Switchgrass and Giant Miscanthus Agronomy - Engineering and Science of Biomass Feedstock Production and Provision - page 44

and a single harvest at anthesis produces maximum biomass [ 42 , 44 , 52 ]. The quantity
of switchgrass biomass continuously decreases until completion of senescence in late
fall, and the yield losses range from 10 to 20 % depending on the growing regions
and weather [ 44 , 52 ]. Harvesting at peak standing crop unnecessarily removes nutri-
ents and negatively impacts stand health and longevity [ 42 ]. In some cases, biomass
can be harvested at peak standing crop to take advantage of high market prices or for
emergency hay production. Flexible management, including extra N-fertilization or
alternating harvesting timing, may be required to maintain stand health [ 42 ].
Even though delaying harvest reduces biomass yield, harvesting after a killing
frost minimizes input costs, increases feedstock quality through nutrient recycling,
and maximizes stand sustainability [ 14 , 42 ]. Early harvesting has a negative impact
on switchgrass stand and results in biomass with signifi cantly higher N concentra-
tions and ash content compared to biomass harvested after a killing frost. In general,
the best harvest management practice for switchgrass is a single harvest following
senescence, or several weeks after a killing frost, which allows N and other nutrients
to translocate from the shoot into the belowground biomass for winter storage and
promotion of new growth the following spring. There are several benefi ts of delay-
ing biomass harvest until spring such as signifi cant reduction of ash in biomass,
improved wildlife habitats, capturing snow to add moisture to the root zone, and
distribution of farm labor and storage facilities over winter. However, some biomass
yield loss is expected when overwintering in the fi eld. Moreover, the impact of
weather on harvesting operations must also be considered as it may limit fi eld acces-
sibility due to severe weather conditions such as snow and fl oods.
Depending on the length of growing season and precipitation quantity and distri-
bution, two harvests per season can be considered. However, a two-harvest system
is not recommended unless two harvests produce signifi cantly more biomass and
compensate for the increased costs of two harvests.
Chapter 5 in this topic discusses the harvesting operation, including the issues
with machine design and operation. It is, however, important to note that many fac-
tors highlighted here will have an impact on the harvesting operations as discussed
in Chap. 5 .

3.3 Giant Miscanthus

The genus Miscanthus is comprised of 11-12 species, most of which are native to
eastern and southeastern Asia [ 53 ]. Jones and Walsh [ 54 ] wrote that within the
genus, M. sinensis , M. saccharifl orus , and M . × giganteus have the greatest potential
for use as bioenergy crops. All three of these grasses have been planted as landscape
ornamentals and are being considered for bioenergy production in the USA; in Asia,
M. sinensis has been grazed in Japan [ 55 ] and M. saccharifl orus used by the cellu-
lose industry in China [ 53 ]. This chapter will primarily focus on M . × giganteus .