Environmental Engineering Reference
In-Depth Information
requirements (Lowenberg-DeBoer and Cherney 1989). Most of the yield reduction associated with
spring harvest was due to harvest losses during baling, suggesting that improvements in harvest
machinery could reduce these losses. Losses in plant biomass during late autumn and winter
are generally associated with translocation of nitrogenous compounds, soluble carbohydrates,
and minerals into underground storage structures and may result in a long-term benefit in a one-
harvest biomass production system, promoting a balance between maximal biomass yield and stand
longevity while providing a more favorable product for energy from combustion.
22.5.4 S
EEd
p
roduction
Management of switchgrass for seed production is based on practices initially recommended by
Cornelius (l950) for the Great Plains, subsequent research in other areas of the United States, and
on anecdotal results of seed producers. Cornelius (1950) reported that cultivated seed production
fields produce more and higher quality seed than from native prairies; row plantings produce more
seed than solid stands; fertilization and weed control are necessary for good seed production; and
spring burning of seed fields usually improves seed yields. In the central Great Plains where most
of the commercially available switchgrass seed is produced, the seed fields are usually planted in
rows spaced about 1 m apart, and are fertilized each spring with 50-110 kg/ha N after the fields
are burned and cultivated to maintain the grass in rows. In Iowa, Cave-in-Rock had higher seed
yields when grown in narrow rows spaced 20 cm apart than in wider rows spaced 1 m apart (Kassel
et al. 1985). In contrast, the cultivars Blackwell and Pathfinder had higher seed yields in wide
rows. Nitrogen fertilizer significantly increases seed yields in Iowa (George et al. 1990). Phosphorus
should be applied when soil tests indicate available soil P is low. Some seed producers irrigate, but
many seed fields in the eastern Great Plains are not irrigated. Switchgrass seed, in contrast to seed
of many native grasses, is heavy and smooth and is easily combined and cleaned with conventional
combines and cleaning equipment (Cornelius, 1950; Wheeler and Hill 1957). Seed is usually
harvested by direct combining. Grazing switchgrass seed fields early in the season reduced seed
yields in the Midwest United States (George et al. 1990; Brejda et al. 1994). Seed yields in an Iowa
study ranged 200-1,000 kg/ha (Kassel et al. 1985). In Missouri, seed yields ranged from 460 to 700
kg/ha (Brejda et al. 1994). The difference in cultivar response was due to differences in lodging.
22.6 carBon, enerGy, and economIc BudGets
The sustainability of switchgrass for bioenergy crops will be determined using carbon, energy, and
economic budgets of the feedstock. Feedstocks must be profitable, have high net energy yields, and
be either neutral or positive with respect to the environment to be viable and sustainable (Casler
et al. 2009).
22.6.1 c
arBon
S
EquEStration
Switchgrass has the potential to extract carbon dioxide from the atmosphere and sequester it in soil.
Frank et al. (2004) reported that soil C increased at a rate of 1.01 kg C/m
2
per year, and switchgrass
plantings in the northern Great Plains have the potential to store significant quantities of soil organic
carbon (SOC). Liebig et al. (2005) reported that switchgrass grown in North Dakota stored 12 Mg/
ha more SOC in the 30- to 90-cm depth than a cropland paired field experiment. They concluded
that switchgrass effectively stores SOC not just near the soil surface, but at greater depths where C
is less susceptible to mineralization and loss. Lee et al. (2007) reported that switchgrass grown in
South Dakota CRP lands stored SOC at a rate of 2.4-4 Mg/ha per year at the 0- to 90-cm depth.
In a 5-year field study conducted on 10 farms in Nebraska, South Dakota, and North Dakota, SOC
increased significantly at 0-30 cm and 0-120 cm soil depths, with an average increase in SOC of
1.1 and 2.9 Mg C/ha per year, respectively (Liebig et al. 2008). However, they noted that change in
