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Sediment removal.
Intensive management of conservation buffers is required to maintain
pesticide-trapping efficiency. Sediment trapped by buffers changes
land shape and may cause runoff to flow parallel to buffers rather
than across them. Similarly, sediment trapped in the center of grassed
waterways may cause runoff to flow along the edge of waterways,
eroding gullies and increasing concentrated flow. Sediment will
have to be removed periodically from these areas and vegetation
reestablished when necessary. It is critical that sediment loads
flowing across buffers be limited as much as possible by soil conservation
practices applied to source fields. The draft NRCS Conservation
Practice Standard for Filter Strips requires that average sheet
and rill erosion above the filter strip shall be less than 10 tons
per acre per year.
Mowing. Buffers may require mowing for
weed control or aesthetic reasons. Mowing can both positively and
negatively affect pesticide trapping efficiency. Mowing can encourage
some grass species to tiller and produce denser vegetation at the
soil surface. Mowing too short, especially with stiff-stemmed species,
may reduce the flow retardence of the vegetation. Actively growing
vegetation will be more biologically active, absorbing and degrading
pesticides, and supplying carbon for microbial degradation.
Harvest of grass
or trees.
One of the functions of conservation buffers is to trap nutrients
such as nitrogen and phosphorus. Periodic harvest of buffer vegetation
removes trapped nutrients from the system, preventing eventual release
to the soil and potential movement to water.
Impact of trapped
herbicides. Herbicides trapped by buffers are degraded in the soil by
microbial and chemical processes. Some herbicide may be taken up
by buffer plants either by roots or through foliage and metabolized.
However, it is possible that excessive loads of certain herbicides
could injure buffer plants. Some preemergence herbicides have little
impact on established plants. However a few, such as the triazines,
can injure grasses if present in high enough concentrations. Most
buffer studies have reported either no injury to buffer grasses
or only slight injury. In Iowa, bromegrass in buffers grew more
vigorously nearest source areas, apparently due to nutrients trapped
by the buffer (Arora et al., 1996). Atrazine, cyanazine, and metolachlor
trapped by the buffers did not harm the grass. Grass seedlings are
most sensitive to herbicides in runoff. Thus, the greatest chance
for harmful impact of herbicides in runoff would appear to occur
in the seeding year. Warm season grasses such as switchgrass, big
bluestem, and bermudagrass are tolerant to triazine herbicides and
would not be injured by runoff.
Avoid overspray. While herbicide concentrations
in runoff are usually tolerated by buffers, direct application or
drift of some herbicides can be harmful to grasses or woody plants.
Nonselective herbicides used as burndown treatments in no-till production
systems and on some herbicide tolerant crop varieties can be especially
damaging to buffer vegetation. Care should be taken to turn off
spray booms and use control drip nozzles when driving over buffers,
or when booms extend over buffers when turning. Squaring up cropland
areas by varying buffer widths along irregular streams or field
borders makes application of herbicides easier, with fewer "point
rows" and chances for overspray over buffers.
Turning on buffers.
While buffers at the edge of fields make convenient turning areas,
driving heavy equipment on buffers can cause damage, compacting
soil and reducing water infiltration, and causing ruts when soil
is wet. Ruts may then encourage concentrated flow which bypasses
filtering ability of the buffer. Driving on buffers should be avoided
as much as possible, especially under wet soil conditions.
Livestock grazing. Grazing reduces buffer efficiency by causing
compaction and reducing grass heights. Woody species may also be
injured. Livestock may also cause significant stream bank degradation
and directly contaminate water. Some livestock producers would like
to allow livestock access to fields adjacent to buffers for limited
times without having to fence buffers, such as to allow gleaning
of waste grain following harvest. Planning a grazing system that
allows quick, intensive foraging under good soil moisture conditions
is essential. Removing livestock when soils are wet reduces potential
damage to buffers.
Weed control. Buffers may harbor weeds requiring
control. Vigorous grass growth prevents growth of many annual weeds,
but some perennial weeds may require either mowing or spot treatment
with herbicides. Noxious weeds must be controlled in the buffer.
Insect concerns. Buffers may harbor insect pests
which move into crop fields. In some cases, such grassy areas are
sprayed with insecticides to prevent damage to adjacent crops. If
necessary, such treatments should be selected considering potential
risks to adjacent aquatic ecosystems. Buffers also can be a safe
harbor for beneficial insects. Populations of these insects can
build up within the buffer areas and stay outside the cropland area
treated with insecticides. Vegetation and buffer maintenance are
tailored to promoting beneficial insect populations within buffer
areas.
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