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NATURAL RESOURCES CONSERVATION SERVICE
CONSERVATION PRACTICE STANDARD
CONTOUR BUFFER STRIPS
(Ac.)
CODE 332
DEFINITION
Narrow strips of permanent, herbaceous
vegetative cover established around the hill
slope, and alternated down the slope with
wider cropped strips that are farmed on the
contour.
PURPOSE
This practice is applied to support one or more
of the following purposes:
• Reduce sheet and rill erosion.
• Reduce water quality degradation from the
transport of sediment and other water-
borne contaminants downslope.
• Improve soil moisture management
through increased water infiltration.
• Reduce water quality degradation from the
transport of nutrients downslope.
CONDITIONS WHERE PRACTICE APPLIES
This practice applies on all sloping cropland,
including orchards, vineyards and nut crops.
Where the width of the buffer strips will be
equal to or exceed the width of the adjoining
crop strips, the practice Stripcropping (code
585) applies.
CRITERIA
General Criteria Applicable to All Purposes
Surface flow from contoured crop rows must
be delivered to a stable outlet.
Design the width of the cropped strip to
accommodate some multiple of full equipment
width.
Do not plant buffer strips with any plants listed
on the noxious weed list of the state.
Do not use buffer strips as travel lanes for
livestock or equipment.
Buffer strips are not a part of the normal crop
rotation (however, they may be harvested or
grazed), and will remain in place until they
need to be renovated or re-established.
Row Grade. When the row grade of any crop
strip reaches the maximum allowable design
grade, establish a new baseline up or down
slope from the last buffer strip for the layout of
the next crop strip.
Arrangement of Strips. A crop strip will
occupy the area at the top of the hill, unless
unusually complex topography requires
vegetation in this area in order to establish a
farmable system.
When used in combination with terraces,
diversions or water and sediment control
basins, the layout of the buffer strips shall be
coordinated with the grade and spacing of the
other practices so that the buffer strip
boundaries will parallel the practices as closely
as possible. Locate the buffer strip
immediately upslope from the terrace channel,
or diversion, or the storage area of the water
and sediment control basin.
Additional Criteria to Reduce Sheet and Rill
Erosion
Minimum Row Grade. The cropped strips
will have sufficient row grade to ensure that
runoff water does not pond and cause
unacceptable crop damage.
Maximum Row Grade. The maximum row
grade will not exceed:
• One-half of the up-and-down hill slope
percent used for conservation planning, UORU
2%, whichever is less.
NRCS, NHCP
September 2014
Conservation practice standards are reviewed periodically and updated if needed. To obtain
the current version of this standard, contact your Natural Resources Conservation Service
State Office or visit the Field Office Technical Guide.
332 - 2
• Up to 3% row grade is allowed for a
maximum of 150 feet as crop rows approach a
stable outlet.
Width of Strips. The minimum width will be
• At least 15 feet wide for strips planted to
grasses or grass-legume/forbs mixtures
with at least 50% grass and
• At least 30 feet wide when legumes/forbs
are used alone or legumes make up more
than 50% of the stand.
Increase buffer strip widths as needed to keep
the width of the cropped strips uniform. The
width of the individual buffer strips may vary.
Cropped strips will be of uniform width
between buffer strips and will not exceed 50%
of the slope length (L), used for the erosion
calculation.
Vegetation. Establish buffer strips to
permanent vegetation consisting of grasses,
legumes/forbs, or grass-legume/forb mixtures.
Establish species that are adapted to the site,
and tolerant of the anticipated depth of
sediment deposition.
The buffer strips will have at least 95% ground
cover during periods when erosion is expected
to occur on the cropped strips.
The stem density for grasses and grass-
legume/forb mixtures will be at least 50 stems
per square foot, and for pure legume/forb
stands at least 30 stems per square foot.
Additional Criteria to Reduce Water Quality
Degradation from the Transport of
Nutrients Downslope
Minimum Row Grade. Follow the criteria
outlined in the Additional Criteria to Reduce
Sheet and Rill Erosion.
Maximum Row Grade. Follow the criteria
outlined in the Additional Criteria to Reduce
Sheet and Rill Erosion.
Vegetation. Establish buffer strips to
permanent sod-forming vegetation with stiff,
upright stems.
Width of Strips. Buffer strips will be at least
15 feet wide. Increase the buffer strip widths
as needed to keep the width of the cropped
strips uniform.
