Switchgrass and Giant Miscanthus Agronomy - Engineering and Science of Biomass Feedstock Production and Provision - page 39

Fig. 3.3 Switchgrass stands during the establishment year show the importance of seed quality. The
plots were planted with the same cultivar coming from different seed lots. A high-quality seed lot
ensures seedling vigor and produces seedlings that outcompete annual weeds ( right side of photo)
Switchgrass yields can vary based on the production region and ecotypes and
cultivars grown. Based on a recent meta-analysis of 106 sites from 45 studies cover-
ing the eastern two-thirds of the USA and southeastern Canada, the average yield of
upland and lowland switchgrasses across all regions was 6.6 ± 3 Mg ha −1 during the
establishment year [ 27 ]. The second- and third-year biomass yields increased from
9.1 ± 5.5 to 10.9 ± 5.2 Mg ha −1 , respectively. During the post-establishment years,
biomass yields of lowland ecotypes (11.1±6.1 Mg ha −1 ) were greater than for
upland ecotypes (6.7±3.2 Mg ha −1 ). Among study sites, the highest yield
(13.4 ± 4.5 Mg ha −1 ) was observed in lower central regions (US hardiness zones 6
and 7) and the lowest yield (7.3 ± 3.1 Mg ha −1 ) was observed in northern regions
(US hardiness zones 3 and 4).
Switchgrass seed quality can be reduced by the presence of inert materials and
weed and unviable seeds, which can affect seedling vigor and establishment speed.
Seed quality tests that determine viability and purity should be examined before the
seed is purchased to ensure the best-possible establishment (Fig. 3.3 ). Unlike soy-
bean ( Glycine max (L.) Merr.) or corn ( Zea mays L.) seed, grass-seed quality and
sales are based on percent Pure Live Seed (PLS), which is calculated by
PLS (%) = [% seed purity X % viable seed]/100; (% viable seed = % dormant
seed + % germination) [ 28 ].
The laboratory-derived seed purity, viable seed, dormant seed, and germination
percentages are available on the seed tag. It is important to note that the percent PLS
information on seed tags can overestimate the percent of actual seed germination in