Switchgrass Production Research Articles

Effect of cultivation technology on switchgrass (Panicum virgatum L.) productivity in marginal lands in Ukraine

Growing plants for biofuel production on marginal lands is of major importance in many developing countries. As a biomass source, switchgrass (<em>Panicum virgatum</em> L.) is a most adaptable plastic crop, forming extensive ground cover and vegetative biomass, providing a very high productivity over a short period of time. This study investigated the effects of cultivation (type of growing conditions and N fertilization rates) on biomass yields and changes in the structure of the switchgrass phytocenosis in different types of cropping systems. The biomass yields in stripe and mixed crops were higher than in single crops in the third year of cultivation. Switchgrass plants in intercrops were characterized by a greater height and number of shoots per unit area compared to mixed crops and monocultures. Biomass yields increased with each year of this research. The maximum biomass yields were attained with 30 kg ha<sup>−1</sup> of N fertilization and the minimum yields where there was no fertilization.

Plant Diversity and Fertilizer Management Shape the Belowground Microbiome of Native Grass Bioenergy Feedstocks.

Plants may actively cultivate microorganisms in their roots and rhizosphere that enhance their nutrition. To develop cropping strategies that substitute mineral fertilizers for beneficial root symbioses, we must first understand how microbial communities associated with plant roots differ among plant taxa and how they respond to fertilization. Arbuscular mycorrhizal (AM) fungi and rhizobacteria are of particular interest because they enhance nutrient availability to plants and perform a suite of nutrient cycling functions. The purpose of this experiment is to examine the root and soil microbiome in a long-term switchgrass (Panicum virgatum) biofuel feedstock experiment and determine how AM fungi and rhizobacteria respond to plant diversity and soil fertility. We hypothesize that intra- and interspecific plant diversity, nitrogen fertilization (+N), and their interaction will influence the biomass and community composition of AM fungi and rhizobacteria. We further hypothesize that +N will reduce the abundance of nitrogenase-encoding nifH genes on the rhizoplane. Roots and soils were sampled from three switchgrass cultivars (Cave-in-Rock, Kanlow, Southlow) grown in monoculture, intraspecific mixture, and interspecific planting mixtures with either Andropogon gerardii or diverse native tallgrass prairie species. Molecular sequencing was performed on root and soil samples, fatty acid extractions were assessed to determine microbial biomass, and quantitative polymerase chain reaction (qPCR) was performed on nifH genes from the rhizoplane. Sequence data determined core AM fungal and bacterial microbiomes and indicator taxa for plant diversity and +N treatments. We found that plant diversity and +N influenced AM fungal biomass and community structure. Across all plant diversity treatments, +N reduced the biomass of AM fungi and nifH gene abundance by more than 40%. The AM fungal genus Scutellospora was an indicator for +N, with relative abundance significantly greater under +N and in monoculture treatments. Community composition of rhizobacteria was influenced by plant diversity but not by +N. Verrucomicrobia and Proteobacteria were the dominant bacterial phyla in both roots and soils. Our findings provide evidence that soil fertility and plant diversity structure the root and soil microbiome. Optimization of soil communities for switchgrass production must take into account differences among cultivars and their unique responses to shifts in soil fertility.

Dynamics and Uncertainty in Land Use Conversion for Perennial Energy Crop Production: Exploring Effects of Payments for Ecosystem Services Policies

Perennial energy crops like switchgrass that are used for biofuel production have the potential to generate various water quality benefits such as reduced nitrogen runoff. Yet the current expected returns to switchgrass are not profitable enough for these crops to be widely adopted by U.S. farmers due to relatively unstable yields, volatile revenues, and high costs of crop establishment. This study uses a dynamic economic model to investigate the uncertainties in the yields and costs of switchgrass production, in comparison with those of corn-soybeans in the Chesapeake Bay Watershed in Pennsylvania. Results indicate that farmers would be willing to convert corn-soybeans to switchgrass land use with the provision of payments for ecosystem services (PES). A targeted PES policy based on the environmental effectiveness of the crop land is found to be slightly more effective in providing nitrogen reductions than a uniform PES policy with cost savings of 8–19%. Moreover, switchgrass has the potential of providing energy supply while reducing greenhouse gases emissions.

