United States Department of Agriculture 393-CPS-1

NRCS, NHCP

February 2024

Notice of Proposed Changes to the National Handbook of Conservation Practices 

for the Natural Resources Conservation Service

[Docket No. NRCS-2023-0022]

PROPOSED FULL TEXT FOR PRACTICE STANDARD CODE 393

NRCS reviews and periodically updates conservation practice standards. To obtain the current 

version of this standard, contact your Natural Resources Conservation Service State office or 

visit the Field Office Technical Guide online by going to the NRCS website at 

https://www.nrcs.usda.gov/ and type FOTG in the search field. 

USDA is an equal opportunity provider, employer, and lender.

Natural Resources Conservation Service 

CONSERVATION PRACTICE STANDARD 

FILTER STRIP 

CODE 393 

(ac)

DEFINITION 

A strip or area of herbaceous vegetation, located at the lower edge(s) of afield, that removes contaminants

from overland flow. 

PURPOSE 

This practice is used to accomplish one or more of the following purposes– 

• Reduce suspended solids and associated contaminants in runoff and excessive sediment in

surface waters. 

• Reduce dissolved contaminant loadings in runoff to surface waters. 

• Reduce suspended solids and associated contaminants in irrigation tailwater and excessive

sediment in surface waters. 

CONDITIONS WHERE PRACTICE APPLIES 

Filter strips are established where environmentally sensitive areas need to be protected from sediment,

other suspended solids, and dissolved contaminants in runoff. 

CRITERIA 

General Criteria Applicable to All Purposes 

The filter strip will be located immediately downslope from the source area of contaminants. 

Overland flow entering the filter strip will be uniform sheet flow. 

Concentrated flow will be dispersed before it enters the filter strip. 

The maximum gradient along the leading edge of filter strip will not exceed one-half of the up-and-downhill slope percent, immediately upslope from the filter strip, up to a maximum of five percent. 

Filter strips will not be used as a travel lane for equipment or livestock. 

Vegetation 

Plant species, rates of seeding (lbs/ac), vegetative planting (plants/ac), minimum quality of planting stock

(pure live seed [PLS] or stem caliper), and method of establishment shall be specified before application.

Only viable, high quality seed or planting stock will be used. 

Perform site preparation and seeding/planting at a time and in a manner that best ensures survival and

growth of selected species. Successful establishment parameters, (e.g., minimum percent ground/canopy

cover, percent survival, stand density) will be specified before application. 
 Additional Criteria to Reduce Dissolved Contaminants, Suspended Solids and Associated Contaminants in Runoff and Excessive Sediment in Surface Waters 

The filter strip will be designed to have a 10-year life span, following the procedure in Agronomy Technical

Note No. 2, “Using Revised Universal Soil Loss Equation, Version 2 (RUSLE2) for the Design and

Predicted Effectiveness of Vegetative Filter Strips (VFS) for Sediment.,” This is based on the amount of

sediment delivery to the upper edge of the filter strip and ratio of filter strip flow length to length of flow

path from the contributing area. The flow length through the filter strip will be based on Agronomy

Technical Note No. 2 with a minimum length of 20 feet for suspended solids and associated contaminants

in runoff and 30 feet for dissolved contaminants and pathogens in runoff. 

The drainage area immediately above the filter strip will have a slope of one percent or greater. 

 Vegetation 

The filter strip will be established to permanent herbaceous vegetation. 

Species selected will be— 

• Able to withstand partial burial from sediment deposition. 

• Tolerant of herbicides used on the area that contributes runoff to the filter strip. 

• Stiff stemmed and a high stem density near the ground surface. 

• Suited to current site conditions and intended uses. 

• Able to achieve adequate density and vigor within an appropriate period to stabilize the site

sufficiently to permit suited uses with ordinary management activities. 

Schedule planting during periods when soil moisture is adequate for germination and establishment.

Seeding will be timed so that tillage for adjacent crop does not damage the seeded filter strip. 

 Do not burn the filter strip more than once every 10 years. 

Where the purpose is to remove phosphorus, remove (or harvest) the filter strip aboveground biomass at

least once each year. 

The minimum seeding and stem density will be equivalent to the seeding rate for a high quality grass hay

seeding rate for the climate area or the density of vegetation selected in current water erosion technology

to determine trapping efficiency, whichever is the higher seeding rate. 

 Additional Criteria to Reduce Suspended Solids and Associated Contaminants in Irrigation Tailwater and Excessive Sediment in Surface Waters 

Filter strip vegetation will be a small grain or other suitable annual plant. 

The seeding rate shall be sufficient to ensure that the plant stem spacing does not exceed one inch (about

144 plant stems per square foot). 

Establish the filter strip prior to the irrigation season so that the vegetation is mature enough to filter

sediment from the first irrigation. 

CONSIDERATIONS 

General Considerations 

Filter strip width (flow length) can be increased as necessary to accommodate harvest and maintenance

equipment. 

A filter strip with the leading edge on the contour will function better than those with a gradient along the

leading edge. 

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 Seeding rates that establish a higher stem density than the normal density for a high quality grass hay

crop will be more effective in trapping and treating contaminants. 

 When needed, control invasive plant species. 

Consideration for Reducing Suspended Solids and Associated Contaminants in Runoff 

Increasing the width of the filter strip beyond the minimum required will increase the potential for capturing

more contaminants in runoff. 

While this practice reduces pathogen movement in the agricultural landscape, it should not be assumed

that it will reliably reduce pathogens in receiving water to levels consistent with food safety standards for

produce crops. See the U.S. Food & Drug Administration Food Safety Modernization Act Final Rule on

Produce Safety at http://www.fda.gov/food/guidanceregulation/fsma/ucm334114.htm. 

