Farm-Scale Cost of Producing Perennial Energy Cane as a Biofuel Feedstock

Energy cane varieties are high-fiber sugarcane clones which represent a promising feedstock in the production of alternative biofuels and biobased products. This study explored the crop establishment and whole farm production costs of growing energy cane as a biofuel feedstock in the southeastern USA. More specifically, total production costs on a feedstock dry matter biomass basis were estimated for five perennial energy cane varieties over alternative crop cycle lengths. Variable production costs for energy cane production were estimated to be in the $63 to $76 Mg^?1 range of biomass dry matter for crop cycles through harvest of fourth through sixth stubble crops. Total production costs, including charges for fixed equipment costs, general farm overhead, and land rent, were estimated to range between $105 and $127 Mg^?1 of feedstock biomass dry matter material.     

Economic Feasibility of Using Switchgrass Pasture to Produce Beef Cattle Gain and Bioenergy Feedstock

Integration of switchgrass (Panicum virgatum L.) into livestock production systems has potential to improve farm economics and encourage development of a biofuel industry in the Southern Great Plains. The objectives of this study were to determine the economics of seven alternative switchgrass grazing and bioenergy feedstock systems and to determine how sensitive the results are among the systems for a range of cattle and feedstock prices. Data were collected from a completely randomized designed grazing study in south-central Oklahoma in 2008, 2009, and 2010. Stocking density treatments [0, 2.5, 4.9 and 7.4 hd ha^?1] were randomly assigned to 12 0.81-ha switchgrass pastures. Using biological data from the field trial, economic data collected from the marketplace and assumptions about prices of bioenergy feedstock, seven production systems were simulated. The systems included no-graze feedstock only (NG/FS); graze lightly no feedstock (GL/NF); graze moderately no feedstock (GM/NF); graze heavily no feedstock H/NF)]; lightly grazed plus feedstock (GL/F); moderately grazed plus feedstock (GM/F); and heavily grazed plus feedstock (GH/F). Enterprise budgeting was used to compute expected net returns for the seven systems. Random-effects mixed ANOVA models were used to determine the effects of production system on yield, gain, and net return. At a feedstock price $0 Mg^?1, the GM/NF was the most profitable ($45 ha^?1) system. At feedstock prices of $55 and $83 Mg^?1, the GL/F system realized net returns of $232 and $523 ha^?1, respectively, and for feedstock prices >$83 Mg^?1, the NG/FS system was determined to be most economical.     

Farm-Scale Production Cost of Switchgrass for Biomass

The economic potential of cellulosic biomass from switchgrass has heretofore been evaluated using estimates of farm costs based on extrapolation from experimental data and budget estimates. The objective of the project reported here was to estimate the cost of production that would be experienced by farmers on commercial production situations. Switchgrass was produced as a biomass crop on commercial-scale fields by ten contracting farmers located from northern North Dakota to southern Nebraska. Results showed a wide range of yields and costs across the five production years and ten sites, with an overall average cost of $65.86 Mg^?1 of biomass dry matter, and annualized yield of 5.0 Mg ha^?1. The low-cost half of the producers were able to produce at an average cost of $51.95 Mg^?1over the 5-year period. When projected to a full 10-year rotation, their cost fell further to $46.26 Mg^?1. We conclude that substantial quantities of biomass feedstock could have been produced in this region at a cost of about $50 Mg^?1 at the farm gate, which translates to about $0.13/l of ethanol. These results provide a more reliable benchmark for current commercial production costs as compared to other estimates, which range from $25 to $100 Mg^?1.     

Determining Switchgrass Breakeven Prices in a Landscape Design System

Precision agriculture technologies allow producers to identify areas of fields that are underperforming and unprofitable. If these less productive parts of the field could be converted to a bioenergy crop through subfield management strategies (landscape design), there may be potential gains to farmer revenue, biomass availability, and reduced adverse environmental impacts. Switchgrass is considered as a potential energy crop due its ability to thrive in marginal conditions. Previous studies have examined switchgrass production and breakeven costs, but have not looked at how production costs may change when produced in a landscape design situation. Adapting costs to the partial field situation, this paper determines the switchgrass breakeven prices ($ ton^?1) which equate producers’ net revenues in a base case (all corn) and landscape design case. That breakeven price is the price at which the farmer would be indifferent between the base and landscape design cases. We examine the case of a general, 100-acre field in Iowa, with 15 acres converted to switchgrass production, as well as 11 actual fields in Central Iowa where unprofitable subfields are assumed to be converted to switchgrass production, and the remaining portion of the field remains in corn. We find an average switchgrass breakeven price of $173 ton^?1 when land costs are included, and an average of $114 ton^?1 when no land costs are considered. A stochastic analysis to obtain a distribution of switchgrass breakeven prices under uncertainty is performed, producing distributions of switchgrass breakeven prices of $65–$266 ton^?1 and $108– $432 ton^?1 with and without land costs, respectively.     