Biomass Production and Soil Carbon Analysis of Switchgrass under Rainfed or Minimal Irrigation in a Semiarid Environment

Core Ideas In this study, switchgrass grew well on marginally saline soil with limited irrigation.The southern‐origin cultivars had greater biomass yield than the northern cultivars.Irrigation increased above and below ground biomass, but not soil C and N content.Switchgrass had the potential to sequester C into the soil. Limited information is available on switchgrass (Panicum virgatum L.) productivity in semiarid environments. A field experiment was conducted in semiarid Colorado, with the objectives were to determine: 1) aboveground biomass production of six upland switchgrass cultivars, and 2) soil organic carbon content of two switchgrass cultivars grown on a marginally saline soil under rainfed and minimal irrigation conditions. The experiment was a split plot design with rainfed vs. minimal irrigation treatment as the main plot and six cultivars [three southern cultivars (Blackwell, Pathfinder, and Trailblazer) and three northern cultivars (Sunburst, Forestburg, and Dacotah)] as subplot with three replications. Aboveground biomass for the six cultivars ranged from 1.1 to 7.8 Mg ha−1yr−1 in the establishment year, and 3.2–9.3 and 3.3–11.7 Mg ha−1yr−1 under rainfed and minimally irrigated conditions, respectively, during the following three stand years. Minimal irrigation (mean annual irrigation water of 21 cm) increased biomass yield compared to the rainfed control. Southern‐origin cultivars produced more biomass than the northern lines under both rainfed and minimal irrigation. Four years after establishment, within the top 0.6 m of soil, irrigation increased root biomass, with averages of 9.9 and 5.2 Mg ha−1 yr−1 for irrigation and rainfed treatments, respectively. Soil organic carbon accumulated rapidly at 0–20 cm soil depth in Blackwell and Pathfinder plots, at the rates of 1.07–1.36 Mg C ha−1 yr−1. Switchgrass growth in the semiarid environment was improved with limited supplemental irrigation and had the potential to sequester C into soil.

An Economic Assessment of Nutrient Removal from Switchgrass Production

The on-site loss of nutrients due to biomass removal creates additional costs for ethanol production however this aspect has not been properly incorporated in economic analyses of biomass production and processing. This study investigates costs of on-site nutrient losses in switchgrass fields in Tennessee. The replacement cost methodology was applied to measure on-site cost of nutrient losses due to biomass removal and was based on the costs of replacing nutrients removed from the production site. The estimated costs for total on-site nutrient loss due to biomass removal show a substantial loss of nutrients in switchgrass fields. The loss of major nutrients from biomass removal represents the major part of on-site economic costs. A declining trend of nutrient costs per Mg of harvested biomass was observed with increasing in harvesting time. The internalization of on-site costs of nutrient losses is possible by adopting an appropriate harvest schedule for switchgrass.

Adopting bioenergy crops: Does farmers’ attitude toward loss matter?

AbstractWe apply prospect theory to examining farmers’ economic incentives to divert a share of their land to bioenergy crops (miscanthus and switchgrass in this study). Numerical simulation is conducted for 1,919 rain‐fed U.S. counties to identify the impact of loss aversion on bioenergy crop adoption, and how this impact is influenced by biomass price, discount rate, credit constraint status, and policy instruments. Results show that ignoring farmer's loss aversion causes overestimation of miscanthus production but underestimation of switchgrass production, particularly when farmers are credit constrained and have a high discount rate. We find that establishment cost subsidy induces more miscanthus production whereas subsidized energy crop insurance induces more switchgrass production. The efficacy of these two policy instruments, measured by biomass production increased by per dollar of government outlay, depends on the magnitude of farmers’ loss aversion and discount rate.

