Management of warm-season grass mixtures for biomass production in South Dakota USA

Climate vs Energy Security: Quantifying the Trade-offs of BECCS Deployment and Overcoming Opportunity Costs on Set-Aside Land

Bioenergy with carbon capture and storage (BECCS) sits at the nexus of the climate and energy security. We evaluated trade-offs between scenarios that support climate stabilization (negative emissions and net climate benefit) or energy security (ethanol production). Our spatially explicit model indicates that the foregone climate benefit from abandoned cropland (opportunity cost) increased carbon emissions per unit of energy produced by 14-36%, making geologic carbon capture and storage necessary to achieve negative emissions from any given energy crop. The toll of opportunity costs on the climate benefit of BECCS from set-aside land was offset through the spatial allocation of crops based on their individual biophysical constraints. Dedicated energy crops consistently outperformed mixed grasslands. We estimate that BECCS allocation to land enrolled in the Conservation Reserve Program (CRP) could capture up to 9 Tg C year-1 from the atmosphere, deliver up to 16 Tg CE year-1 in emissions savings, and meet up to 10% of the US energy statutory targets, but contributions varied substantially as the priority shifted from climate stabilization to energy provision. Our results indicate a significant potential to integrate energy security targets into sustainable pathways to climate stabilization but underpin the trade-offs of divergent policy-driven agendas.

Annual changes in biomass amount and feeding potential of shrubby rangelands in maquis formation

Background

This study evaluated the extent to which the endemic herbaceous and woody species of shrubby rangelands met the roughage needs of grazing animals throughout the year.

Methods

The biomass, botanical composition, and quality of hay were investigated in the shrubby rangelands in Paşaköy of the Ayvacık districts in Çanakkale over the course of a year. Plant samples were taken from the herbaceous species monthly and from the grazing parts of the shrubs in May and November.

Results

The total amount of biomass (hay + shrub) in the rangeland was found to be 30.448 kg/ha. Shrubs made up 18.78% of the rangeland, while the annual species comprised 54.96%, and perennial herbs covered 26.26% of the total biomass. Crude protein (CP) ratios of herbaceous species decreased continuously from March (13.58%) to September (6.73%), and then increased. A similar change was also seen in pure ash (PA) ratios. The CP ratios in the shrub species were high in spring and decreased in autumn and there was an irregular variation in PA rates. Oak had the highest PA ratio during the spring, while thuja had the highest ratio in autumn, and Juniperus oxycedrus during the winter months. In herbaceous species, cell wall components (NDF, ADF, and ADL) reached their highest levels in summer and decreased in spring and winter. However, in shrubs, these components varied according to the species and were generally lowest in spring and then increased in autumn and winter. Here, it was determined that year-round grazing is a suitable grazing system in the shrubby rangelands of the Mediterranean zone, and animals are able to find fresh forage in the rangelands due to the presence of shrubs. However, since the contribution of shrubs to the total forage production is low, additional roughage should be provided, except in the spring when the production and quality of hay increase. These practices may contribute to better livestock management.

Xylitol Production by Candida Species from Hydrolysates of Agricultural Residues and Grasses

Xylitol is an industrially important chemical due to its commercial applications. The use of xylitol as a sweetener as well as its utilization in biomedical applications has made it a high value specialty chemical. Although several species of yeast synthesize xylitol, this review focusses on the species of the genus Candida. The importance of the enzyme xylitol reductase present in Candida species as it relates to their ability to synthesize xylitol was examined. Another focus of this work was to review prior studies examining the ability of the Candida species to synthesize xylitol effectively from hydrolysates of agricultural residues and grasses. An advantage of utilizing such a hydrolysate as a substrate for yeast xylitol production would be decreasing the overall cost of synthesizing xylitol. The intent of this review was to learn if such hydrolysates could substitute for xylose as a substrate for the yeast when producing xylitol. In addition, a comparison of xylitol production by Candida species should indicate which hydrolysate of agricultural residues and grasses would be the best substrate for xylitol production. From studies analyzing previous hydrolysates of agricultural residues and grasses, it was concluded that a hydrolysate of sugarcane bagasse supported the highest level of xylitol by Candida species, although corncob hydrolysates also supported significant yeast xylitol production. It was also concluded that fewer studies examined yeast xylitol production on hydrolysates of grasses and that further research on grasses may provide hydrolysates with a higher xylose content, which could support greater yeast xylitol production.

