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Biofuels and bio-based products can be produced from a wide variety of herbaceous feedstocks. To supply enough biomass to meet the needs of a new bio-based economy, a suite of dedicated biomass species must be developed to accommodate a range of growing environments throughout the USA. Researchers from the United States Department of Agriculture’s Agricultural Research Service (USDA-ARS) and collaborators associated with the USDA Regional Biomass Research Centers have made major progress in understanding the genetics of switchgrass, sorghum, and other grass species and have begun to use this knowledge to develop new cultivars with high yields and appropriate traits for efficient conversion to bio-based products. Plant geneticists and breeders have discovered genes that reduce recalcitrance for biochemical conversion to ethanol and drop-in fuels. Progress has also been made in finding genes that improve production under biotic and abiotic stress from diseases, pests, and climatic variations.

Leafy spurge (Euphorbia esula L.) reduces northern Great Plains rangeland carrying capacity. Treatment strategies were evaluated that suppressed leafy spurge and facilitated establishment of mixtures of native grasses and legumes on range sites near Mason City and Tilden, Nebr. Glyphosate at 1,600 g a.i. (active ingredient) ha-1 was applied with or without imazapic at 140 or 210 g a.i. ha-1 in October 1995. In April 1996, standing crop was burned or mowed. Mixtures of native grasses [big bluestem (Andropogon gerardii Vitman), indiangrass (Sorghastrum nutans (L.) Nash), switchgrass (Panicum virgatum L.), little bluestem (Schizachyrium scoparium (Michx.) Nash), and sideoats grama (Bouteloua curtiplendula (Michx.) Torr.)] were then planted with or without native legumes [leadplant (Amorpha canescens (Nutt.) Pursh), Illinois bundleflower (Desmanthus illinoensis (Michx.) MacM.), and purple prairieclover (Petalostemum purpureum (Vent.) Rybd.)] at 440 pls m-2 into a non-tilled seedbed. Imazapic was applied at 70 g a.i. ha-1 in June 1996 to half the plots that had been treated with imazapic in October 1995. Frequency, dry matter yield, and leafy spurge density were measured 14 to 16 months after planting. Leafy spurge density and yield were least, and frequencies and yields of the planted grasses usually were greatest where imazapic had been applied with glyphosate in October 1995. Purple prairieclover was the only planted legume to persist 14 months after planting, and yields were greatest where imazapic was applied with glyphosate. Imazapic applied in June 1996 usually did not improve planted species yields or leafy spurge control. Total vegetation yields were greater where imazapic was applied with glyphosate at both sites and where native species were seeded at Mason City. Vegetation suppression with fallapplied herbicides and removal of standing crop enabled successful establishment of desirable species, increased forage yields, and suppressed leafy spurge.

Tallgrass prairies provide an important source of hay and summer forage in eastern Nebraska. A study was conducted in 1989 and 1990 on 2 late seral tallgrass prairies near Lincoln and Virginia, Nebraska to determine if production of selected components of tallgrass prairie communities could be altered by burning (not burned, or burned in either early, mid-, or late spring) and applying fertilizer (0 and 67-23 kg N-P ha-1) and atrazine [6- chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] (0 and 2.2 kg a.i. ha-1). Vegetation was harvested the year treatments were applied at about 30-day intervals starting in June and ending in August. Maximum big bluestem(Andropogon gerardii var. gerardii Vitman) accumulated standing crop (ASC) on unburned areas and areas burned in mid-spring occurred later in 1990 than in 1989. Burning in late spring 1989 maintained big bluestem ASC above 1,100 kg ha-1 through July, whereas big bluestem ASC declined below 840 kg ha-1 in July on areas where other burn treatments were applied. In 1990, big bluestem ASC exceeded 1,570 kg ha-1 in June on areas burned in early and midspring and exceeded 1,500 kg ha-1 in July on areas that were not burned or burned in mid- or late spring. From July to August 1990 big bluestem ASC declined below 730 kg ha-1 for all treatments except the late spring burn treatment where ASC was 1,340 kg ha-1. Burning in late spring reduced prairie dropseed [Sporoboluhs eterolepis( A. Gray) A. Gray] and tall dropseed [S. asper (Michx.) Kunth.] ASC by at least 67% in June 1990 compared to areas burned in early and mid-spring. Cool-season grass ASC at Virginia declined 86% in June when burned in late spring compared to areas that were not burned. Fertilization increased big bluestem ASC by about 23 and 29% in June and July. Vegetation response to atrazine was variable. Atrazine had a negligible effect on big bluestem ASC. Burning late seral tallgrass prairie in late spring increased big bluestem ASC later in the gr