Economic Competitiveness of Napier Grass in Irrigated and Non-irrigated Georgia Coastal Plain Cropping Systems

Interest and focus on development of renewable biofuels has been increasing over the past decade leading to the introduction of a wide cadre of renewable feedstocks. As a result, numerous perennial warm-season grasses have been introduced and management practices evaluated to determine their suitability as biofuel feedstocks. “Merkeron” napier grass (Pennisetum purpureum) plots were established in 2010 and harvested during crop years 2011 through 2015 adjacent to an on-going peanut (Arachis hypogaea L.), corn (Zea mays L.), and cotton (Gossypium hirsutum L.) cropping systems study conducted at the USDA/ARS Multi-crop Irrigation Research Farm in Shellman, GA (84 36 W, 30 44 N) on a Greenville fine sandy loam (fine, kaolinitic, thermic Rhodic Kandiudults). Napier grass was produced in both non-irrigated and two irrigated levels with different levels of nitrogen and potassium fertilizers. Peanut, corn, and cotton were produced in non-irrigated and full irrigation regimes. Breakeven prices for napier grass ranged from $65 to $84 Mg^?1 at variable and total costs. The breakeven napier grass price was estimated such that the net returns were equal between napier grass and peanut, cotton, corn cropping systems. At variable production cost, comparative breakeven napier grass prices for non-irrigated, 50% irrigated, and full irrigated regimes were $77, $117, and $112 Mg^?1, respectively. Napier grass did not compete economically against traditional irrigated cropping systems. Depending on traditional crop prices and bioenergy feed stock prices, napier grass could offer economic opportunities in non-irrigated production environments, riparian buffer zone edges, or non-cropped marginal production areas.     

Economics of Alternative Fertilizer Supply Systems for Switchgrass Produced in Phosphorus-Deficient Soils for Bioenergy Feedstock

Limited information is available explaining the economics of supplying N and P fertilizers on established stands of switchgrass growing in phosphorus-deficient soils. The objective of this study was to determine the most economical fertilizer supply system for producing feedstock in phosphorus-deficient soil in the southern Great Plains. Data collected from field trials conducted at two locations in south-central Oklahoma along with prices quoted by local input suppliers and custom service providers and assumptions about the farm-gate price of feedstock were used to estimate expected values for production costs, gross revenue and net return to owner's labor, management, and overhead for eight fertilizer supply systems. The systems included a zero fertilizer check system (0/0), three P systems (0/34, 0/67, and 0/101), one N system (135/0), and three N and P systems (135/34, 135/67, and 135/101). Random-effects mixed ANOVA models were used to determine the effects of fertilizer system on the values of total cost and net return. For the base-case price scenario (feedstock, N and P prices of $110 Mg^?1 and $1.28 and 1.17 kg^?1, respectively), the 135/0 system was the most profitable system, producing 10.2 Mg of feedstock and $263 of net return per hectare. Economic results were most sensitive to the prices of feedstock, N and P. Net return was negative for all eight systems for the scenario where the farm-gate price of feedstock was relatively low ($55 Mg^?1) and prices for N and P were relatively high ($2.20 kg^?1).     

