Roadside Revegetation

IMPLEMENTATION GUIDES
Duration in Slurry – The longer seeds are mixed in the slurry tank, the greater the potential
for breakage. Kay and others (1977) found that after 20 minutes of agitation, seed germination
decreased significantly (Figure 10-100). For this reason, it is important to add seeds immediately
before application.
Seed Moisture – As a general rule, moistened seeds have less potential for breakage than
dry seeds because they are more flexible when impacted. Kay and others (1977) found that
soaking seeds for 1.5 days prior to application significantly increased germination over dry
seeds (Figure 10-100). Longer soaking periods (4 days) had negative effects on germination
because radicles were emerging and were damaged with mixing.
Soaking seeds prior to hydroseeding will unfortunately initiate seed germination, which is not
usually desirable for hydroseeding projects. Pill and Nesnow (1999) suggest seed priming as
an alternative to soaking. Priming is a seed treatment that partially moistens seeds without
initiating seed germination (Pill and others 1997). Seed is mixed at one part seed to 10 parts
moist vermiculite (although peat could be used as a substitute) and stored at cool temperatures
for up to 10 days prior to hydroseeding.
Hydraulic Mulch – Hydroseeding without hydraulic mulch can increase seed damage (Kay
1972a, 1978). Using a minimum rate of 500 lb/ac hydraulic mulch is suggested for protecting
seeds (Kay 1978).
Nozzle Type and Nozzle Position – Shooting slurry straight at the soil in close range can
damage seeds. The impact at high speeds can cause seed coats to break. As one hydroseeding
operator describes the action, “we just shove that seed right smack in the ground with a lot
of force...the gun was slamming straight to it” (Brzozowski 2003). Describing this action to a
Forest Service seed extractory specialist, his reaction was, “that can’t be good for the seed”
(Barnar 2007). In the seed production and seed extraction businesses, handling seeds carefully
is a high priority. This attitude and practice should not stop with the seed producers, but
follow through to the application of seeds. One application practice that could reduce seed
damage is to aim nozzles so the slurry is not hitting the soil surface with full force at close
range. Arching the slurry stream so the spray hits with lower force is more desirable. Using
less pressure or lower pressure nozzles, such as fan nozzles, can also reduce seed damage
(Figure 10-101). Some soils are very loose or powdery after construction, which can cushion
the seeds, as opposed to very compacted surfaces. Seeds applied to these surfaces can be
buried under the loose soil when the slurry is shot straight at the surface, offsetting the effects
of seed breakage and increasing germination potential (Mast 2007).
Fertilizers – Adding fertilizer to the slurry can reduce germination of certain species due to
the effects of fertilizer salts on seed imbibition, or uptake of water (Brooks and Blaser 1964;
Carr and Ballard 1979; Brown and others 1983). This is not just a problem when seeds and
fertilizers are mixed together in the slurry tank; it can also negatively impact the seeds after
they are applied to the soil surface and before the first rains dilute the surrounding salts.
Effects of fertilizer salts will be more detrimental on sites with low rainfall. Carr and Ballard
A
B
Figure 10-101 | Hydraulic seeder nozzles
Hydraulic seeders are equipped with several
types of nozzles. The nozzle shown in photograph
(A) shoots long, high pressure, streams
while the fan nozzle shown in (B) spreads the
slurry out for closer applications
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