The productivity and native species diversity of Great Plains grasslands have been substantially reduced by past management that facilitated the establishment of invasive exotic weeds and displacement of native species. Management strategies are needed to rapidly restore the productive capacity and biological diversity of these degraded grasslands. Critically important phases of the grassland restoration process are the reintroduction and establishment of native species. Weed interference is the primary constraint to successful establishment of native plants. The goal of our research is to develop strategies that use multiple technologies, including herbicides, to expedite grassland revegetation with native grasses and forbs. Imidazolinon eherbicides( AC 263,333, imazapyr, and imazethapyr) were used successfully to improve establishment of native perennial grasses (big bluestem, switchgrass, little bluestem) and selected forbs (blackeyed-susan, purple prairieclover, Illinois bundleflower, trailing crownvetch, and upright prairie coneflower) on cropland and as components of a strategy to revegetate leafy spurge-infested rangeland with native tallgrasses. Imazethapyr at 70 or 110 g ai/ha applied at planting resulted in stands of big bluestem and little bluestem that were similar or superior to stands established where atrazine was applied. Seedling grasses were susceptible to imazapyr at two of three study sites. Imazapyr at 560 g ai/ha plus sulfometuron at 100 g ai/ha applied in fall was the optimum treatment for suppression of leafy spurge and exotic cool-season grasses and establishment of big bluestem and switchgrass on degraded rangeland sites. Establishment of selected forbs was improved by PRE treatment with AC 263,222 or imazethapyr at 70 g ai/ha. This research provides evidence that the imidazolinone herbicides can be important components of integrated weed management strategies designed to reverse deterioration of grasslands by reestablishing native species

Tallgrass prairies are an important forage resource in the eastern Central Great Plains. The effect of spring burning, fertilization, and atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine- 2,4-diamine] on standing crop of selected herbaceous species and categories of vegetation was determined in 6 tallgrass prairie environments located near Lincoln and Virginia, Neb., from 1987 through 1989 and 1 site near Bloomfield, Neb., in 1987. The grasslands were in good to excellent condition at the time these studies were conducted. Portions of each site were burned in mid-to late spring, atrazine was applied at a rate of 2.2 kg a.i. ha-1 in late April to early May, and fertilizer was applied in mid-May. Despite below-normal precipitation at 6 of the 7 sites, burning combined with fertilization improved warm-season grass standing crop by 50 to 127% in 5 of the 7 grassland environments studied. This reflected the positive response of the dominant warm-season grasses, big bluestem (Andropogon gerardii Vitman var. gerardii Vitman) and indiangrass [Sorghastrum nutans (L.) Nash], to burning or fertilization. Atrazine increased warm-season grass standing crop at only the site near Bloomfield. Kentucky bluegrass (Poa pratensis L.) and annual bromes (Bromus spp.) were more susceptible to atrazine than smooth brome (Bromus inermis Leyss.). Forb standing crop was significantly reduced by atrazine alone or by burning followed by atrazine application in 4 of the 7 prairie environments. Burning combined with fertilizer application improved warm-season grass standing crop in good to excellent condition grasslands and obviated the need to use atrazine.