Current knowledge of yield potential and best agronomic management practices for perennial bioenergy grasses is primarily derived from small‐scale and short‐term studies, yet these studies inform policy at the national scale. In an effort to learn more about how bioenergy grasses perform across multiple locations and years, the U.S. Department of Energy (US DOE)/Sun Grant Initiative Regional Feedstock Partnership was initiated in 2008. The objectives of the Feedstock Partnership were to (1) provide a wide range of information for feedstock selection (species choice) and management practice options for a variety of regions and (2) develop national maps of potential feedstock yield for each of the herbaceous species evaluated. The Feedstock Partnership expands our previous understanding of the bioenergy potential of switchgrass, Miscanthus, sorghum, energycane, and prairie mixtures on Conservation Reserve Program land by conducting long‐term, replicated trials of each species at diverse environments in the U.S. Trials were initiated between 2008 and 2010 and completed between 2012 and 2015 depending on species. Field‐scale plots were utilized for switchgrass and Conservation Reserve Program trials to use traditional agricultural machinery. This is important as we know that the smaller scale studies often overestimated yield potential of some of these species. Insufficient vegetative propagules of energycane and Miscanthus prohibited farm‐scale trials of these species. The Feedstock Partnership studies also confirmed that environmental differences across years and across sites had a large impact on biomass production. Nitrogen application had variable effects across feedstocks, but some nitrogen fertilizer generally had a positive effect. National yield potential maps were developed using PRISM‐ELM for each species in the Feedstock Partnership. This manuscript, with the accompanying supplemental data, will be useful in making decisions about feedstock selection as well as agronomic practices across a wide region of the country.

The Regional Feedstock Partnership is a collaborative effort between the Sun Grant Initiative (through Land Grant Universities), the US Department of Energy, and the US Department of Agriculture. One segment of this partnership is the field-scale evaluation of switchgrass (Panicum virgatum L.) in diverse sites across the USA. Switchgrass was planted (11.2 kg PLS ha⁻¹) in replicated plots in New York, Oklahoma, South Dakota, and Virginia in 2008 and in Iowa in 2009. Adapted switchgrass cultivars were selected for each location and baseline soil samples collected before planting. Nitrogen fertilizer (0, 56, and 112 kg N ha⁻¹) was applied each spring beginning the year after planting, and switchgrass was harvested once annually after senescence. Establishment, management, and harvest operations were completed using field-scale equipment. Switchgrass production ranged from 2 to 11.5 Mg ha⁻¹ across locations and years. Yields were lowest the first year after establishment. Switchgrass responded positively to N in 6 of 19 location/year combinations and there was one location/year combination (NY in Year 2) where a significant negative response was noted. Initial soil N levels were lowest in SD and VA (significant N response) and highest at the other three locations (no N response). Although N rate affected some measures of biomass quality (N and hemicellulose), location and year had greater overall effects on all quality parameters evaluated. These results demonstrate the importance of local field-scale research and of proper N management in order to reduce unnecessary expense and potential environmental impacts of switchgrass grown for bioenergy.

A principle attribute of perennial grasses for biomass energy is the potential for high yields on marginal lands. Objectives of this study were to compare biomass and seed production of intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth and D.R. Dewey), big bluestem (Andropogon gerardii Vitman), and switchgrass (Panicum virgatum L.) as affected by harvest timing and manure application on two topographic positions (footslope and backslope). Footslope is the hillslope position that forms the inclined surface at the base of a slope and backslope forms the steepest, middle position of the hillslope. Grasses were harvested for biomass at anthesis (summer), after a killing frost (autumn), or the following spring after overwintering in the field. Seed was harvested at maturity during 2003 and 2004. Two rates of beef cattle (Bos taurus L.) manure (target rates of 0 and 150 kg total‐N ha⁻¹) were surface applied annually. Maximum annual biomass yield ranged from 4.4 to 5.2, 2.7 to 4.2, and 3.7 to 5.6 Mg ha⁻¹ for intermediate wheatgrass, big bluestem, and switchgrass, respectively. Biomass yields were not different between fall and spring harvest treatments. Biomass yields of big bluestem and switchgrass at the backslope position were 86% and 96% of biomass yields at the footslope position with normal precipitation, respectively. Manure application increased biomass yield approximately 30% during the second year on both topographic positions. The highest seed yield was obtained from intermediate wheatgrass, followed by switchgrass and big bluestem. Utilizing these management practices in our environment, it appears that switchgrass and big bluestem could be allowed to overwinter in the field without suffering appreciable loss of biomass.