The maximum width of cropped strips will be
one-half of the field slope length or 150 feet,
whichever is less.
Arrangement of Strips. In addition to the
buffer strips established on the hillside,
establish a buffer strip at the bottom of the
slope. Make the bottom strip two times the
width of the narrowest buffer strip in the
system.
Additional Criteria to Improve Soil Moisture
Management Through Increased Water
Infiltration
Row Grade. The grade along the upper edge
of the buffer strip shall not exceed 0.2%
Width of Strips. The minimum width will be:
• At least 15 feet wide for strips planted to
grasses or grass-legume/forb mixtures
with at least 50% grass and
• At least 30 feet wide when legumes/forbs
are used alone or legumes/forbs make up
more than 50% of the stand.
Increase buffer strip widths as needed to keep
the width of the cropped strips uniform. The
width of the individual buffer strips may vary.
Cropped strips will be of uniform width
between buffer strips and will not exceed 50%
of the slope length (L), used for the erosion
calculation.
Vegetation. Establish buffer strips to
permanent vegetation consisting of grasses,
legumes/forbs, or grass-legume/forb mixtures.
Establish species that are adapted to the site,
and tolerant of the anticipated depth of
sediment deposition.
The buffer strips will have at least 95% ground
cover during periods when erosion is expected
to occur on the cropped strips.
The stem density for grasses and grass-
legume/forb mixtures will be at least 50 stems
per square foot, and for pure legume/forb
stands at least 30 stems per square foot.
CONSIDERATIONS
General. Several factors influence the
effectiveness of contour farming to reduce soil
erosion. These factors include: 10-year, 24-
hour rainfall in inches; ridge height; row grade;
slope steepness; soil hydrologic group; cover
and roughness; and slope length. Cover and
NRCS, NHCP
September 2014
332 - 3
roughness, row grade, and ridge height can be
influenced by management and provide more
or less benefit depending on design.
Contour farming is most effective on slopes
between 2 and 10 percent. This practice will
be less effective in achieving the stated
purpose(s) on slopes exceeding 10 percent
and in areas with 10-year, 24-hour rainfall over
6.5 inches. The practice is not well suited to
rolling topography having a high degree of
slope irregularity because of the difficulty
meeting row grade criteria.
This practice is most effective on slopes
lengths between 100 and 400 feet. As slopes
lengthen, the volume and velocity of overland
flow are more likely to overwhelm the capacity
of contour ridges and narrow buffer strips to
contain them. Additional residue cover and
other conservation techniques (including
widening buffer strips) will decrease overland
flow velocities, thus increasing the length of
slope on which this practice is effective.
Contour buffer strips are more difficult to
establish on undulating to rolling topography
because of the difficulty of maintaining parallel
strip boundaries across the hill slope or staying
within row grade limits.
Areas of existing or potential concentrated flow
erosion should be protected by conservation
practices such as grassed waterways, water
and sediment control basins, or diversion
terraces.
Where contour row curvature becomes too
sharp to keep equipment aligned with rows
during field operations, increasing the buffer
strip width can help avoid sharp ridge points.
In drainage ways, establishing grassed
waterways at least up to the point of sharp
curvature can allow the equipment to be lifted
and/or turned to meet the same rows across
the turn strip.
Prior to design and layout, remove any
obstructions or make changes in field
boundaries or shape, where feasible, to
improve the effectiveness of the practice and
the ease of performing farming operations.
Prior to layout, inspect the field’s position on
the landscape to find key points for starting
layout or getting the width of one set of strips
(one cultivated and one buffer) to pass by an
obstruction or ridge saddle.
Additional row markers consisting of field
boundaries, hedgerows, fence lines, access
lanes, terraces, etc. may be established as
needed. Permanent vegetated buffer strips
can serve as permanent contour or row
markers to maintain design row grades during
field operations.
Consider re-establishing the native plant
community. Use native species that are
appropriate for the identified resource concern
and management objective. Consider
vegetation that provides multiple benefits to
improve other resources.
Food and Cover for Wildlife and Beneficial
Organisms. The following management
activities may be carried out to enhance
benefits for pollinators, natural enemies of crop
pests, and wildlife benefits as long as they do
not compromise the effectiveness of the buffer
strips:
• Plant herbaceous species that provide
habitat enhancement for the wildlife
species, pollinators, or other beneficial
organisms of concern.