Arsenic Accumulation in Hydroponically Grown Schizachyrium scoparium (Little Bluestem) Amended with Root-Colonizing Endophytes

We integrated microscopy, spectroscopy, culturing and molecular biology, and aqueous chemistry techniques to evaluate arsenic (As) accumulation in hydroponically grown Schizachyrium scoparium inoculated with endophytic fungi. Schizachyrium scoparium grows in historically contaminated sediment in the Cheyenne River Watershed and was used for laboratory experiments with As(V) ranging from 0 to 2.5 mg L^-1 at circumneutral pH. Arsenic accumulation in regional plants has been a community concern for several decades, yet mechanisms affecting As accumulation in plants associated with endophytic fungi remain poorly understood. Colonization of roots by endophytic fungi supported better external and vascular cellular structure, increased biomass production, increased root lengths and increased P uptake, compared to noninoculated plants (p value <0.05). After exposure to As(V), an 80% decrease of As was detected in solution and accumulated mainly in the roots (0.82-13.44 mg kg^-1) of noninoculated plants. Endophytic fungi mediated intracellular uptake into root cells and translocation of As. Electron microprobe X-ray mapping analyses detected Ca-P and Mg-P minerals with As on the root surface of exposed plants, suggesting that these minerals could lead to As adsorption on the root surface through surface complexation or coprecipitation. Our findings provide new insights regarding biological and physical-chemical processes affecting As accumulation in plants for risk assessment applications and bioremediation strategies.

Effect of pH on xylitol production by Candida species from a prairie cordgrass hydrolysate

Using hydrolysates of the North American prairie grass prairie cordgrass buffered at pH 4.5, 5.0, 5.5 or 6.0, xylitol production, xylitol yield, cell biomass production and productivity were investigated for three strains of yeast Candida. Of the three strains, the highest xylitol concentration of 20.19 g xylitol (g xylose consumed)-1 and yield of 0.89 g xylitol (g xylose consumed)-1 were produced by Candida mogi ATCC 18364 when grown for 120 h at 30° C on the pH 5.5-buffered hydrolysate-containing medium. The highest biomass level being 7.7 g cells (kg biomass)-1 was observed to be synthesized by Candida guilliermondii ATCC 201935 after 120 h of growth at 30° C on a pH 5.5-buffered hydrolysate-containing medium. The highest xylitol specific productivity of 0.73 g xylitol (g cells h)-1 was determined for C. guilliermondii ATCC 20216 after 120 h of growth at 30°C on a pH 5.0-buffered hydrolysate-containing medium. Xylitol production and yield by the three Candida strains was higher on prairie cordgrass than what was previously observed for the same strains after 120 h at 30° C when another North American prairie grass big bluestem served as the plant biomass hydrolysate indicating that prairie cordgrass may be a superior plant biomass substrate.

Cultivar and phosphorus effects on switchgrass yield and rhizosphere microbial diversity

Switchgrass (Panicum virgatum L.) is a native perennial grass identified as a promising biofuel crop for production on marginal agricultural lands. As such, research into switchgrass fertility and the switchgrass rhizosphere microbiome has been ongoing in an effort to increase production sustainability. We examined the effects of cultivar and phosphorus (P) fertilization on biomass yield, P removal, and rhizosphere bacterial and fungal community structure in three switchgrass cultivars: Sunburst, Shawnee, and Liberty. The Liberty cv. is the first lowland-type bioenergy switchgrass adapted to USDA hardiness zones 4, 5, and 6. On a medium soil test P clay loam soil, biomass yield response to applied P was linear, increasing 135 kg ha^-1 for every kilogram of P applied prior to establishment. Average post-frost biomass yield was 9.6 Mg ha^-1 year^-1 when unfertilized, and maximum biomass yield was 10.3 Mg ha^-1 year^-1 when fertilized at 58.6 kg ha^-1 P, suggesting that P application on medium soil test P soils is beneficial for switchgrass establishment and early growth. Switchgrass cv. Shawnee was more productive than cvs. Liberty or Sunburst (11.3, 10.2, and 8.6 Mg ha^-1 year^-1, respectively). Both bacterial and fungal communities were significantly shaped by cultivar. These shifts, while inconsistent between year and cultivar, may reflect a selection of the microbial community from that present in soil to maximize total nutrient uptake, regardless of additional P amendments. Phosphorus fertilization did not affect microbial community structure. Results of this study suggest that the cultivar-associated selection of particular microbial taxa may have implications for increased productivity.