Impacts of management practices on bioenergy feedstock yield and economic feasibility on Conservation Reserve Program grasslands

Perennial grass mixtures planted on Conservation Reserve Program (CRP) land are a potential source of dedicated bioenergy feedstock. Long‐term nitrogen (N) and harvest management are critical factors for maximizing biomass yield while maintaining the longevity of grass stands. A six‐year farm‐scale study was conducted to understand the impact of weather variability on biomass yield, determine optimal N fertilization and harvest timing management practices for sustainable biomass production, and estimate economic viability at six CRP sites in the United States. Precipitation during the growing season was a critical factor for annual biomass production across all regions, and annual biomass production was severely reduced when growing season precipitation was below 50% of average. The N rate of 112 kg ha^?1 produced the highest biomass yield at each location. Harvest timing resulting in the highest biomass yield was site‐specific and was a factor of predominant grass type, seasonal precipitation, and the number of harvests taken per year. The use of N fertilizer for yield enhancement unambiguously increased the cost of biomass regardless of the harvest timing for all six sites. The breakeven price of biomass at the farmgate ranged from $37 to $311 Mg^?1 depending on the rate of N application, timing of harvesting, and location when foregone opportunity costs were not considered. Breakeven prices ranged from $69 to $526 Mg^?1 when the loss of CRP land rental payments was included as an opportunity cost. Annual cost of the CRP to the federal government could be reduced by over 8% in the states included in this study; however, this would require the biomass price to be much higher than in the case where the landowner receives the CRP land rent. This field research demonstrated the importance of long‐term, farm‐scale research for accurate estimation of biomass feedstock production and economic viability from perennial grasslands.     

Evaluating Local Crop Residue Biomass Supply: Economic and Environmental Impacts

The increasing interest in energy production from biomass requires a better understanding of potential local production and environmental impacts. This information is needed by local producers, biomass industry, and other stakeholders, and for larger scale analyses. This study models biomass production decisions at the field level using a case example of a biomass gasification facility constructed at the University of Minnesota??Morris (UMM). This institutional-scale application has an anticipated feedstock demand of about 8,000?Mg?year^?1. The model includes spatial impacts due to sub-field variation in soil characteristics and transportation costs. Results show that the amount of biomass producers could profitably supply within a 32.2-km radius of UMM increases as plant-gate biomass price increases from $59 to $84?Mg^?1, with 588,000?Mg annual biomass supply at $84?Mg^?1. Results also show that the most profitable tillage and crop rotation practices shift in response to increasing biomass price with producers shifting from a corn-soybean rotation toward continuous corn. While biomass harvest is conducive to increased soil erosion rates and reduced soil organic carbon levels, changes in crop production practices are shown to at least partially offset these impacts. Transportation costs tend to concentrate and intensify biomass production near the biomass facility, which also tends to concentrate environmental impacts near the facility.     

Nutrient Removal as a Function of Corn Stover Cutting Height and Cob Harvest

One-pass harvest equipment has been developed to collect corn (Zea mays L.) grain, stover, and cobs that can be used as bioenergy feedstock. Nutrients removed in these feedstocks have soil fertility implication and affect feedstock quality. The study objectives were to quantify nutrient concentrations and potential removal as a function of cutting height, plant organ, and physiological stage. Plant samples were collected in 10-cm increments at seven diverse geographic locations at two maturities and analyzed for multiple elements. At grain harvest, nutrient concentration averaged 5.5 g?N kg^?1, 0.5 g?P kg^?1, and 6.2 g?K kg^?1 in cobs, 7.5 g?N kg^?1, 1.2 g?P kg^?1, and 8.7 g?K kg^?1 in the above-ear stover fraction, and 6.4 g?N kg^?1, 1.0 g?P kg^?1, and 10.7 g?K kg^?1 in the below-ear stover fraction (stover fractions exclude cobs). The average collective cost to replace N, P, and K was $11.66 Mg^?1 for cobs, $17.59 Mg^?1 for above-ear stover, and $18.11 Mg^?1 for below-ear stover. If 3 Mg ha^?1 of above-ear stover fraction plus 1 Mg of cobs are harvested, an average N, P, and K replacement cost was estimated at $64 ha^?1. Collecting cobs or above-ear stover fraction may provide a higher quality feedstock while removing fewer nutrients compared to whole stover removal. This information will enable producers to balance soil fertility by adjusting fertilizer rates and to sustain soil quality by predicting C removal for different harvest scenarios. It also provides elemental information to the bioenergy industry.     