Effects of nitrogen rate and harvest time on biomass yield and nutrient cycling of switchgrass and soil nitrogen balance in a semiarid sandy wasteland

Increasing demand for renewable energy has stimulated energy crop cultivation on marginal lands with low production potential. This study investigates potential biomass yield of switchgrass (Panicum virgatum L., cv. Blackwell), plant nutrient (nitrogen, N; phosphorus, P; potassium, K) concentration and uptake, N-use efficiency (NUE) and apparent soil N balance in a semiarid rainfed sandy wasteland of Inner Mongolia, China. The aim of this study was to optimize N fertilizer rate and harvest time to produce quality biomass sustainably with minimal soil nutrient removal through harvested crop biomass. Five N rates (0, 60, 120, 180, 240 kg N ha−1) and two harvest times (late summer and early fall) in one-cut system were evaluated in 2015 and 2016. Nitrogen application of 60 kg N ha‒1 significantly increased aboveground plant (AGP) biomass yield by 14.3% vs. control only during early fall harvest in 2016, with no yield response at rates >60 kg N ha−1. AGP nutrient concentration and nutrient uptake increased by increasing N rate, except for P concentration, which decreased. Partial factor productivity (PFP) and agronomic NUE (ANUE) of applied N fertilizer decreased quadratically with N rates >60 kg N ha−1. Apparent soil N budget study revealed an N deficit (0–20 cm depth) in control while N surplus increased as N rate increased which likely boosted NO3- leaching. An early fall harvest exhibited 12.5% higher biomass yield and substantially reduced biomass N and K concentration and uptake relative to late summer harvest. These findings demonstrate that an N input not exceeding 60 kg N ha−1 would be sufficient to optimize biomass yields of Blackwell switchgrass and maintain the soil N balance on a semiarid rainfed sandy wasteland of Inner Mongolia when harvested in early fall. Therefore, N fertilization and harvest time practices should be considered simultaneously in switchgrass production systems for the continuous and sustainable biomass supply with increased feedstock quality and reduced crop fertilizer requirements.

Impacts of nitrogen fertilization rate and landscape position on select soil properties in switchgrass field at four sites in the USA

Switchgrass (Panicum virgatum L.) has been recognized as a potential bioenergy feedstock due to its high yield potential and benefits to the environment. However, little is known about the impacts of nitrogen fertilization and landscape position on soil properties in switchgrass fields at multiple locations in the USA. The objective of this study was to assess the impacts of application of nitrogen fertilization rate (N rate; zero, 0; medium, 56; and high, 112 kg ha−1) and landscape position (shoulder, backslope, and footslope) on soil pH, electrical conductivity (EC), soil organic carbon (SOC), total nitrogen (TN), nitrate-N (NO3−-N), and ammonium-N (NH4+-N). This experiment was established in 2008 at four sites in Oklahoma (OK), South Dakota (SD), New York (NY), and Virginia (VA). Data showed that the N rate significantly increased NO3−-N for the 0–5 and 5–15 cm depths at the SD, NY, and VA sites. Compared with the zero N rate, the high N rate averagely increased NO3−-N by 75.7% for the two depths and three sites. The SOC and TN increased with the increase in N rate at most of the depths. The landscape position significantly reduced soil pH and increased EC, SOC, TN, NO3−-N, and NH4+-N at the footslope compared with the shoulder and backslope positions in most depths at the SD site (no position data at the NY and VA sites). The pH generally increased and the SOC, TN, and NO3−-N reduced with the increase in soil depth. These findings indicate that switchgrass production has the potential to improve or maintain soils in the USA.

Soil hydrological properties as influenced by long‐term nitrogen application and landscape positions under switchgrass seeded to a marginal cropland

AbstractSwitchgrass (Panicum virgatum L.) has the potential to recover the soil hydrological properties of marginal lands. Nitrogen (N) and landscape position are the key factors in impacting these soil properties under switchgrass. The specific objective of this study was to investigate the responses of N rate (low, 0 kg N/ha and high, 112 kg N/ha) and landscape positions (shoulder and footslope) on near‐surface soil hydrological properties that included: infiltration rate (qs), saturated hydraulic conductivity (Ksat), bulk density (ρb), penetration resistance (SPR), water retention (SWR), pore‐size distribution (PSD), and carbon (C) and nitrogen (N) fractions under switchgrass production. Data showed that, in general, the N and landscape position significantly influenced soil hydrological properties. Higher N rate decreased ρb (1.23 and 1.36 g/cm3 at 0–5 and 5–15 cm, respectively) and SPR (1.06 and 1.53 MPa at 0–5 and 5–15 cm, respectively) at both depths and increased the qs, Ksat and Green–Ampt estimated sorptivity (S) and hydraulic conductivity (Ks) parameters, and SWR (0–5 cm depth) at 0 and −0.4 kPa matric potentials (ψm). Furthermore, footslope position significantly decreased ρb, SPR at 0–5 and 5–15 cm depths, and increased the qs, Ksat, S, Ks, and SWR (0–5 cm depth) at every ψm ranged from 0 to −30.0 kPa. The higher N rate increased the coarse mesopores (60–1,000 μm) and total pores, whereas, footslope position increased the coarse mesopores, micropores (<60 μm), and total pores. Data from this study showed that planting switchgrass with 112 kg N/ha under footslope position helped in improving the soil hydrological properties, those can be beneficial in enhancing the biomass yield under marginal lands.

