C. L. Dewald, Jim Henry, Steve Bruckerhoff, Jerry Ritchie, Seth Dabney, Dan
Shepherd, Joel Douglas, Dale Wolf. USDA, ARS, SCS
Soil erosion is a major problem around the world (3). An economical method to slow runoff
and reduce soil loss is stiff, erect, densely-tillered narrow grass hedges. Such grass
hedges are widely used in India, the West Indies, and other countries to reduce soil loss
(10). The concept of using grass barriers for erosion control was proposed by USDA Soil
Conservation Service (SCS) about 40 years ago in the United States but for a variety of
reasons was not adopted.
In recent years there has been a renewed interest in the use of narrow stiff grass hedges
as a conservation practice (7). Research has been done on application of grass barriers to
reduce water (4) and wind (1, 11) erosion. Research has shown grass hedges to slow runoff,
trap sediment, prevent gullying (4, 9), and enhance terrace formation (1). They are an
inexpensive, biological, conservation technology compatible with current tillage systems
(8).
In 1991 the USDA Agricultural Research Service (ARS) and the USDA Soil Conservation
Service (S CS), now the Natural Resource Conservation Service (RCS) along with several
universities initiated a program to study grass hedges to control runoff and reduce soil
loss. In 1994, the SCS initiated a three-year evaluation of a national interim practice
standard for the design and implementation of grass hedges as an accepted conservation
practice.
Grass hedges differ from other common types of grass strips (i.e. buffer strips, filter
strips) because they are narrow, planted with stiff, erect grasses, and capitalize on,
rather than minimize, the formation of berms by deposited sediment. A dense uniform stand
of coarse stems slows concentrated runoff, causing backwaters as deep as 12 to 16"
and allows time for deposition of eroded sediments. The deposited sediment fills in low
spots in fields so that future runoff is more broadly dispersed and less erosive. The
general concept of this technology is that narrow rows of grass hedges are planted in
parallel lines across and perpendicular to the dominant slope of the field (7) (Fig. 1).
The design, spacing and lateral extent for vegetative barriers in concentrated flow zones
depends on anticipated runoff rates, topography, and other factors which have been
detailed previously (4, 7).
Factors which influence the success of grass hedge plantings includes selection of the
proper grass, use of high quality seed, proper seedbed preparation, precision planting,
optimum timing and sound management practices during and following establishment.
Grass selection
Research has shown that a variety of perennial grasses that have coarse stems will work as
hedges if they can be established as a uniform and dense hedge, and are tolerant of silt
deposition. Warm-season grasses are probably better candidates for hedges because they are
generally more robust and tend to have stiffer stems and, increased tillering within the
hedge than most cool-season grasses. Grass hedges should consist of stiff, erect,
perennial grasses which are adapted to local soil and climatic conditions. Grass barriers
must have sufficient stem strength to remain erect against expected water flows.
Suitable barrier plants must satisfy several criteria. They must be tolerant to: (a)
herbicides used on adjacent cultivated crops; (b) partial shading from cultivated crops;
(c) inundation by sediment; (d) local climatic extremes (wetness, drought, freezing
temperatures, etc.); and, (e) easily established from available materials; (f) long lived
and manageable as a narrow strip; (g) non-weedy and not too competitive with adjacent
cultivated crops; and ('1) relatively tolerant to defoliation if crop residues are grazed.
Switchgrass (Panicum virgatum L.) and eastern gamagrass (Tripsacum dactyloides L.) are two
warm season, perennial native, non-weedy species with potential as hedges in much of the
United States.
Switchgrass has a wide area of adaptation, determinate seeding habit, smooth (non-chaffy)
seed characteristics for ease of handling, and prolific' production of coarse durable
vegetation making it a leading candidate for use in grass hedges for erosion control.