An integrated biogeochemical and economic analysis of bioenergy crops in the Midwestern United States

This study integrates a biophysical model with a county‐specific economic analysis of breakeven prices of bioenergy crop production to assess the biophysical and economic potential of biofuel production in the Midwestern United States. The bioenergy crops considered in this study include a genotype of Miscanthus, Miscanthus×giganteus, and the Cave‐in‐Rock breed of switchgrass (Panicum virgatum). The estimated average peak biomass yield for miscanthus in the Midwestern states ranges between 7 and 48 metric tons dry matter per hectare per year ( t DM ha^?1 yr^?1), while that for switchgrass is between 10 and 16 t DM ha^?1 yr^?1. With the exception of Minnesota and Wisconsin, where miscanthus yields are likely to be low due to cold soil temperatures, the yield of miscanthus is on average more than two times higher than yield of switchgrass. We find that the breakeven price, which includes the cost of producing the crop and the opportunity cost of land, of producing miscanthus ranges from $53 t^?1 DM in Missouri to $153 t^?1 DM in Minnesota in the low‐cost scenario. Corresponding costs for switchgrass are $88 t^?1 DM in Missouri to $144 t^?1 DM in Minnesota. In the high‐cost scenario, the lowest cost for miscanthus is $85 t^?1 DM and for switchgrass is $118 t^?1 DM, both in Missouri. These two scenarios differ in their assumptions about ease of establishing the perennial crops, nutrient requirements and harvesting costs and losses. The differences in the breakeven prices across states and across crops are mainly driven by bioenergy and row crop yields per hectare. Our results suggest that while high yields per unit of land of bioenergy crops are critical for the competitiveness of bioenergy feedstocks, the yields of the row crops they seek to displace are also an important consideration. Even high yielding crops, such as miscanthus, are likely to be economically attractive only in some locations in the Midwest given the high yields of corn and soybean in the region.     

Maize Kernel Hardness,Endosperm Zein Profiles,and Ethanol Production

Maize (Zea mays L.) grain is an important feedstock for the ethanol-producing industry. However, little is known about the optimum grain quality for optimizing ethanol yielding efficiencies. We specifically investigated the response of ethanol yields (L Mg^?1) to kernel hardness, and its physiological determinant endosperm zein protein profiles, as affected by genotype selection, field nitrogen (N) fertilization, and crop growth environment. We measured ethanol yield and related this to different kernel hardness indicators, kernel composition, and zein profiles. We also described changes in field ethanol yield (L ha^?1), by taking into account the crop yield (Mg ha^?1). Hard endosperm genotypes always yielded less ethanol than softer endosperm ones per grain mass (L Mg^?1). Higher N fertilization rates increased kernel hardness and decreased ethanol yield (L Mg^?1) on soft endosperm dented genotypes but had no effect on hard endosperm ones. Ethanol yield was negatively correlated with kernel density, kernel protein concentration, and Z1 and Z2 zein fractions. Within Z2, 15 kDa β-zein explained the largest ethanol yield variation generated by genotypes, N fertilizations, and growth environments. However, and although these differences were as large as 10%, ethanol field yield (L ha^?1) was mainly driven by crop yields (r ² 0.98) due to the large crop yield (Mg ha^?1) differences observed across treatments. Together, our results helped describe the magnitude that changes in maize kernel hardness can have over ethanol yield, both through genotype selection or crop management. A particular Z2 zein protein rises as relevant for future genetic manipulations of maize ethanol yield determination.     

Quantifying Actual and Theoretical Ethanol Yields for Switchgrass Strains Using NIRS Analyses

Quantifying actual and theoretical ethanol yields from biomass conversion processes such as simultanteous saccharification and fermentation (SSF) requires expensive, complex fermentation assays, and extensive compositional analyses of the biomass sample. Near-infrared reflectance spectroscopy (NIRS) is a non-destructive technology that can be used to obtain rapid, low-cost, high-throughput, and accurate estimates of agricultural product composition. In this study, broad-based NIRS calibrations were developed for switchgrass biomass that can be used to estimate over 20 components including cell wall and soluble sugars and also ethanol production and pentose sugars released as measured using a laboratory SSF procedure. With this information, an additional 13 complex feedstock traits can be determined including theoretical and actual ethanol yields from hexose fermentation. The NIRS calibrations were used to estimate feedstock composition and conversion information for biomass samples from a multi-year switchgrass (Panicum virgatum L.) biomass cultivar evaluation trial. There were significant differences among switchgrass strains for all biomass conversion and composition traits including actual ethanol yields, ETOHL (L Mg^?1) and theoretical ethanol yields, ETOHTL (L Mg^?1), based on cell wall and non-cell wall composition NIRS analyses. ETOHL means ranged from 98 to 115 L Mg^?1 while ETOHTL means ranged from 203 to 222 L Mg^?1. Because of differences in both biomass yields and conversion efficiency, there were significant differences among strains for both actual (2,534?C3,720 L ha^?1) and theoretical (4,878?C7,888 L ha^?1) ethanol production per hectare. It should be feasible to improve ethanol yields per hectare by improving both biomass yield and conversion efficiency by using NIRS analyses to quantify differences among cultivars and management practices.     

