The following is the final section of a three part series on Vegetative Filter Strips (VFS) and their role and use in reducing the potential for nutrient transport from crop and pasture fields due to overland flow. Information was excerpted from "Grassed Filter Strips Can Reduce Losses of Nitrogen and Phosphorus in Runoff", by D. R. Edwards, P. A. Moore, Jr., and T. C. Daniel. The original article appeared in the Better Crops with Plant Food Journal, Volume 80, (1996, No. 4), pages 8 to11).
Installation and maintenance of VFS are critical to ensure that they perform as expected. Simply speaking, VFS can be very effective at reducing the potential for nutrient and sediment runoff from fertilized fields, either where inorganic fertilizers or livestock manure has been spread on the surface. However, in order for VFS to be effective, some general guidelines and processes should be understood and followed:
§ VFS should be installed on the contour, without regard to fence or property lines. The filters should be laid out upstream of any defined channels, i.e., the runoff should be filtered before it reaches the point that even small channels begin to develop or form.
§ Similarly, the filters should be maintained so that "sheet flow" occurs across the filter, as opposed to concentrated flow in even small channels.
§ VFS are not likely to be very effective in fields with irregular topography and having many low regions that function as small channels during runoff.
§ Unless the VFS are properly installed, it is questionable whether they provide any measurable benefit.
§ VFS, just like the up slope areas, should be fertilized; the amount of nutrients entering the VFS is quite small in agronomic terms. Additional fertilizer should be added as necessary to ensure a good stand of grass within the filter. Perhaps the best time to fertilizer the VFS is some time after the first runoff has occurred from the fertilized field.
Summarizing the results of Edwards et al., regardless of the source (organic or inorganic) runoff losses of N and P from fertilized pasture or where manure has been spread are relatively small proportions of the amount applied. These losses are also associated primarily with soluble N and P forms rather than particulate forms. Consequently, simply reducing erosion from pasture fields will have little impact on reducing nutrient losses. Grassed filter strips can be quite effective in reducing nutrient losses. However, the key to using VFS to the best advantage is to use the appropriate length and install and maintain them properly.
Categories: Filter Strips, Water Quality
Date: 1997