Considerations for Creating, Restoring or Enhancing Herbaceous Habitat for Wildlife and Beneficial Insects and Pollinators 

Filter strips are often the only break in the monotony of intensively cropped areas. The wildlife and

pollinator benefits of this herbaceous cover can be enhanced by the following: 

• When appropriate, use native grass species that fulfill the purpose(s) of the practice while also

providing habitat for priority wildlife. 

• Add herbaceous plant species (including native forbs) to the seeding mix that are beneficial to

wildlife and pollinators and are compatible for one of the listed purposes. Changing the seeding mix

should not detract from the purpose for which the filter strip is established. 

• Increase the width beyond the minimum required. The additional area can increase food and cover

for wildlife and pollinators. 

• Management activities on filter strips (mowing, burning, or light disking), should not be done more

often than every other year with frequency dependent on geographical location to maintain the

purpose(s) of the practice. 

• Management activities should be completed outside of the primary nesting, fawning, and calving

seasons. Activities should be timed to allow for regrowth before the growing season ends. 

• Organic producers should submit plans and specifications to their certifying agent for approval prior

to installation, as part of the organic producer’s organic system plan. 

Considerations to Maintain or Enhance Watershed Functions and Values 

Filter strips may be used to enhance connectivity of corridors and non-cultivated patches of vegetation

within the watershed, enhance the aesthetics of a watershed, and be strategically located to reduce runoff,

and increase infiltration and groundwater recharge throughout the watershed. 

Considerations to Increase Carbon Storage 

Increasing the width of the filter strip beyond the minimum required will increase potential for carbon

sequestration. 

PLANS AND SPECIFICATIONS 

 Develop plans and specifications for each field or treatment unit according to the Criteria section

requirements above, and operation and maintenance section requirements below. Specifications must

describe the requirements to apply this practice to achieve the intended purpose. Record the following

specification components in an approved Filter Strip (Code 393) implementation requirements document. 

• Practice purpose(s). 

• Length, width (width refers to flow length through the filter strip), and slope of the filter strip to

accomplish the planned purpose(s). 

• Plant species selection and seeding/planting/sprigging rates to accomplish the planned purpose. 

• Planting dates and planting method(s). 

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• Specific care and handling requirements of the seed or plant material to ensure that planted

materials have an acceptable rate of survival. 

• A statement that only viable, high quality, and adapted seed will be used. 

• Site preparation instructions sufficient to establish and grow selected species. 

OPERATION AND MAINTENANCE 

For the purposes of filtering contaminants and nutrients (phosphorus), permanent filter strip vegetative

plantings will be harvested and removed as appropriate to encourage dense growth, maintain an upright

growth habit and remove nutrients and other contaminants that are contained in the plant tissue. 

Control undesired weed species, especially State-listed noxious weeds. 

If Conservation Practice Standard (CPS) Prescribed Burning (Code 338) is used to manage and maintain

the filter strip, an approved burn plan must be developed and consistent with Additional Criteria to Reduce

Dissolved Contaminants, Suspended Solids and Associated Contaminants in Runoff and Excessive

Sediment in Surface Waters, do not burn the filter strip more than once every ten years. 

Inspect the filter strip after storm events and repair any gullies that have formed, remove unevenly

deposited sediment accumulation that will disrupt sheet flow, reseed disturbed areas and take other

measures to prevent concentrated flow through the filter strip. 

Apply supplemental nutrients as needed to maintain the desired species composition and stand density. 

Periodically regrade and reestablish the filter strip area when sediment deposition at the filter strip-field

interface jeopardizes its function. Reestablish the filter strip vegetation in regraded areas, if needed. 

If grazing is used to harvest vegetation from the filter strip, the grazing plan must ensure that the integrity

and function of the filter strip is not adversely affected. 

REFERENCES 

Dillaha, T.A., J.H. Sherrard, and D. Lee. 1986. Long-Term Effectiveness and Maintenance of Vegetative

Filter Strips. VPI-VWRRC Bulletin 153. 

Dillaha, T.A., and J.C. Hayes. 1991. A Procedure for the Design of Vegetative Filter Strips: Final Report

Prepared for U.S. Soil Conservation Service. 

Dosskey, M.G., M.J. Helmers, and D.E. Eisenhauer. 2008. A Design Aid for Determining Width of Filter

Strips. Journal of Soil and Water Conservation. July/Aug 2008—vol. 63, no. 4. 

Foster, G.R. 2005. Revised Universal Soil Loss Equation, Version 2 (RUSLE2) Science Documentation (In

Draft). USDA-ARS, Washington, DC. 

Muñoz-Carpena, R., Parsons, J.E.,2011. VFSMOD-W Vegetative Filter Strips Modelling System. Model

Documentation and User’s Manual, University of Florida 6.x. 

Renard, K.G., G.R. Foster, G.A. Weesies, D.K. McCool, and D.C. Yoder, coordinators. 1997. Predicting

Soil Erosion by Water: A Guide to Conservation Planning with the Revised Universal Soil Loss Equation

(RUSLE). U.S. Department of Agriculture. Agriculture Handbook 703. 

Revised Universal Soil Loss Equation Version 2 (RUSLE2) Web site (checked October 2020):

http://fargo.nserl.purdue.edu/rusle2_dataweb/RUSLE2_Index.htm.

U.S. Food & Drug Administration Food Safety Modernization Act Final Rule on Produce Safety (checked

October 2020): http://www.fda.gov/food/guidanceregulation/fsma/ucm334114.htm

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NRCS, NHCP

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February 2024