Filter Strips (NRCS #393)

Applicable Systems

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About

Filter strips¹ are vegetated areas generally located along the lower edge(s) of fields to protect sensitive areas. They serve as a natural filter that intercept sediments, nutrients, and other constituents from agricultural fields thus protecting water bodies, wetlands and other susceptible area. Many of the benefits associated with filter strips are due to increases in infiltration². Long-term effectiveness depends on the type of vegetation³, and performance often improves in the years following establishment².

Key aspects and considerations:

Design filter strips for a 10-year life span.
Introduce permanent herbaceous vegetation.
Select species with high density cover, herbicide tolerant, and ability to withstand partial burial from sediment deposit.
Consider slopes between 5 and 15% for best effectiveness.
Plant wider strips for the greatest runoff and sediment reduction⁴.
Avoid establishing in areas with a shallow water table, as filter strips will likely be less effective.

Benefits and Limitations

ACRE Category	Benefits	Limitations
Soil Health	Traps sediment from runoff. Reduces soil erosion and improves aggregate formation. Increases soil organic matter due to permanent cover and lack of soil disturbance. Increases absorption of contaminants by plant roots and breakdown with biological activity.	Sediment accumulation may require periodic maintenance.
Water Management	Enhances water infiltration, groundwater recharge, and plant water availability. Improves surface and groundwater quality by slowing runoff and reducing transportation of sediments, nutrients, pathogens and other contaminants. Reduces risk of flooding.	Less effective during intense rainfall events with concentrated flow.
Nutrient Management	Improves nutrients availability for plants by trapping nutrients in the field. Increases cation exchange capacity and nutrient hold by increasing organic matter. Decreases fertilizer losses from adjacent fields.	N/A
Agricultural Production	Preserves long-term soil productivity by protecting adjacent field from gully formation and edge erosion. Enhances pest and weed suppression.	Pathogens mortality may be delayed because vegetative cover protects them from desiccation.
Biodiversity and Wildlife	Increases diversity of soil organisms. Provides habitat and food for insects and wildlife. Enhances aquatic habitat for fish and other aquatic organisms. Promotes wildlife corridors across agricultural landscapes.	May harbor weeds or wildlife species that require specific management.
GHG Emission	Perennial grasses and deep-rooted plants have potential to offset CO₂ emissions and store C in plants biomass and soil; Supports long-term carbon storage.	In wet and saturated soils, denitrification of N-rich fertilizer received from the fields can increase N₂O emissions.
Economics	Programs for cost-share and incentive payments can offset establishment costs and make filter strips more viable for farmers. Farmers can make extra revenue by harvesting for hay or biomass, and by providing grazing. Economic gains are indirect and associated with long-term benefits.	Opportunity cost from land taken out of production, that can have big economic impact in highly productive fields⁴. There are costs associated with site preparation, seeding, and periodic maintenance. Filter strips require inspection after storm events and removal of unevenly deposited sediment accumulation. Annualized field strip costs were estimated to range from $314 to $865 ha^-1 year^-1 for different implementations⁴.

Impact on Agricultural Resilience

Buffers extreme rainfall and flooding by slowing down runoff and increasing infiltration, making water available for plants in dry periods.
Reduces soil degradation under drought and heavy rain by improving soil structure.
Intercepts contaminates (sediment, nutrients, pesticides, pathogens) in field runoff thus protecting soil and water quality.

Regional Applicability

The NRCS and the Minnesota Department of Agriculture make some recommendations for Filter Strips and Field Border practices to protect soil from erosion and reduce sediments and contaminants into runoff.
Kansas State Research and Extension shows how vegetative filter strip systems can be applied for controlling and reducing nutrient runoff from confined animal feeding operations into surface water.
Prairie strips, which are field strips with prairie vegetation, associated with corn and soybean fields in central Iowa, reduced water runoff, increased soil and nutrient retention, as well as birds and pollinators abundance⁵.

Case Studies

Across central Iowa, there are many successful case studies implementing prairie strips⁵, a version of filter strips with prairie vegetation. Planting 10% of fields to prairie strips can reduce sediment and nutrient loss. "The whole key to farming in Iowa is to be able to consistently do the same practice over 2,000 acres in the couple of days mother nature gives you the field conditions you need. Managing that risk is huge and prairie strips is something one could control. You do it, it's there, and you don't have that ongoing seasonal risk as you do with cover crops", states Mollie Aronowitz from The Luze Farm.

Resources

Video. Iowa NRCS: Conservation Choices Practice Spotlight: Filter Strips
Video. Sand County Foundation: Prairie Strips webinar#1: A new conservation practice for farmers and crop consultants
Iowa State University: Science-Based Trials of Rowcrops Integrated with Prairie Strips
Michigan Conservation Reserve Enhancement Program (CREP). CP 21 - Filter Strips
Sand County Foundation: Estimating the Water Quality Benefits of Prairie Strips Using SnapPlus
University of Florida Extension: Vegetative Filter Strips -- A Best Management Practice for Controlling Nonpoint Source Pollution
USDA National Resources Conservation Service (NRCS) - Using RUSLE2 for the Design and Predicted Effectiveness of Vegetative Filter Strips (VFS) for Sediment

References

USDA-NRCS (2016). Conservation Practice Standard Document, Filter Strip, Code 393. https://www.nrcs.usda.gov/sites/default/files/2022-09/Filter_Strip_393_CPS.pdf
Dosskey, M. G., Hoagland, K. D., & Brandle, J. R. (2007). Change in filter strip performance over ten years. Journal of Soil and Water Conservation, 62(1), 21-32. https://doi.org/10.1080/00224561.2007.12435916
Lee, K-H., Isenhart, T. M., Schultz, R. C. & Mickelson, S. K. (1998). Nutrient and sediment removal by switchgrass and cool-season grass filter strips in Central Iowa, USA. Agroforestry Systems, 44, 121--132. https://doi.org/10.1023/A:1006201302242
Douglas-Mankin, K. R., Helmers, M.J., & Harmel, R.D. (2021). Review of Filter Strip Performance and Function for Improving Water Quality from Agricultural Lands. Transactions of the ASABE, 64(2), 659-674. https://doi.org/10.13031/trans.14169
Schulte, L. A., Niemi, J., Helmers, M. J., Liebman, M., Arbuckle, J. G., James, D. E., ... & Witte, C. (2017). Prairie strips improve biodiversity and the delivery of multiple ecosystem services from corn--soybean croplands. Proceedings of the National Academy of Sciences, 114(42), 11247-11252. https://doi.org/10.1073/pnas.1620229114
NPDES: Stormwater Best Management Practice -- Vegetated Filter Strip. https://www.epa.gov/system/files/documents/2021-11/bmp-vegetated-filter-strip.pdf
USDA-NRCS (2016). Conservation Practice Standard Overview, Filter Strip (Code 393). https://www.nrcs.usda.gov/sites/default/files/2022-09/Filter_Strip_393_Overview_Sep_2016.pdf

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Filter Strips photo 1 — Photo 1: Filter strip along a field in Dubuque County, Iowa.

Courtesy of Iowa NRCS photo by Jason Johnson.

Filter Strips photo 2 — Photo 2: When planted with appropriate species, filter strips can provide pollinator and wildlife habitat.

Courtesy of Iowa NRCS photo by Jason Johnson.

Filter Strips photo 3 — Photo 3: A filter strip along the two sides of a creek in an Iowa field.

Courtesy of Iowa NRCS photo by Jason Johnson.