Switchgrass (Panicum virgatum L.)—a perennial, warm-season (C4) species—evolved across North America into multiple, divergent populations. The resulting natural variation within the species presents considerable morphological diversity and a wide range of adaptation. The species was adopted as a crop—initially as a forage—only in the last 50 yr. Its potential uses have recently been expanded to include biofuels. Management of switchgrass for biofuels is informed by an understanding of the plant's biology. Successful establishment requires attention to seed dormancy and weed control as well as proper depth and date of planting. The plant's growth rate is closely tied to temperature, but timing of reproductive development is linked to photoperiod. Accordingly, the period of vegetative growth can be extended by planting lower-latitude cultivars at higher latitudes. This strategy may provide a yield advantage, but cold tolerance can become limiting. Switchgrass is thrifty in its use of applied N; it appears a...

The Biology and Agronomy of Switchgrass for Biofuels

Information is lacking on the nitrogen content of switchgrass ( Panicum virgatum L.) biomass from different genotypes and management systems. Nitrogen removed in the biomass would be important in determining fertilization practices and biological degradation. Six switchgrass entries were grown for biomass yield under two harvest systems, one-cut: cut once near the end of October, and two-cut: cut in early summer and near the end of October. Dry matter yield, N concentration, and N content of biomass were determined for five years. More N was usually removed in the two-cut system than in the one-cut system. Nitrogen removed in the biomass exceeded N applied under the two- cut system in all years except one year with a severe summer drought. In the one-cut system N removed was less than applied in all years except when no N was applied in the last year. Nitrogen concentration was higher in the summer harvest than the fall harvest of the two-cut system. Nitrogen concentration in the fall harvest was lower for the one-cut than the two-cut system. Differences in N removed between harvest systems reflected the low N concentration of the fall harvest of the one-cut system and the higher N concentration in the summer harvest of the two-cut system.

Nitrogen removal in switchgrass biomass under two harvest systems

Optimizing feedstock production from switchgrass (Panicum virgatum L.) requires careful matching of genotype to environment, especially for southern U.S. regions. Nine genotypes from four combinations of ecotype and morphological type were harvested once yearly in autumn for 3 or 4 yr at five locations across Texas, Arkansas, and Louisiana that varied in latitude and precipitation. Genotypes were evaluated for dry matter yield (DMY), plant density, tiller density, lodging, and rust (caused by Puccinia spp.) infection. Genotype x environment (GxE) interactions were identified for most traits. Biomass yield of all genotypes tended to increase with latitude, but lowland morphological types may have been more sensitive than upland morphological types to differences in moisture availability. Yield (5.82 vs. 14.97 Mg ha -1 , respectively) and persistence (final stand density, 3.99 vs. 5.96 plants m -2 ) were lower for upland than for lowland genotypes, particularly at higher rainfall and more southern sites. Lowland genotypes were often able to compensate for stand thinning by increasing individual plant size, but upland genotypes were not. Lodging and rust scores were higher for upland than for lowland genotypes. Yield (13.65 vs. 9.75 Mg ha -1 ) and final plant density (5.58 vs. 4.95 plants m -2 ) were higher for southern than northern ecotypes. The southern-lowland combination exhibited the best yield and persistence over the study region, and genotypes within this group exhibited variability in yield among sites. Therefore, development of switchgrass cultivars for biomass production in the southern USA should focus on the southern-lowland genotypes.

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Biomass Yield and Stand Characteristics of Switchgrass in South Central U.S. Environments

Characteristics, chemical composition and utilisation of Albizia julibrissin seed oil

Switchgrass (Panicum virgatum L.) is a candidate feedstock in bioenergy, and plant breeding and molecular genetic strategies are being used to improve germplasm. In order to assess these subsequent modifications, baseline biomass compositional data are needed in a relevant variety of environments. In this study, switchgrass cv. Alamo was grown in the field, greenhouse, and growth chamber and harvested into individual leaf and stem tissue components. These components were analyzed with pyrolysis vapor analysis using molecular beam mass spectrometry, Fourier transform infrared, and standard wet chemistry methods to characterize and compare the composition among the different growth environments. The details of lignin content, S/G ratios, and degree of cross-linked lignin are discussed. Multivariate approaches such as projection to latent structures regression found a very strong correlation between the lignin content obtained by standard wet chemistry methods and the two high throughput techniques employed to rapidly assess lignin in potential switchgrass candidates. The models were tested on unknown samples and verified by wet chemistry. The similar lignin content found by the two methods shows that both approaches are capable of determining lignin content in biomass in a matter of minutes.

P.A. Rose

Papers

Biomass production from selected herbaceous species in the southeastern USA

Mimosa could be a new forage legume.