preferences of the land technology far exceed those devoted to criteria for soil user. The mathematical soil erosion model is used to quality, including T values, and to understanding how estimate an erosion rate for each alternative, and this rate is erosion affects soil resources. Increased attention to compared to values for indices used to represent the well understanding how soil erosion affects the well being of soil being of on-site and off-site resources. The land user selects resources is greatly needed. from those practices having estimated soil erosion rates that are lower than those considered to be acceptable. Indices for Off-Site Impacts of Soil Erosion Thus, two technologies are important. One is the erosion Indices for the off-site impacts of soil erosion are not prediction technology and the second is the technology for nearly so well developed as soil loss tolerance T. Variables the indices used to describe resource well being. of great importance are the amount and rate of sediment reaching a given location and characteristics of that Indices for On-Site Impact of Soil Erosion sediment. The degree that these variables are important Erosion modifies soil properties by reducing soil depth, depends on the situation. Fine sediment in the water is not a changing soil texture, and removing nutrients and organic particular concern to navigation, but is a major concern matter. Erosion changes landscape properties by creating where the water is being used for drinking
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