Research on switchgrass improvement has been conducted for many years and has resulted in
no less than a dozen released improved varieties which has increased the adaptation
potential of the species considerably (12). State Extension and/or local NRCS personnel
should be consulted to determine the variety best adapted to a particular site and
situation.
Eastern gamagrass has recently received considerable attention for use in grass hedges for
erosion control. Problems inherent to the species, including indeterminant low seed
production, seed dormancy and resulting problems in stand establishment (2) have slowed
the progress in eastern gamagrass variety development, but the erosion resistance
potential of the grass merits further research. The crowns of eastern gamagrass are formed
by a proliferation of compact shoots consisting of vegetative and reproductive tillers in
various stages of development (5). Shoots are interconnected through several tiller
generations by a thick (1/2 to 1") woody proaxis (stembase) chain network which
remains intact for several years acting as a considerable deterrent to erosion. The
dynamic crown has the capacity to elevate coarse aerial foliage above sediment coverage
and to anchor the plant in place with stout (1/16 to 1/8" diameter) brace roots.
Seedbed preparation
Poor seedbed preparation is a major cause of stand failures in grass plantings and
therefore seedbed preparation should be planned and initiated well ahead of planting.
Methods of seedbed preparation (the cultural treatments needed to produce a suitable
medium for optimum germination and seedling emergence) will depend largely on the
condition of the site to be seeded.
No-till seeding can be ideal, provided the seedbed allows the placement of seed at an
optimum depth and the planting operation is capable of firming the soil above and around
the seed to obtain good seed-soil contact which is necessary for retention of soil
moisture in direct contact with seeds during the germination process.
No-till seeding into areas with excessive surface residues (50% or more of the soil
surface covered) or with weed competition is not recommended. Excessive surface residues
and weed competition can often be reduced by mechanical means, burning and/or the use of
broad spectrum herbicides prior to grass seeding. In cases where such remedial practices
are not' feasible it will be necessary to resort to tilled seedbed preparation methods.
Tilled seedbeds have the same rigid requirements for, successful grass hedge establishment
as outlined for no-till seedbeds. An ideal seedbed will result in optimum
soil-moisture-seed relationships during seed germination and early seedling establishment.
A firm smooth soil surface, not excessively compacted, is required to facilitate precision
planting and to optimize soil-moisture-seed relationships. The disk, offset or tandem, is
probably the most common tool used for seedbed preparation when site conditions allow for
its effective use. Harrowing and cultipacking following disking helps smooth and firm the
seedbed.
Excessively loose and rough seedbeds hamper seeding success because seeding depths cannot
be controlled accurately. Soils should not be worked when excessively wet, and any
operation which results in the formation of clods should be avoided. Grass seeds are small
and must be planted relatively shallow in order for the energy stored within the small
seed to power the seedling emergence process. Firm seedbeds are essential as loose porous
seedbeds do not provide adequate contact between seeds and the underlying soil water
needed to ensure germination of seeds placed near the soil surface.
Use good quality seed
The use of good quality seed is essential to allow for precision planting and to help
ensure success of grass hedge establishment. Seed should be purchased from a reputable
seed source on a pure live seed (PLS) basis. The seed tag should list the percentage
purity, other crop, inert, weed seed, germination, hard seed, dormant seed, and total
germination of the product. It is very important to plant seed with high purity as this
reduces the percentage of detrimental materials, (i.e., inert which interferes with
planting efficiency, and other crop and weed seed which can compete with the grass
seedlings during establishment). Most seed tags include percentage hard and/or dormant
seed which are seed determined to be viable, but which fail to germinate following
standardized preconditioning treatments. Percent germination, firm seed and/or dormant
seed are summed and reported as total germination. Pure live seed is determined by
multiplying the decimal value of % purity by % total germination. A high percentage PLS is
an indication of over all seed quality.