Improving the Profitability of Willow Crops��Identifying Opportunities with a Crop Budget Model

Short-rotation woody crops like shrub willow are a potential source of biomass for energy generation and bioproducts. However, since willow crops are not widely grown in North America, the economics of this crop and the impacts of key crop production and management components are not well understood. We developed a budget model, EcoWillow v1.4 (Beta), that allows users to analyze the entire production-chain for willow systems from the establishment to the delivery of wood chips to the end-user. EcoWillow was used to analyze how yield, crop management options, land rent, fuel, labor, and other costs influence the Internal Rate of Return (IRR) of willow crop systems in upstate New York. We further identified cost variables with the greatest potential for reducing production and transport costs of willow biomass. Productivity of 12 oven-dried tons (odt) ha^?1 year^?1 and a biomass price of $ (US dollars) 60 odt^?1 results in an IRR of 5.5%. Establishment, harvesting, and transportation operations account for 71% of total costs. Increases in willow yield, rotation length, and truck capacity as well as a reduction in harvester down time, land costs, planting material costs, and planting densities can improve the profitability of the system. Results indicate that planting speed and fuel and labor costs have a minimal effect on the profitability of willow biomass crops. To improve profitability, efforts should concentrate on (1) reducing planting stock costs, (2) increasing yields, (3) optimizing harvesting operations, and (4) co-development of plantation designs with new high-yielding clones to reduce planting density.     

Site-Specific Trade-offs of Harvesting Cereal Residues as Biofuel Feedstocks in Dryland Annual Cropping Systems of the Pacific Northwest,USA

Cereal residues are considered an important feedstock for future biofuel production. Harvesting residues, however, could lead to serious soil degradation and impaired agroecosystem services. Our objective was to evaluate trade-offs of harvesting wheat and barley residues including impacts on soil erosion and quality, soil organic C (SOC), and nutrient removal. We used agricultural data from 369 geo-referenced points on the 37-ha Washington State University Cook Agronomy Farm combined with model simulations to develop straw harvest scenarios for conventional tillage (CT) and no-tillage (NT) and both 2- and 3-year crop rotations with sequences of wheat, barley, and peas. Site-specific estimates of ethanol production from 2- and 3-year rotation scenarios ranged from 681 to 1,541 L ha^?1 yr^?1, indicating that both crop rotation and site-specific targeting of residue harvest are important factors. Harvesting straw reduced residue C inputs by 46 % and resulted in levels below that required to maintain SOC under CT. This occurred as a function of both straw harvest and low residue producing crops in rotation. Harvesting straw under CT was predicted to reduce soil quality as Soil Conditioning Indices (SCIs) were negative throughout the field. In contrast, SCIs under NT were positive despite straw harvest. Replacement value of nutrients (N, P, K, S) removed in harvested straw averaged $14.54 Mg^?1 dry straw and ranged from $36.04 to $80.30 ha^?1, while straw harvesting costs averaged $34.25 Mg^?1, and the current (2014) market value of straw is $65 Mg^?1. We concluded that substantial trade-offs exist in harvesting straw for biofuel, that trade-offs should be evaluated on a site-specific basis, and that support practices such as crop rotation, reduced tillage, and site-specific nutrient management need to be considered if residue harvest is to be sustainable.     

