Review of filter strip performance and function for improving water quality from agricultural lands

Authors: Mankin, Kyle; HELMERS, MATTHEW - Iowa State University; Harmel, Daren

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2020
Publication Date: 4/16/2021
Citation: 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.
DOI: https://doi.org/10.13031/trans.14169

Interpretive Summary: Filter strips (FSs) are common agricultural conservation practices to improve water quality from agricultural fields. This study summarizes, analyzes, and interprets data from 74 previous studies to assess how effective FSs have been in reducing sediment, nutrients, pesticides, and pathogens. This study also fills an important gap by assessing FS cost effectiveness. Results showed that larger FS widths, up to about 15 m, captured more runoff. Sediment reduction improved as FS area (relative to the upslope drainage area) increased and as FS width increased, up to about 20 m. Total P and total N reduction decreased for FS soils with greater ability to conduct water, and total N reduction also improved as FS width increased. Both total P and total N reduction tended to increase with increasing FS width up to about 20 m and with increasing FS slope up to about 10%. Annualized FS costs were estimated to be about $314-865 per hectare per year or $10.3-18.6 per thousand kilograms of sediment removed. Much of the cost is the opportunity cost of taking FS land out of production. FS monitoring recommendations are discussed, acknowledging the challenges with implementing real-world FS studies. This information will be useful to guide on-farm and agency program decisions related to FSs and to increase the scientific understanding of this commonly used agricultural conservation practice.

Technical Abstract: Filter strips (FSs) are common edge-of-field conservation practices implemented to reduce flux of sediment, nutrients, and other constituents from agricultural fields. While various aspects of FS effectiveness have been reviewed, the present study provides a comprehensive summary of FS efficiency data for sediment, nutrients, pesticides, and pathogens as part of a Special Collection focused on agricultural conservation practices. The present analysis also fills an important gap assessing performance-based FS costs and cost-effectiveness. Data from 74 U.S. and international studies with 294 different treatments and 3,050 replications were compiled and analyzed. Results showed that runoff reduction tended to increase with increasing FS width up to about 15 m and that sediment reduction was significantly related to FS area to drainage area ratio and FS width, with reduction tending to increase with increasing width up to about 20 m. Total P reduction was significantly related to FS soil saturated hydraulic conductivity, and total N reduction was significantly related to both saturated hydraulic conductivity and width. Both total P and total N reduction tended to increase with increasing FS width up to about 20 m and with increasing FS slope up to about 10%. Annualized FS costs were estimated to range from $314-865/ha/yr for different FS implementations. A major component of the cost is the opportunity cost of land out of production. Costs per unit of sediment retained by FS systems ranged from $10.3-18.6/Mg. A comprehensive assessment of FS cost-effectiveness (cost:benefit) is needed. Monitoring recommendations are discussed, acknowledging the challenges with implementing field-scale FS studies. This information is a critical to guide on-farm and programmatic FS decisions and to increase the scientific understanding of this commonly used agricultural conservation practice.