Alternative scenarios of bioenergy crop production in an agricultural landscape and implications for bird communities

Increased demand and government mandates for bioenergy crops in the United States could require a large allocation of agricultural land to bioenergy feedstock production and substantially alter current landscape patterns. Incorporating bioenergy landscape design into land-use decision making could help maximize benefits and minimize trade-offs among alternative land uses. We developed spatially explicit landscape scenarios of increased bioenergy crop production in an 80-km radius agricultural landscape centered on a potential biomass-processing energy facility and evaluated the consequences of each scenario for bird communities. Our scenarios included conversion of existing annual row crops to perennial bioenergy grasslands and conversion of existing grasslands to annual bioenergy row crops. The scenarios explored combinations of four biomass crop types (three potential grassland crops along a gradient of plant diversity and one annual row crop [corn]), three land conversion percentages to bioenergy crops (10%, 20%, or 30% of row crops or grasslands), and three spatial configurations of biomass crop fields (random, clustered near similar field types, or centered on the processing plant), yielding 36 scenarios. For each scenario, we predicted the impact on four bird community metrics: species richness, total bird density, species of greatest conservation need (SGCN) density, and SGCN hotspots (SGCN birds/ha ≥ 2). Bird community metrics consistently increased with conversion of row crops to bioenergy grasslands and consistently decreased with conversion of grasslands to bioenergy row crops. Spatial arrangement of bioenergy fields had strong effects on the bird community and in some cases was more influential than the amount converted to bioenergy crops. Clustering grasslands had a stronger positive influence on the bird community than locating grasslands near the central plant or at random. Expansion of bioenergy grasslands onto marginal agricultural lands will likely benefit grassland bird populations, and bioenergy landscapes could be designed to maximize biodiversity benefits while meeting targets for biomass production.

Bird communities and biomass yields in potential bioenergy grasslands

Demand for bioenergy is increasing, but the ecological consequences of bioenergy crop production on working lands remain unresolved. Corn is currently a dominant bioenergy crop, but perennial grasslands could produce renewable bioenergy resources and enhance biodiversity. Grassland bird populations have declined in recent decades and may particularly benefit from perennial grasslands grown for bioenergy. We asked how breeding bird community assemblages, vegetation characteristics, and biomass yields varied among three types of potential bioenergy grassland fields (grass monocultures, grass-dominated fields, and forb-dominated fields), and assessed tradeoffs between grassland biomass production and bird habitat. We also compared the bird communities in grassland fields to nearby cornfields. Cornfields had few birds compared to perennial grassland fields. Ten bird Species of Greatest Conservation Need (SGCN) were observed in perennial grassland fields. Bird species richness and total bird density increased with forb cover and were greater in forb-dominated fields than grass monocultures. SGCN density declined with increasing vertical vegetation density, indicating that tall, dense grassland fields managed for maximum biomass yield would be of lesser value to imperiled grassland bird species. The proportion of grassland habitat within 1 km of study sites was positively associated with bird species richness and the density of total birds and SGCNs, suggesting that grassland bioenergy fields may be more beneficial for grassland birds if they are established near other grassland parcels. Predicted total bird density peaked below maximum biomass yields and predicted SGCN density was negatively related to biomass yields. Our results indicate that perennial grassland fields could produce bioenergy feedstocks while providing bird habitat. Bioenergy grasslands promote agricultural multifunctionality and conservation of biodiversity in working landscapes.

Nutritive Value Response of Native Warm-Season Forage Grasses to Harvest Intervals and Durations in Mixed Stands

Interest in management of native warm-season grasses for multiple uses is growing in southeastern USA. Forage quality response of early-succession mixed stands of big bluestem (BB, Andropogon gerardii), indiangrass (IG, Sorghastrum nutans), and little bluestem (SG, Schizachyrium scoparium) to harvest intervals (30-, 40-, 60-, 90 or 120-d) and durations (one or two years) were assessed in crop-field buffers. Over three years, phased harvestings were initiated in May, on sets of randomized plots, ≥90 cm apart, in five replications (blocks) to produce one-, two-, and three-year-old stands, by the third year. Whole-plot regrowths were machine-harvested after collecting species (IG and LB) sample tillers for leafiness estimates. Species-specific leaf area (SLA) and leaf-to-stem ratio (LSR) were greater for early-season harvests and shorter intervals. In a similar pattern, whole-plot crude protein concentrations were greatest for the 30-d (74 g·kg⁻¹ DM) and the least (40 g·kg⁻¹ DM) for the 120-d interval. Corresponding neutral detergent fiber (NDF) values were the lowest (620 g·kg⁻¹ DM) and highest (710 g·kg⁻¹ DM), respectively. In vitro dry matter and NDF digestibility were greater for early-season harvests at shorter intervals (63 and 720 g·kg⁻¹ DM). With strategic harvesting, similar stands may produce quality hay for beef cattle weight gain.