Stratification by moist prechill occurs in nature as seeds fall from the grass plant in
the Fall and lay dormant on or in the soil throughout the winter until soil temperatures
are conducive for germination the following Spring. The natural stratification process is
short circuited when seeds are harvested from the plant, stored dry over winter and
planted in warm soil the following spring. In laboratory tests seeds of switchgrass and
eastern gamagrass are subjected to standardized moist prechill (stratification) treatments
designed to break dormancy and enhance germination. A do-it-yourself germination test that
measures actual germination without artificial stratification is often more meaningful
than laboratory tests. A "ragdoll" test can be conducted by placing 100 seed on
the right half of a wet paper towel, folding the left half of the towel over the seed, and
rolling it into a tight tube. Excess water should be allowed to drain from the ragdoll
which can then be sealed in a plastic sandwich bag to prevent excessive drying. The
ragdoll should be kept in a warm (70-85� F) place until germination counts are made 7
days later. Placing some seed you know will germinate (alfalfa, millet, clover) in a
similar ragdoll will confirm that the test conditions are suitable for proper germination.
The number of seed which germinate in the ragdoll is equivalent to actual % germination
and can be multiplied by % purity, expressed as a decimal value, to calculate pure actual
germination (PAG). Pounds of seed/A on a PAG basis can be calculated by dividing the
laboratory PLS by the obtained PAG and multiplying by lb PLS recommended per acre. This
usually amounts to an increase in seeding rate which gives added insurance for rapid
establishment of a thick grass stand.
Eastern gamagrass seeds consist of grain (caryopses) enclosed in a hard woody fruit case
which protects the grain and inhibits germination of the grain until stratification is
induced (2). The protective fruit case makes up about 70% of the total weight of good
quality gamagrass seed and a much higher percentage of poor quality seed weights. Good
quality eastern gamagrass seed should have at least 95% purity, a PLS of 80% or better and
6000 or less seeds per pound. Stratified seed (i.e., moist prechill at 35 to 45� F for at
least 6 weeks) should be purchased from reputable dealers to increase the success of grass
hedge establishment.
When to plant
Spring planting should be done as soon as the soil temperature warms up to the point
required for optimum germination of the seed being planted and if possible just prior to
the greatest probability of substantial or prolonged rainfall. In some areas these two
factors may not coincide, thus a compromise may be necessary.
Switchgrass and eastern gamagrass should be planted when soil temperatures stabilize in
the range of 65 to 80� F at a 1" depth-below the soil surface. Faster germination
and seedling emergence will occur when soil temperatures are near the upper limits of the
temperature range (80 to 85� F) when soil moisture is not limiting. Planting dates will
vary depending on locations but are generally between March 15 and May 15 in the South and
May 1 to June 15 in the northern states. In relation to other crops, the warm season
grasses should be planted later than corn, but prior to cotton or soybean planting time.
In general, later planting dates will allow more time for weed emergence and weed control
prior to grass hedge planting, but this must be considered in relation to timing of
rainfall probabilities. In more arid areas it may be better to plant as soon as the
1" soil temperature reaches 65� F; whereas later plantings are preferable in more
humid zones.
Planting rates
Planting rates for grass hedge establishment should be two to four times more than rates
recommended for pasture plantings because grass hedges are planted in narrow strips with
their function requiring a rapid development of a dense stand of grass.
Switchgrass planting rates should approximate the critical area stabilization rate (i.e.
about twice that of pasture plantings) which translates to a minimum of 44 potential
seedlings per square ft. of the planted area. This is equivalent to 8 to 10 lb. PLS per
acre, but if a ragdoll test shows that actual germination is overstated on the seed tag,
the seeding' rate should be adjusted upward accordingly. Grass hedges occupy only a small
percentage of the total field area so that increased seeding rates are usually cost
effective.
