Switchgrass and Giant Miscanthus Agronomy - Engineering and Science of Biomass Feedstock Production and Provision - page 40

the fi eld because PLS calculations include hard, dormant seeds, which do not
germinate immediately. For this reason, Mitchell and Vogel [ 29 ] suggest determin-
ing seeding rates based on the number of germinated or emerged seeds per gram of
seed to reduce the risk of establishment failure.
Seed dormancy is a major factor in delayed seed germination and reduced seed-
ling vigor and often results in poor establishment [ 20 , 22 ]. Switchgrass seed dor-
mancy is a natural mechanism for limiting the germination of late season-produced
seed until the following spring, which normally improves seedling survival [ 30 ].
Postharvest ripening can naturally break seed dormancy. Vogel [ 31 ] reported that
seed dormancy is greatly reduced when seed is stored for a year or more at room
temperature, but viability will be decreased when seed is stored for more than 2
years at room temperature. Other methods used to break seed dormancy or increase
germination, such as cold stratifi cation or chemical treatments, are not recom-
mended for general switchgrass production.

3.2.2 Establishment

Switchgrass can be grown in a wide variety of soil types and conditions, but per-
forms best in well-drained soils with pH levels between 6.0 and 8.0, potassium
levels of at least 200 kg ha −1 , and phosphorus levels of at least 22 kg ha −1 [ 14 , 22 ].
Since switchgrass seed is small and fi eld germination is slower than for many con-
ventional crops, proper seeding depth, weed control, and seed-to-soil contact are all
critical for successful switchgrass establishment [ 20 ]. Shallow seeding depth is
critical for warm-season grass-seedling emergence [ 32 ]. To maximize seed germi-
nation, switchgrass seeds should be planted into a fi rm seedbed as planting in loose
soil can result in seeds being planted too deeply, limit soil-to-seed contact, and
ultimately result in a poor stand [ 14 ]. Switchgrass seed should be planted at depths
between 5 and 20 mm in fi ne-textured soils and 30 mm in coarse-textured soils [ 14 ].
Proper fi eld preparation is required to maximize seed germination and seedling
growth and will vary depending on the previous crop and residue conditions. No-till
planting into soybean stubble or fi elds with minimum residues provides the best
opportunity for successful establishment, but planting into fi elds previously grow-
ing other crops can also be successful if the residue is incorporated and weed growth
is prevented [ 33 ]. Fields with heavy surface residues, such as often occurs follow-
ing maize, require tillage practices to incorporate residues. If tillage is needed to
clean the soil surface, a cultipacker or roller should be used to fi rm the soil prior to
planting. Planting switchgrass on land previously in sod or pasture requires control-
ling the existing vegetation and incorporating the heavy residue from aboveground
vegetation and roots and rhizomes belowground. In this case, nonselective herbi-
cides to control existing vegetation, along with tillage practices to control heavy
surface and subsurface residues, are necessary.
One of the most important factors for successful switchgrass establishment is weed
control. Weed competition in new switchgrass plantings can cause more establishment