Environmental Engineering Reference
In-Depth Information
Great Plains of the United States (Sanderson and Wolf 1995; Mitchell et al. 1997, 2001). In the Central
Great Plains, photoperiod as measured by DOY was more predictive of physiological development
than GDD, indicating that photoperiod is the primary determinant of switchgrass development but
photosynthesis or heat units can modify the developmental response (Mitchell et al. 1997).
A population of switchgrass plants will have populations of tillers at different stages of
development (Mitchell et al. 1997). Genetically broad-based populations will have some plants at
anthesis over a 3-week period (Jones and Brown 1951). Florets in an individual panicle will be
undergoing anthesis for up to 12 d (Jones and Newell 1946). Peak pollen shedding periods are from
10:00 to 12:00 h or from 12:00 to 15:00 h depending upon environmental conditions (Jones and
Newell 1946). Heading dates for cultivars are typically expressed as population means. Because
flowering time varies among individual genotypes, the development of ripe seed is also variable
within a population or cultivar.
The stem bases, roots, and rhizomes are the primary sites of nonstructural carbohydrate storage.
Starch is the primary and most dynamic nonstructural carbohydrate in switchgrass stem bases and
rhizomes (Smith 1975). Nonreducing sugars, primarily sucrose, are secondary in importance to
starch and fluctuate in a similar manner during the growing season. Total nonstructural carbohydrates
(TNC) concentrations in the stem bases of unharvested plants are greatest at the beginning and
end of the growing season. Stem base TNC concentrations reach the lowest levels at the time of
tiller elongation or when regrowth is initiated following harvest (Smith 1975). A recent fertilization
study in which N concentration of biomass was monitored indicates that switchgrass may actively
transport N and nonstructural carbohydrates from above ground biomass to stem bases and roots
after anthesis but before a killing frost (Vogel et al. 2002a). Harvest time is critical for adequate
survival of switchgrass swards, with consistently early harvests reducing switchgrass stands, most
likely due to inadequate time for cycling of nitrogen and soluble carbohydrates to storage organs
(Casler and Boe 2003).
Switchgrass requires the establishment of a symbiotic relationship with arbuscular mycorrhizal
fungi (AMF) in its roots to become established and persist (Brejda et al. 1998). Rhizosphere
microflora from numerous native prairies and old seeded stands of switchgrass were effective in
enhancing seedling growth of switchgrass in greenhouse trials (Brejda et al. 1998). A field study
on two different soils demonstrated that indigenous AMF in cultivated fields of the central Great
Plains establish a symbiotic relationship with switchgrass and that inoculation offers little potential
to increase switchgrass production unless the soils have been severely degraded (Brejda 1996).
Significant interactions between AMF isolates and soil types suggest some differential adaptation
of AMF isolates to different soils (Clark et al. 2005).
Switchgrass is relatively drought tolerant with a deep root system likely contributing to its ability
to draw water from deep aquifers. Water-use efficiency (WUE) of switchgrass was 1.8-3.6 mg
biomass/g water across several soils and nitrogen rates in Pennsylvania (Stout 1992). Switchgrass
WUE increased by 30% with an increase in N fertilizer from 0 to 84 kg N/ha. In that study, the
WUE of switchgrass was 5.7 times greater than the WUE of orchardgrass (
Dactylis glomerata
L.).
In the Great Plains of the United States, the WUE of switchgrass ranged from 3.5 to 5 mg biomass/g
water across several locations (Kiniry et al. 2008). The WUE of switchgrass was 1.8-5.0 times
greater than the WUE of maize used for grain production, but similar to the WUE of maize biomass
production (Kiniry et al. 2008).
22.5 manaGement
22.5.1 E
StaBliShmEnt
Recommended seeding rates are 200-400 pure live seeds (PLS) per m
2
(Vogel 1987). Establishment-
year stands with 20 or more plants/m
2
will produce harvestable forage the year of establishment if
weeds are controlled and can be in full production the year after establishment (Vogel 1987; Vogel