Climatic impact, future biomass production, and local adaptation of four switchgrass cultivars

AbstractPrevious studies have shown that switchgrass has a wide range of genetic variation and that productivity is linked to local adaptation to the location of origin for many cultivars. In this meta‐analysis, we compiled and analyzed 900 observations associated with 41 field trials for four switchgrass cultivars (two lowlands, Alamo and Kanlow, and two uplands, Cave‐In‐Rock and Shelter). This extensive dataset and machine learning were used to identify the most influential variables impacting switchgrass productivity, to search for evidence of local adaptation to each cultivar's location of origin, and to predict change in productivity under future climate for each cultivar. In general, variables associated with climate and management are more important predictors of productivity relative to soil variables. Three climatic variables, annual mean temperature, annual precipitation, and precipitation in the wettest month, are identified as key environmental variables for productivity of all cultivars. Productivity under future climate (2041–2060) is predicted to stay stable for all cultivars relative to the prediction under current climate (1986–2005) across all trial locations and over a 20‐year simulation period. However, the productivity of each cultivar varies from location to location and from year to year, although productivity varies more between locations than between years. Additionally, we observe shifts in the most productive cultivar at the local field scale depending on the combination of management practice and climates. The shape of the relationship between productivity and the annual mean temperature relative to the cultivar's location of origin is a bell‐shaped curve for Kanlow, Cave‐in‐Rock, and Shelter, indicative of local adaptation. Identifying influential environmental variables and their relationships to productivity with respect to cultivar's location of origin help predicting productivity on the local field scale, and will help with the biofuel production planning through the selection of suitable cultivars for different locations under climate changes.

Biochar compost blends facilitate switchgrass growth in mine soils by reducing Cd and Zn bioavailability

Biochars have the potential to reclaim mine-impacted soils; however, their variable physico-chemical properties incite speculation about their successful remediation performance. This investigation examined the capability of biochars produced from three different feedstocks along with a compost blend to improve switchgrass growth conditions in a mine-impacted soil by examining influences on soil pH, grass metal contents, and soil-extractable metal concentrations. Cadmium (Cd)- and zinc (Zn)-contaminated mine soil was collected from a site near Webb City, Missouri, USA—a location within the Tri-State Mining District. In a full factorial design, soil was treated with a 0%, 2.5%, and 5% (w/w) compost mixture (wood chips + beef cattle manure), and 0%, 2.5% and 5% of each biochar pyrolyzed from beef cattle manure, poultry litter, and lodgepole pine feedstocks. Switchgrass (Panicum virgatum, ‘Cave-In-Rock’ variety) was grown in a greenhouse for 50 days and the mass of shoots (above-ground biomass) and roots was assessed, while soil pH, deionized H2O- and 0.01 M CaCl2-extractable Cd and Zn concentrations were measured. Poultry litter biochar and compost had the greatest ability to raise soil pH (from 4.40 to 6.61), beef cattle manure biochar and compost moderately raised pH (from 4.4 to 5.92), and lodgepole pine biochar and compost weakly raised pH (from 4.40 to 5.05). Soils treated with beef cattle manure biochar, poultry litter biochar significantly reduced deionized H2O- and 0.01 M CaCl2-extractable Cd and Zn concentrations, while lodgepole pine biochar-treated soils showed mixed results. Switchgrass shoot and root masses were greatest in soil treated with compost in combination with either beef cattle manure biochar or poultry litter biochar. Soils treated with 5% beef cattle manure biochar + 5% compost had greater reductions in total Cd and Zn concentrations measured in switchgrass shoots and roots compared to the other two treatments. The three biochars and compost mixtures applied to heavy metal, mine-impacted soil had considerable performance dissimilarities for improving switchgrass productivity. Switchgrass growth was noticeably improved after treatment with the compost in combination with biochar from beef cattle manure or poultry litter. This may be explained by the increased soil pH that promoted Zn and Cd precipitation and organic functional groups that reduced soil-available heavy metal concentrations. Our results imply that creating designer biochars is an important management component in developing successful mine-site phytostabilization programs.

