Conservation Reserve Program (CRP) land on which perennial warm‐season grasses are grown could be a resource for bioenergy feedstock production and C sequestration. A 4‐yr field experiment was conducted to determine the response of switchgrass (Panicum virgatum L.) and soil C sequestration to N fertility and harvest frequency on switchgrass‐dominated CRP land in eastern South Dakota. Soil at the site is an Egan silty clay loam. Three N rates (0, 112, and 224 kg ha−1) were applied as NH4NO3 (NH4NO3–N) and cattle (Bos taurus L.) manure (manure‐N). Switchgrass was harvested at anthesis every year (EY) or alternate years (AY) from 2001 to 2004. Soil samples were collected before starting the experiment (fall 2000) and after 4 yr (fall 2004) to determine C sequestration. Averaged across N rate, the proportion of switchgrass was higher with manure‐N (64.7%) than NH4NO3‐N (46.8%). Total (switchgrass plus other herbaceous material) biomass production tended to be higher when harvested EY (average 5.0 Mg ha−1 yr−1) compared with AY (average 4.0 Mg ha−1 yr−1). However, by 2004, the proportion of switchgrass was 75% higher in plots harvested AY compared with those harvested EY. The concentration of structural components was greater in biomass harvested AY, whereas total N and ash tended to be lower. Total‐N and ash concentrations in biomass were higher with NH4NO3‐N than manure‐N. Soil C was sequestered at a rate of 2.4 ± 0.9 and 4.0 ± 1.0 Mg C ha−1 yr−1 at the 0‐ to 90‐cm depth with NH4NO3–N and manure‐N, respectively. There were no changes in soil organic C without N fertilization. Manure could be used as an alternate N source for switchgrass biomass production on CRP land with an added benefit of increased C sequestration.

Prairie cordgrass (Spartina pectinata Link.) is tall, rhizomatous, and native to marshes, drainage ways, and moist prairies in North America. Our objectives were to determine genetic variation among cordgrass populations for biomass production, to describe the distribution of biomass among phytomers and between leaf and stem components of cordgrass, to compare biomass production and composition of cordgrass to switchgrass (Panicum virgatum L.), and to determine heritability for biomass production in switchgrass. Seven populations of cordgrass and ‘Cave‐In‐Rock’, ‘Summer’, and ‘Sunburst’ switchgrass were harvested in October in 2001 through 2004. Mean biomass production across years ranged from 5.1 to 7. 9 Mg ha−1 among cordgrass populations. Yields of cordgrass (6.0 Mg ha−1) were similar to Cave‐In‐Rock (6.8 Mg ha−1) for the first two years. However production in the fourth year was greater for cordgrass (6.8 Mg ha−1) than Cave‐In‐Rock (2.0 Mg ha−1). Two cordgrass populations produced more biomass (9.3 Mg ha−1) than Summer and Sunburst (4.8 Mg ha−1) in the fourth year. Leaf comprised 70% of the biomass of cordgrass, and differences occurred among phytomers for leaf and internode traits. Cellulose and hemicellulose concentrations were similar for cordgrass and switchgrass, but cordgrass had higher levels of total N and ash. Narrow‐sense heritability estimates for biomass production in Summer and Sunburst switchgrass were 0.6. Biomass production of native warm‐season grasses intended for biofuel purposes in the northern Great Plains may be enhanced by selecting among populations of cordgrass and among families within cultivars of switchgrass.