Eastern gamagrass should be planted at the rate of 10 to 12 lb. PLS/row mile of hedge and
lb./A will vary depending on the row spacing to be used. The 10 to 12 lb. PLS/row/mile
will be equivalent to 9 to 13 pure live seed per linear ft of row. The amount of seed
needed can be determined by multiplying the miles of hedge rows to be planted times 10 to
12 lb. PLS (i.e., 1 mile of 2 row hedge 1 x 2 x 10 to 12 = 20 to 24 lb. PLS needed).
Planting procedures
Width of grass hedges should be a least 1 to 2 ft. wide to a maximum of five ft. Wider
strips can be narrowed down with cultivation once the hedge plants are well established
(Fig. 2 and 3). A single row of a dense grass stand is usually adequate except in
concentrated flow areas where at least two rows are required.
Switchgrass is usually drill seeded in rows 6 to 8" apart at a depth of 1/4 to
A". Seed placement should be uniform in rows with drills having a small seed
attachment. Drills equipped with double-disk openers with proper depth bands facilitate
placement of seed at the proper depth (Fig. 4). The depth bands should be secured to the
disk openers at a distance of _" from the cutting edge of the disk. Tension on the
disk openers should be such that the depth bands roll on the soil surface and do not
become submerged nor ride above the soil surface. Packer wheels on the drill which firm
the soil over the planted seed are also very beneficial. Drag chains, though inferior to
packer wheels, may also be used to cover and firm the soil around the seed, and a
cultipacker or roller may be used immediately following planting if needed to firm the
soil.
Stratified seed of eastern gamagrass should be planted 1 to 1-1/2" deep. Planting in
deep furrows in soils subject to washing should be avoided as seed can be covered too
deep. Planting shallower than 1" will have less favorable moisture - seed relations
and emergence may be delayed. Row planters (corn, cotton, peanut, etc.) are easily
adjusted to plant gamagrass in rows. The row planter furrowing out shovels or disk openers
can be set to push away dry surface soil and insure the placement of the grass seed in a
moist environment. The covering device should be set to cover the seed with moist soil and
the packer wheel adjusted to firm the soil over the seed row. Stratified seed has
increased weight due to extra moisture content and calibration is best done by counting
the seed to determine the number dispensed per linear ft of row (i.e. 9 to 13 pure live
seed/linear ft of row is recommended).
Management practices
Washout or other problems may cause voids or skips in the grass hedge which require
replanting. Reseeding by hand broadcasting and covering the seed by a hand rake may be
practical for reseeding small voids. In concentrated flow areas, replanting washouts with
vegetative transplants may be more effective than reseeding as transplants provide quicker
cover and provide protection sooner than seedlings.
Both switchgrass and eastern gamagrass can be established vegetatively from crown material
transplanted during the dormant season prior to spring green-up (6). Propagules can be
obtained
from adjacent established plants by splitting off portions of crown material with a shovel
and replanting the crown material in the voids. Individual transplanting units of
switchgrass should have at least 4 to 5 viable shoots (stem base) while eastern gamagrass
should have at least 3. The transplants should be spaced no more than 6" apart in the
row to create a dense hedge.
Fertility levels of phosphorus (P) and potassium (K) which promote good growth of the
companion cultivated crop will be adequate for grass hedges. Soil tests are required to
determine P and K needs if they haven't been applied recently in the crop management
program. Nitrogen ~) should not be applied until after a good grass stand is obtained and
plants have reached a height of at least 4" because N promotes weed growth and
competition. After the grass is established it should be fertilized annually with 60 lb
actual N/A preferably in April or early May.
Mowing at a 10 to 12" height is a good practice for control of tall weeds during
establishment and for hedge maintenance thereafter. Usually an early-summer mowing is
needed to prevent the grass hedge from lodging on the adjacent crop rows. Grass hedges
should not be mowed shorter than 10-12" as this is a minimum height for hedge
efficiency and lower cuttings during periods of active growth may severely reduce the
vigor of the grass.