Spatial agent‐based modeling for dedicated energy crop adoption and cellulosic biofuel commercialization

AbstractDedicated bioenergy crops, such as perennial grass and short rotation trees, qualify as cellulosic biofuel feedstocks to meet the requirements for advanced biofuel according to the expanded Renewable Fuel Standard. The utilization of dedicated energy crops for cellulosic biofuels is still in the early stage, at pilot scale, and the existing cellulosic biorefineries are yet to be commercialized. This study develops an agent‐based model to simulate the spatial diffusion of switchgrass (Panicum virgatum L.) adoption in Indiana cropland from 2015 to 2027 under various biofuel market scenarios. Results indicate that it would be economically viable to produce 1.1 billion gallons (4.2 billion liters) cellulosic ethanol from switchgrass annually in Indiana until 2023, given an average annual farm‐gate price of $123.93 t−1 for the feedstock. This study also finds that the high productivity of switchgrass can increase the adoption rates of farmers and secure a stable feedstock supply. It also reveals that the high equipment costs required for scaling up production capacity and the high variable operating cost of cellulosic biofuel production will inhibit the viability of commercializing cellulosic biofuels with a stable supply of feedstock. Financial incentives for cellulosic biofuel production have a significant impact on promoting the adoption of dedicated energy crops in Indiana. This paper provides useful insights for biorefinery development and policy making to facilitate the commercialization of cellulosic biofuels by explaining the effects of the decisions of farmers on the adoption of dedicated energy crops. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Protocol for Agrobacterium-Mediated Transformation and Transgenic Plant Production of Switchgrass.

Switchgrass (Panicum virgatum L.) is one of the most important bioenergy crops for lignocellulose ethanol production. Molecular breeding provides a powerful tool to supplement conventional switchgrass breeding by introducing or editing genes of interest. In this chapter, we describe Agrobacterium tumefaciens-mediated transformation protocols for lowland tetraploid switchgrass cultivar Alamo.

Enhancement of methane production by addition of Clostridium thermocellum in the anaerobic digestion of switchgrass

The low efficiency of hydrolysis is usually the rate-limiting step in the anaerobic digestion of lignocellulosic substrates. In this investigation, bioaugmentation and pretreatment using the cellulolytic anaerobic bacterium Clostridium thermocellum have been found to be beneficial for the improvement of the hydrolysis of switchgrass and enhancing methane production. By adopting these two methods, the methane production of switchgrass reached 289.309 and 278.34 ml/g volatile solids, with an increase of 24.2% and 19.5%, respectively, compared to the blank group. The outcome of this study clearly indicated that the fermentation efficiency could be improved by the use of microorganisms in the above two methods. The methane yield of bioaugmentation not only was slightly higher than that of biopretreatment but also had a higher efficiency in terms of total time and was more adaptive to the industrial implementation. Moreover, this study proved that Clostridium thermocellum required about one week to acclimatize the anaerobic condition and the optimum adding time was at the beginning of anaerobic digestion.

Inter-Annual Precipitation Variability Decreases Switchgrass Productivity from Arid to Mesic Environments