• Add native forbs to the seeding mixture to
increase habitat diversity or to provide
pollen and nectar for beneficial insects.
• Mow the buffer strips every other year or
every third year depending upon
geographical location. The standing cover
provides early and late season nesting and
escape cover for many species of wildlife
displaced from adjacent disturbed areas.
• Delay mowing until after the nesting period
of ground-nesting species, but mow early
enough to allow for regrowth before the
growing season ends.
• To maximize nutrient interception, choose
deep-rooted grasses that will efficiently
remove nutrients that enter the soil profile
within the buffer strip. Harvest hay
regularly to remove surplus nutrients
intercepted
PLANS AND SPECIFICATIONS
Prepare plans and specification for each field
or treatment unit. Specifications shall describe
the requirements to apply this practice to
NRCS, NHCP
September 2014
332 - 4
achieve the intended purpose.
As a minimum, record the following
specification components in an approved
Contour Buffer Strips, 332, Implementation
Requirements document.
• Percent land slope used for conservation
planning;
• The minimum and maximum allowable row
grades for the contour system;
• The designed widths of the buffer strips
• The species to be established in the
buffers strips
• A sketch map or photograph of the field
showing:
• The approximate location of the baselines
used to establish the system;
• The location of stable outlets for the
system ;
• Width of equipment to be used on cropped
rows.
OPERATION AND MAINTENANCE
Conduct all farming operations parallel to the
strip boundaries except on headlands or end
rows with gradients less than the criteria set
forth in this standard.
Time mowing or harvest of buffer strips to
maintain appropriate vegetative density and
height for optimum trapping of sediment from
the upslope cropped strip during the critical
erosion period(s).
Fertilize buffer strips as needed to maintain
stand density.
Mow or harvest sod turn strips and waterways
at least once a year.
Spot seed or totally renovate buffer strip
systems damaged by herbicide application
after residual action of the herbicide is
complete.
Redistribute sediment that accumulates along
the upslope edge of the buffer strip/crop strip
interface as needed. This sediment shall be
spread evenly upslope over the cultivated strip
when needed to maintain uniform sheet flow
along the buffer/cropped strip boundary.
If sediment accumulates just below the
upslope edge of the buffer strip to a depth of 6
inches or more, or stem density falls below
specified amounts in the buffer strip, relocate
the buffer/cropped strip interface location.
Cultivated strips and buffer strips shall be
rotated so that a mature stand of protective
cover is achieved in a newly established buffer
strip immediately below or above the old buffer
strip before removing the old buffer to plant an
erosion-prone crop. Alternate repositioning of
buffer strips to maintain their relative position
on the hill slope. If an established buffer is
removed, a equipment width will be added to
one crop strip and subtracted from another.
Renovate vegetated headlands or end row
area as needed to keep ground cover above
65 percent.
REFERENCES
Foster, G.R. and Seth Dabney, 2005. Revised
Universal Soil Loss Equation, Version 2
(RUSLE2) Science Documentation. USDA-
ARS, Washington, DC. website:
http://www.ars.usda.gov/sp2UserFiles/Place/6
4080510/RUSLE/RUSLE2_Science_Doc.pdf
and
http://www.nrcs.usda.gov/wps/portal/nrcs/main
/national/technical/tools/rusle2/ (verified March
2014)
Renard, K.G., G.R. Foster, G.A. Weesies, D.K.
McCool, and D.C. Yoder, coordinators. 1997.
Predicting soil erosion by water: A guide to
conservation planning with the Revised
Universal Soil Loss Equation (RUSLE).U.S.
Department of Agriculture, Agriculture
Handbook 703. website:
http://ars.usda.gov/SP2UserFiles/Place/64080
530/RUSLE/AH_703.pdf (verified March 2014)
USDA, NRCS. 2011, National Agronomy
Manual, 4th Edition, Washington, D.C.
http://directives.sc.egov.usda.gov/viewerFS.as
px?hid=29606 (verified March 2014)
X. Zhou, M.J. Helmers, H. Asbjornsen, R.
Kolka, M.D. Tomer, and R.M. Cruse. 2014.
Nutrient Removal By Prairie Filter Strips in
Agricultural Landscapes. Journal of Soil and
Water Conservation. Jan/Feb 2014-Vol. 69,
NO. 1.
NRCS, NHCP
September 2014