Switchgrass and Giant Miscanthus Agronomy - Engineering and Science of Biomass Feedstock Production and Provision - page 41

failures than in conventional crops. Poor establishment caused by weed pressure can
delay full production of biomass for 2 or more years [ 34 ]. There are many ways to
minimize weed pressure during the establishment year. Planting into a weed-free
seedbed created by growing a herbicide-tolerant annual crop before planting the
switchgrass will minimize the soil weed seed bank and provide an excellent seedbed.
Frequently, perennial grass-seed germination is very slow, and seedling vigor is not as
good as that of annual grass weeds. Therefore, planting high-quality seed in properly
prepared seedbeds will produce seedlings able to compete with annual weeds (see
Fig. 3.3 ). If a fi eld is expected to have abundant weeds, planting should be delayed in
spring until the fi rst fl ush of weeds has emerged. After weed emergence, a broad-
spectrum herbicide should be sprayed before planting the switchgrass.
Preemergence and postemergence herbicides are effective in controlling and
reducing weed populations during the establishment year (Fig. 3.4 ). Broadleaf
weeds are not considered a major impediment to switchgrass establishment, and
several herbicides are very effective in controlling these weeds, but application
should be delayed until the switchgrass seedlings have reached the four- or fi ve-leaf
stage [ 20 ]. A number of herbicides can be used to prevent and control early grassy
weed growth. Many herbicides used in the forage industry will control weeds, but
not all are labeled for switchgrass establishment, and consulting with local exten-
sion staff or professional advisors for additional information is recommended. In
some environments, fi elds can be infested with weeds even though all recommended
establishment practices have been followed. In these cases, mowing multiple times
during the establishment year at a height slightly above the switchgrass foliage is
recommended to keep the canopy open and reduce weed competition.
Switchgrass seed can be drilled or broadcast into prepared seedbeds. In seedbeds
prepared using conventional tillage practices, either a drill or broadcast seeder with
a cultipacker can be used. Many types of drills, such as grain drills with a small
seedbox, native grass-seed drills, no-till drills, or conventional drills, can be used as
long as the seeding rate and planting depth can be controlled. Drills should have
proper closing wheels, and broadcast seedings should be followed by a cultipacker
to ensure soil-to-seed contact. Broadcast seeding is not suitable in no-till seedbeds,
killed pasture sod, or surfaces with heavy residues. In these cases, switchgrass seed
should be drilled using a heavy no-till drill.
Optimum planting time for switchgrass is in the spring between the corn and soy-
bean planting periods of the region [ 35 , 36 ]. Switchgrass seed can germinate at soil
temperature of 10 °C, but seed germination reaches a maximum between 20 and
30 °C, and seedling growth is optimal when soil temperature reaches above 20 °C
[ 37 - 40 ]. Under optimum soil moisture and temperature conditions, switchgrass seed
germination can begin 3-5 days after planting, but complete emergence can be
delayed by more than a month given unfavorable soil conditions. In areas with regu-
lar spring droughts or fl ooding, or when being planted for conservation, dormant
seeding in late fall/early winter can be used, provided soil temperatures are below
typical germination temperatures and the seed can be incorporated into the seedbed.
The recommended seeding rate for switchgrass is 200-400 PLS m −2 [ 41 ]. The
rate, however, can be reduced to 100 PLS m −2 depending on the seed quality and