Cellulosic biofuels are an important source of renewable biomass within the alternative energy portfolio. Switchgrass (Panicum virgatum L.), a perennial C4 grass native to North America, is widely studied as a biofuel feedstock for its consistently high yields and minimal input requirements. The influences of precipitation amount and temporal variability on the fertilizer response of switchgrass productivity are not fully understood. Moreover, global climate models predict changes in rainfall patterns towards lower and increasingly variable soil water availability in several productive areas worldwide, which may impact net primary production of biofuel crops. We conducted a meta-analysis of aboveground net primary production of switchgrass from 48 publications encompassing 82 different locations, 11 soil types, 52 switchgrass cultivars, fertilizer inputs between 0 to 896 kg N ha−1 year−1, and 1 to 6 years of annual productivity measures repeated on the same stand. Productivity of the lowland ecotype doubled with N rates > 131 kg N ha−1 year−1, but upland ecotype productivity increased only by 50%. Results showed an optimum N rate of 30 to 60 kg N ha−1 year−1 for both ecotypes, after which biomass gain per unit of N added decreased. Growing season precipitation (GSPPT) and inter-annual precipitation variability (inter-PPTvar) affected both ecotypes similarly. Long-term mean annual precipitation (MAP) differentially affected lowland and upland productivity, depending on the N level. Productivity responses to MAP and GSPPT were similar for both upland and lowland ecotypes at none or low N rates. When N increased beyond 60 kg N ha−1 year−1, lowland cultivars had a greater growth response to MAP than uplands. Productivity increased with increasing GSPPT and MAP and had a positive linear response to MAP ranging from 600 to 1200 mm year−1. One third of the variability in switchgrass production was accounted for by inter-PPTvar. After accounting for MAP, sites with higher inter-PPTvar had lower switchgrass productivity than sites with lower inter-PPTvar. Increased inter-annual variation in precipitation reduced production of both ecotypes. Predicted changes in the amount and timing of precipitation thus likely will exert greater influence on production of upland than lowland ecotypes of switchgrass.

Overexpression of gene encoding the key enzyme involved in proline-biosynthesis (PuP5CS) to improve salt tolerance in switchgrass (Panicum virgatum L.).

Genetic improvement through overexpressing PuP5CS in switchgrass is feasible for enhancing plant salt stress tolerance. Switchgrass (Panicum virgatum L.) has developed into a dedicated bioenergy crop. To improve the biomass production of switchgrass grown on different types of soil, abiotic stress tolerance traits are considered for its genetic improvement. Proline accumulation is a widespread response when plants are subjected to abiotic stresses such as drought, cold and salinity. In plants, P5CS gene encodes the key regulatory enzyme that plays a crucial role in proline biosynthesis. Here, we introduced the PuP5CS gene (from Puccinellia chinampoensis) into switchgrass by Agrobacterium-mediated transformation. Transgenic lines overexpressing the PuP5CS gene showed phenotypic advantages, in leaf width, internode diameter, internode length, tiller numbers and precocious flowering under normal conditions, and the transgenic lines displayed better regenerative capacity in forming more tillers after harvest. Moreover, the PuP5CS gene enhanced the salt tolerance of transgenic switchgrass by altering a wide range of physiological responses. In accordance with the physiological results, histological analysis of cross sections through the leaf blade showed that the areas of bulliform cells and bundle sheath cells were significantly increased in PuP5CS-overexpressing leaves. The expression levels of ROS scavenging-associated genes in transgenic plants were higher than in control plants under salt stress. The results show that genetic improvement through overexpressing PuP5CS in switchgrass is feasible for enhancing plant stress tolerance.

Perennial biomass production from marginal land in the Upper Mississippi River Basin

AbstractMarginal land is considered promising for biomass production. However, understanding on biomass crop growth and total biofuel production from this land type is very limited. This study evaluated potential production of switchgrass (Panicum virgatum) and Miscanthus (Miscanthus × giganteus) on marginal lands in the Upper Mississippi River Basin. A soil and water assessment tool model with detailed representation of marginal lands and their suitability for growth of the 2 grasses was setup. Marginal land was defined as cropland and grassland with land capability class from 3 to 8. All marginal lands were included as new land covers in the land use map and were preserved when HRUs were defined. The soil and water assessment tool model was calibrated for flow at 13 sites within the Upper Mississippi River Basin region at monthly scale. The predicted biomass by growing switchgrass and Miscanthus on marginal lands in the study area can produce up to 37% of the 132 × 109 L biofuel goal set by the 2010 Energy Independence and Security Act in the USA. The simulated flow was lower when marginal lands were converted to grow perennial bioenergy crops. The results from this study improved our understanding on growth of perennial crops on marginal land and their contributions to biofuel development.