Energy potential of biomass from conservation grasslands in Minnesota, USA

Perennial biomass from grasslands managed for conservation of soil and biodiversity can be harvested for bioenergy. Until now, the quantity and quality of harvestable biomass from conservation grasslands in Minnesota, USA, was not known, and the factors that affect bioenergy potential from these systems have not been identified. We measured biomass yield, theoretical ethanol conversion efficiency, and plant tissue nitrogen (N) as metrics of bioenergy potential from mixed-species conservation grasslands harvested with commercial-scale equipment. With three years of data, we used mixed-effects models to determine factors that influence bioenergy potential. Sixty conservation grassland plots, each about 8 ha in size, were distributed among three locations in Minnesota. Harvest treatments were applied annually in autumn as a completely randomized block design. Biomass yield ranged from 0.5 to 5.7 Mg ha⁻¹. May precipitation increased biomass yield while precipitation in all other growing season months showed no affect. Averaged across all locations and years, theoretical ethanol conversion efficiency was 450 l Mg⁻¹ and the concentration of plant N was 7.1 g kg⁻¹, both similar to dedicated herbaceous bioenergy crops such as switchgrass. Biomass yield did not decline in the second or third year of harvest. Across years, biomass yields fluctuated 23% around the average. Surprisingly, forb cover was a better predictor of biomass yield than warm-season grass with a positive correlation with biomass yield in the south and a negative correlation at other locations. Variation in land ethanol yield was almost exclusively due to variation in biomass yield rather than biomass quality; therefore, efforts to increase biomass yield might be more economical than altering biomass composition when managing conservation grasslands for ethanol production. Our measurements of bioenergy potential, and the factors that control it, can serve as parameters for assessing the economic viability of harvesting conservation grasslands for bioenergy.

Bioenergy from permanent grassland--a review: 2. Combustion

The aim of this review is to summarize current knowledge on suitability and sustainability of grassland biomass for combustion. In the first section grassland management for solid biofuel as well as information on harvest, postharvest and firing technology are described. An extensive grassland management system with one late cut and low level of fertilization is favored for grass as a solid biofuel. The grass harvest usually involves drying in the field and clearing with conventional farm machinery. Pelleting or briquetting improves the biofuel quality. Grass combustion is possible as stand-alone biomass-firing or co-firing with other fuels. Firing herbaceous biomass requires various specific adaptations of the different combustion technologies. In the second section economic and environmental aspects are discussed. Costs for biomass supply mainly depend on yields and harvesting technologies, while combustion costs are influenced by the size and technical design of the plant. Market prices for grass and possible subsidies for land use are crucial for profitability. Regarding biogeochemical cycles a specific feature of combustion is the fact that none of the biomass carbon and nitrogen removed at harvest is available for return to the grassland. These exports can be compensated for by fixation from the air given legumes in the vegetation and sufficient biomass production. Greenhouse gas emissions can be considerably reduced by grass combustion. Solid biofuel production has a potential for predominantly positive impacts on biodiversity due to the extensive grassland management.

Long-term productivity of lowland and upland switchgrass cytotypes as affected by cutting frequency

A considerable number of studies has been conducted on switchgrass (Panicum virgatum L.) as a bioresource for energy over the last few years. Nonetheless, some important issues concerning the agro-technique are still open. This research examines the long-term total dry matter yield (TDM) and ash content of two lowland (L) and two upland (U) switchgrass cytotypes, as affected by one or two-cut system, under southern EU climatic conditions (44 degrees 33' N). Overall, L produced higher TDM than U (on average 14.9 and 11.7 Mg ha(-1), respectively); two-cut system allowed to produce higher biomass yields (especially in U) than single harvest during the two first years, but it also drastically reduced plant vigour and productivity of all cytotypes in the following two years. Moreover, under two-cut system almost total seasonal biomass derived from the early harvest, while the second cut slightly contributed to the total seasonal biomass, nor it appeared to offset the additional harvest costs. Biomass quality was also significantly affected by cutting frequency, with two-cut system leading to a considerably higher ash content of biomass. Therefore, it is perceived that two-cut system is not worthwhile with U and L cytotypes as bioresource for energy production under southern EU conditions.