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Yield Grass Seed Production and Water Quality Protection HandbookHigh
Yield Grass Seed Production and Water Quality Protection Handbook| Nutrient Management | Residue
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Maintenance of high-quality water in groundwater and streams is essential for maintaining human and wildlife health in the Pacific Northwest. The "Oregon Plan" for salmon recovery places emphasis on watershed restoration, which includes reducing urban, industrial and agricultural impacts on the quality of streams. With a large portion of the western Oregon landscape in grass seed crops, growers must be mindful of their potential impact on water quality.
In the south Willamette Valley counties of Linn, Benton and Lane, for example, there are approximately 400,000 acres of cropland. Of that, about 277,000 acres, or 77 percent, is devoted to seed production. Grass seed is the major crop along or near most streams on the valley floor.
The concentrations of nitrate, ammonium, nitrite, soluble phosphorus and diuron from shallow wells and surface waters moving through established grass seed production fields have been shown to be below water quality standards or recommendations established by the U.S. Environmental Protection Agency. Averaged over the season, nitrogen (N) concentrations in poorly drained riparian zones are low and mostly undetectable. Levels in grass fields averaged less than 4 ppm nitrate-N. Again, this is low relative to the drinking water standard of 10 ppm nitrate-N, and less than that typically found in most traditional summer annual cropping systems. Plant and soil bacterial processes are responsible for much of the nutrient retention that help minimize nitrate leaching and runoff. The N in the grass seed crop itself accounts for much of the soil N available to the crop.
Riparian areas next to cropland are effective in reducing shallow groundwater nitrate to low levels during months of low precipitation but during high precipitation periods, much of the perched water bypasses the riparian sub-soil zones and less N is processed through soil and plant processes. This points out the importance of good land and crop management practices, such as those used on many grass seed fields in western Oregon.
Grass seed crops have the greatest potential to impact water quality during the establishment year. The potential impact on water quality during the establishment year can be higher because of crop management practices such as plowing, disking and harrowing. These farm practices increase organic matter and N mineralization and thus facilitate the release of soil C and nitrate from the soil. This can contribute to greater soil erosion and nitrate loss to waterways.
Grass seed farmers in the Willamette Valley have long recognized that erosion on new plantings and fallow ground can be a problem, especially when unusually heavy rainfall occurs in the winter months, as it did in 1964 and again during the 1996 floods. The Soil and Water Conservation District (SWCD) for decades has focused on conservation efforts to reduce erosion and can provide valuable information to growers that will help protect soil. For example, improving field drainage through ditching, deepening drainage ways and installing drain tiles have been key conservation practices promoted by the SWCD and Soil Conservation Service to reduce surface runoff, in addition to improving crop production. These practices are still effective in this regard. Although drainage of "wetlands" is no longer recommended or permitted, improving drainage on most grass seed fields ("prior converted" cropland) is allowed.
Improving field drainage is only part of the solution. No-till or conservation tillage combined with leaving full-straw loads in fields can substantially reduce erosion, as well as improve soil quality. In the long run, these management tools may also help to improve economic yield. USDA-ARS is actively addressing these issues with current cropping systems research.