Where can switchgrass production be more profitable than corn and soybean? An integrated subfield assessment in Iowa, USA

AbstractPerennial bioenergy crops are considered an important feedstock for a growing bioeconomy. However, in the USA, production of biofuel from these dedicated, nonfood crops is lagging behind federal mandates and markets have yet to develop. Most studies on the economic potential of perennial biofuel crops have concluded that even high‐yielding bioenergy grasses are unprofitable compared to corn/soybeans, the prevailing crops in the United States Corn Belt. However, they did not account for opportunities precision agriculture presents to integrate perennials into agronomically and economically underperforming parts of corn/soybean fields. Using publicly available subfield data and market projections, we identified an upper bound to the areas in Iowa, United States, where the conversion from corn/soybean cropland to an herbaceous bioenergy crop, switchgrass, could be economically viable under different price, land tenancy, and yield scenarios. Assuming owned land, medium crop prices, and a biomass price of US$ 55 Mg−1, we showed that 4.3% of corn/soybean cropland could break even when converted to switchgrass yielding up to 10.08 Mg ha−1. The annualized change in net present value on each converted subfield patch ranged from just above US$ 0 ha−1 to 692 ha−1. In the three counties of highest economic opportunity, total annualized producer benefits from converting corn/soybean to switchgrass summed to US$ 2.6 million, 3.4 million, and 7.6 million, respectively. This is the first study to quantify an upper bound to the potential private economic benefits from targeted conversion of unfavorable corn/soybean cropland to switchgrass, leaving arable land already under perennial cover unchanged. Broadly, we conclude that areas with high within‐field yield variation provide highest economic opportunities for switchgrass conversion. Our results are relevant for policy design intended to improve the sustainability of agricultural production. While focused on Iowa, this approach is applicable to other intensively farmed regions globally with similar data availability.

30 Years of Progress toward Increased Biomass Yield of Switchgrass and Big Bluestem

Breeding to improve biomass production of switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) for conversion to bioenergy began in 1992. The purpose of this study was (i) to develop a platform for uniform regional testing of cultivars and experimental populations for these species, and (ii) to estimate the gains made by breeding during 1992 to 2012. A total of 25 switchgrass populations and 16 big bluestem populations were planted in uniform regional trials at 13 locations in 2012 and 2014. The reference region was USDA Hardiness Zones 3 through 6 in the humid temperate United States. Significant progress toward increased biomass yield was made in big bluestem and within upland‐ecotype populations, lowland‐ecotype populations, and hybrid‐derived populations of switchgrass. Four mechanisms of increasing biomass yield were documented: (i) increased biomass yield per se, (ii) later flowering to extend the growing season, (iii) combined later flowering from the lowland ecotype with survivorship of the upland ecotype in hybrid‐derived populations, and (iv) increased survivorship of late‐flowering lowland populations in hardiness zones that represent an expansion of their natural adaption zone. Switchgrass exhibited all four mechanisms in one or more improved populations, whereas improved populations of big bluestem were likely influenced by two of the four mechanisms. The uniform testing program was successful at documenting increases in biomass yield, identifying the mechanisms for increased yield, and determining adaptation characteristics and limitations of improved populations.

Mapping cropland waterway buffers for switchgrass development in the eastern Great Plains, USA

AbstractSwitchgrass (Panicum virgatum L.), a highly productive perennial grass, has been recommended as one potential source for cellulosic biofuel feedstocks. Previous studies indicate that planting perennial grasses (e.g., switchgrass) in high‐topographic‐relief cropland waterway buffers can improve local environmental conditions and sustainability. The main advantages of this land management practice include (i) reducing soil erosion and improving water quality because switchgrass requires less tillage, fertilizers, and pesticides; and (ii) improving regional ecosystem services (e.g., improving water infiltration, minimizing drought and flood impacts on production, and serving as carbon sinks). In this study, we mapped high‐topographic‐relief cropland waterway buffers with high switchgrass productivity potential that may be suitable for switchgrass development in the eastern Great Plains (EGP). The US Geological Survey (USGS) Compound Topographic Index map, National Land Cover Database 2011, USGS irrigation map, and a switchgrass biomass productivity map derived from a previous study were used to identify the switchgrass potential areas. Results show that about 16 342 km2 (c. 1.3% of the total study area) of cropland waterway buffers in the EGP are potentially suitable for switchgrass development. The total annual estimated switchgrass biomass production for these suitable areas is approximately 15 million metric tons. Results from this study provide useful information on EGP areas with good cellulosic switchgrass biomass production potential and synergistic substantial potential for improvement of ecosystem services.