Burning can be an effective tool for grass hedge management, but the timing of burning is
critical. Winter burning is not recommended as the dormant hedge still maintains a high
degree of its water impounding function during this period (Fig. 5). Burning just prior to
spring greenup of the hedge would reduce the time that the hedge would lose effectiveness
and should be considered in relation to period of probable runoff. Burning stimulates
grass hedge tillering and vigor, but caution in its use is recommended.
Summary
Grass hedges can be a relatively economical means to slow runoff water and reduce soil
loss. There are several factors which will influence the success of grass hedge
establishment including grass selection, seed quality, seedbed preparation, planting
procedures, timing and management practices during and following establishment. Failure to
consider any one of these factors may jeopardize the success of grass hedge establishment.
Grass hedge establishment is not simple nor easy, but the rewards from a well established
grass hedge should offset the effort. Good Luck.
REFERENCES CITED
1. Aase, J. K. and J. L. Pikul, Jr. 1995. Terrace formation in cropping strips protected
by tall wheatgrass barriers. J. Soil and Water Conservation 50:110-112.
2. Ahring, R. M. and H. Frank. 1968. Establishment of eastern gamagrass from seed and
vegetative propagation. J. Range Manage. 21:27-30.
3. Brown, L. R. and E. C. Wolf. 1984. Soil erosion: the quiet crisis in the world economy.
Worldwatch Paper #60, 51 pp.
4. Dabney, S. M., K. C. McGregor, L. D. Meyer, E. H. Grissinger and G. R. Foster. 1993.
Vegetative barriers for runoff and sediment control. pp.60-70. In J. K. Mitchell (ed.).
Integrated Resource Management and Landscape Modification for Environmental Protection,
American Society of Agricultural Engineers, St. Joseph, MI.
5. Dewald, C. L. and V. H. Louthan. 1979. Sequential development of shoot system
components in eastern gamagrass. J. Range Manage. 32:147-151.
6. Dewald, C. L. and P. L. Sims. 1981. Seasonal vegetative establishment and shoot
reserves of eastern gamagrass. J. Range Manage. 34:300-304.
7. Kemper, D., S. Dabney, L. Kramer, D. Dominick and T. Keep. 1992. Hedging against
erosion. J. Soil and Water Conservation 47:284-288.
8. McGregor, K. C. And S. M. Dabney. 1993. Grass hedges reduce soil loss on no-till and
conventional-till plots. Proceedings Soil Conservation Tillage Conference for Sustainable
Agriculture, Monroe, LA. pp. 16-20.
9. Meyer, L. D., S. M. Dabney and W. C. Harmon. 1994. Sediment-trapping effectiveness of
stiff-grass hedges. American Society of Agricultural Engineers Paper No.94-2186, American
Society of Agricultural Engineers, St. Joseph, MI.
10. National Research Council. 1993. Vetiver grass: a thin green line against erosion.
National Academy Press, Washington, DC. 169 pp.
11. Siddoway, F. H. 1970. Barriers for wind erosion control and water conservation. J.
Soil and Water Conservation 25:181 - 184.
12. Vogel, K. P., C. L. Dewald, H. J. Gorz and F. A. Haskins. 1985. Improvements of
switchgrass, indiangrass, and eastern gamagrass: Current status and future. Proc. Soc.
Range Manage. Symp. pp.159-170. Soc. Range Manage., Denver, CO.
Figures
Figure 1. The general concept of grass hedge technology is the planting of narrow rows of
hedges in parallel lines across and perpendicular to the dominant slope of the field.
Figure 2. Switchgrass in this Missouri cotton field produced a dense stand within two
months of planting. The hedge can be narrowed down by cultivation in subsequent years if
desired.
Figure 3. A single row of switchgrass in its second growing season gives adequate erosion
protection in an Iowa corn field.
Figure 4. Grass drills with double-disc openers equipped with depth bands are used to
place seed uniformly at desired depths.
Figure 5. Dormant grass hedges continue their erosion control functions in winter months
between cropping seasons.