The main soil properties affecting K are soil texture, including the amount of fine sand in addition to the usual sand, silt, and clay percentage used to describe soil texture, organic matter, structure, and permeability of the soil profile. In general terms, clay soils have a low K value because theses soils are resistant to detachment. Sandy soils have low K values because these soils have high infiltration rates and reduced runoff, and sediment eroded from these soils is not easily transported.
Silt loam soils have moderate to high K values because soil particles are moderate to easily detached, infiltration is moderate to low producing moderate to high runoff, and the sediment is moderate to easily transported. Silt soils have the highest K values because these soils readily crust producing high runoff rates and amounts.
Also, soil particles are easily detached from these soils, and the resulting sediment is easily transported. This mixture of effects illustrates that K is empirical. For example, using K to account for reduced soil loss from incorporation of manure is not proper and produces incorrect results. LS factor: The L and S factors jointly represent the effect of slope length, steepness, and shape on sediment production. RUSLE represents the combined effects of rill and interrill erosion.
Rill erosion is primarily caused by surface runoff and increases in a downslope direction because runoff increases in a downslope direction. Interrill erosion is caused primarily by raindrop impact and is uniform along a slope. Therefore, the L factor is greater for those conditions where rill erosion tends to be greater than interrill erosion.
Erosion increases with slope steepness, but in contrast to the L factor for the effects of slope length, RUSLE makes no differentiation between rill and interrill erosion in the S factor that computes the effect of slope steepness on soil loss.
Slope shape is a variation of slope steepness along the slope. Slope steepness and position along the slope interact to greatly affect erosion. Soil loss is greatest for convex slopes that are steep near the end of the slope length where runoff rate is greatest and least for concave slopes where the steep section is at upper end of the slope where runoff rate is least.
The LS factor is a measure of sediment production. Deposition can occur on concave slopes where transport capacity of the runoff is reduced as the slope flattens. This deposition and its effect on sediment yield from the slope is considered in the supporting practices P factor. C factor: The C factor for the effects of cover-management, along with the P factor, is one of the most important factors in RUSLE because it represents the effect of land use on erosion.
It is the single factor most easily changed and is the factor most often considered in developing a conservation plan. For example, the C factor describes the effects of differences between vegetation communities, tillage systems, and addition of mulches. The C factor is influenced by canopy cover above but not in contact with the soil surface , ground cover cover directly in contact with the soil surface , surface roughness, time since last mechanical disturbance, amount of live and dead roots in the soil, and organic material that has been incorporated into the soil.
These variable change through the year as plants grow and senesce, the soil is disturbed, material is added to the soil surface, and plant material is removed. The C factor is an average annual value for soil loss ratio, weighted according to the variation of rainfall erosivity over the year. The average annual distribution of erosivity during a year varies greatly with location. In the US, erosivity is nearly uniform throughout the year in the mid-south region, is concentrated in the late spring in the western cornbelt, and is concentrated in late fall and early winter in the Pacific coast region.
Soil loss ratio is the ratio of soil loss from a given land use to that from the unit plot at a given time. RUSLE computes soil loss ratio values as they change through time with each half month period using equations for subfactors related to canopy, ground cover, roughness of the soil surface, time since last mechanical disturbance, amount of live and dead roots in the upper soil layer, amount of organic material incorporated into the soil, and antecedent soil moisture in the Northwest Wheat and Range Region.
P factor: The supporting practice P factor describes the effects of practices such as contouring, strip cropping, concave slopes, terraces, sediment basins, grass hedges, silt fences, straw bales, and subsurface drainage. These practices are applied to support the basic cultural practices used to control erosion, such as vegetation, management system, and mulch additions that are represented by the C factor.
Supporting practices typically affect erosion by redirecting runoff around the slope so that it has less erosivity or slowing down the runoff to cause deposition such as concave slopes or barriers like vegetative strips and terraces. The major factors considered in estimating a P factor value include runoff rate as a function of location, soil, and management practice; erosivity and transport capacity of the runoff as affected by slope steepness and hydraulic roughness of the surface; and sediment size and density.
Version 1. It, along with data files, can be downloaded from this web site. RUSLE was first released for widespread use in late as version 1.
That agreement expired in Should you need a copy of version 1. New features in version 1. NRCS continued its implementation-using version 1. Another interim version, 1. This UNIX-based model has been implemented in field offices in several states.
The differences between this version and 1. RUSLE2 will be very flexible and customizable to particular user preferences. It will also allow a choice of units between the U. Expected release date is Appendix 8. Appendix 9. Appendix Origination and Underwriting Overview. Property and Appraisal Requirements.
Submitting the Application Package. Closing the Loan and Requesting the Guarantee. Regular Servicing-Performing Loans. Loss Claim - Collecting on the Guarantee. Unnumbered Letter and State Supplements. Processing Final Applications - Stage 2. Participating with Other Funding Sources. Loan Closing and Project Lease-Up. Subsequent Loans and Loans for Final Payments. Farm Labor Housing Loans and Grants.
Forms Referenced in the Handbook. Cover Page. USDA is working to build a fairer, more competitive, and more resilient meat and poultry supply chain. Our thoughts are with local communities and our employees who are facing unprecedented devastation. Farmers and Ranchers, this is your opportunity to help shape the future of agriculture by being counted.
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