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 For a grass filter strip Doyle et al. (1977) found phosphorus reduction at 62%. Willrich and
Boda found 62% of phosphorus removal with loading rates 5-15 cm/week and 46% phosphorus
removal at loading rates of 20-25 cm/week. Other studies report higher filter strip treatment
effectiveness in the range of 75-80 for sediment and nutrient concentrations (Yang et al. 1980; Dickey
and Vanderholm 1981; Edwards et al. 1983; Dillaha 1986). Still others Overcash et a. (1976) and
Young et al. (1978) report effectiveness for reducing total phosphorus at 87 and 88%. For studies
using forest buffers and orchard grass, corn stubble and tilled plots, Dolye et al. (1977) and Thompson
et al. (1979) found soluble and total phosphorus levels were reduced to background levels.
For treating milkhouse waste, Barker and Young (1985) showed a settling basin in line before a
filter strip removed total phosphorus up to 68-98% by concentration and 98% by mass. Total nitrogen
effectiveness was up to 45-98% by concentration and 99% by mass. Schwer and Clausen (1989) also
treated milkhouse waste with a vegetative filter. Phosphorus removal on concentration basis was 86%
and 89% by mass. Total nitrogen removal was 83% on a concentration basis and 92% by mass. For
both milkhouse waste filter studies authors stress the importance of keeping within the hydraulic loading
capacity of the filter.
Nutrient Management Systems . Nutrient management systems address requirements for
soil fertility and protection of water quality. Nutrient sources include organic wastes, chemical fertilizer,
soil reserves, and crop residues. Nutrient management systems reduce the availability and movement of
nutrients by controlling the amount, source, form, placement, and timing of application to crop and
forage areas.
The rate of nitrogen application should match the needs on the crop based on realistic yield
goals. Losses of both nitrogen and phosphorus increase with increasing application beyond what is used
by the plant (NWQEP 1982b; Baker and Johnson 1983, WDATCP 1989). For the application of
both manure and chemical fertilizers, soil testing is an essential BMP to assess crop nitrogen and
phosphorus needs. Credit for nitrogen input by legumes and manure should be considered in the
nitrogen recommendation. Proper rates can reduce nitrogen losses by 35-94% as compared to
excessive rates (NWQEP 1982b) . Excessive rates of application increase the potential for nitrate
leaching into ground water supplies.
Losses of nutrients are also highly influenced by the timing of application in relation to runoff
events. As the time between nutrient application and runoff increases, especially if there is crop uptake,
the chances of losses are decreased significantly. The timing of application should be just prior to or
during the maximum nutrient uptake, as either spring or summer. Split nitrogen application can reduce
potential losses by up to 30% as compared to a single application (NWQEP 1982b) .
The National Water Quality Evaluation Project (1982a) found when applying manure in the fall,
up to 50% of the total nitrogen can be lost through decomposition and leaching. Winter manure
4.2-15
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