Profitability of Willow Biomass Crops Affected by Incentive Programs

The economics of willow biomass crops are strongly influenced by yield, production, and harvesting costs and the delivered price for biomass. Under current management practices, willow biomass crops with yields of 12 oven-dried metric tons (odt)?ha^?1 year^?1 and a delivered price of $60 odt^?1 have an internal rate of return (IRR) of about 5.5 %. Yields below 9 odt ha^?1 year^?1 have an IRR <0 %. We examined the impact of different incentive programs on the returns from willow biomass crops and the hectares or tons of willow biomass supported across a range of yields. Incentive programs examined included establishment grants (EG), annual payments (AIP), low cost startup loans, and matching payments offered by two existing programs, the Conservation Resource Program (CRP) and more recently the Biomass Crop Assistance Program (BCAP). EGs covering 75 % of the establishment costs provide high returns for growers on medium to high-productivity sites. Stand-alone AIPs with payments of $124 ha^?1 year^?1 paid over 5–15 years had little impact on profitability for growers but were costly for a funding agency. Low-cost loans with an interest rate of 2–4 % are one of the least expensive approaches ($1.3–6.6 odt^?1) and improve profitability for medium- and high-yielding (8–16 odt ha^?1 year^?1) sites. A matching payment incentive providing $50 per odt delivered was the only individual incentive approach that made low-yielding sites (6 odt ha^?1 year^?1) profitable but was costly per odt compared to other incentives. Current CRP incentives made willow profitable across all productivity scenarios. The BCAP program generates higher profits for all productivity scenarios but comes at a higher cost. Effective financial incentives need to be well designed and monitored so that the target audience is reached and the intended policy goals are attained.     

Development of Sustainable Corn Stover Harvest Strategies for Cellulosic Ethanol Production

To prepare for a 2014 launch of commercial scale cellulosic ethanol production from corn/maize (Zea mays L.) stover, POET-DSM near Emmetsburg, IA has been working with farmers, researchers, and equipment dealers through “Project Liberty” on harvest, transportation, and storage logistics of corn stover for the past several years. Our objective was to evaluate seven stover harvest strategies within a 50-ha (125 acres) site on very deep, moderately well to poorly drained Mollisols, developed in calcareous glacial till. The treatments included the following: conventional grain harvest (no stover harvest), grain plus a second-pass rake and bale stover harvest, and single-pass grain plus cob-only biomass, grain plus vegetative material other than grain [(MOG) consisting of cobs, husks, and upper plant parts], grain plus all vegetative material from the ear shank upward (high cut), and all vegetative material above a 10 cm stubble height (low cut), with a John Deere 9750 STS combine, and grain plus direct baling of MOG with an AgCo harvesting system. Average grain yields were 11.4, 10.1, 9.7, and 9.5 Mg ha^?1 for 2008, 2009, 2010, and 2011, respectively. Average stover harvest ranged from 0 to 5.6 Mg ha^?1 and increased N, P, and K removal by an average of 11, 1.6, and 15 kg Mg^?1, respectively. Grain yield in 2009 showed a significant positive response to higher 2008 stover removal rates, but grain yield was not increased in 2010 or 2011 due to prior-year stover harvest. High field losses caused the direct-bale treatment to have significantly lower grain yield in 2011 because the AgCo system could not pick up the severely lodged crop. We conclude that decreases in grain yield across the 4 years were due more to seasonal weather patterns, spatial variability, and not rotating crops than to stover harvest.     

Economic Evaluation of Switchgrass Feedstock Production Systems Tested in Potassium-Deficient Soils

Limited information is available about the economic benefits and costs associated with managing switchgrass (Panicum virgatum L.) produced for bioenergy feedstock in the K-deficient soils common in the southern Great Plains. The objectives of this study were to determine the most economical production system for harvesting and managing N and K fertilizations on switchgrass stands and to determine how sensitive the results are to various feedstock and fertilizer market price scenarios. A 4-year agronomic field experiment was conducted on a K-deficient site in South Central Oklahoma; the treatments included two harvest systems (summer and winter (SW) and winter only (W)), two N rates (0 and 135 kg ha^?1), and two K rates (0 and 67 kg ha^?1). Enterprise budgeting techniques and mixed ANOVA models were used to determine and compare the effects of eight harvest/N/K systems on yield, total cost, revenue, and net return. The harvest/N/K systems evaluated included SW/0/0, SW/0/67, SW/135/0, SW/135/67, W/0/0, W/0/67, W/135/0, and W/135/67. Results revealed the SW/135/67 system produced significantly (P?>?0.0001) greater average yield compared to the other systems; however, the SW/0/0 system was the most (P?>?0.0001) economical, realizing an average net return of $415 ha^?1. Compared to the base–case net return of the SW/0/0 system, the value of the additional yield generated with the SW/135/67 system was less than the costs associated with the extra nutrients and additional harvest activity. For feedstock prices greater than $110 Mg^?1, the most economical system shifted from the SW/0/0 to favor the SW/135/67 system.     

Switchgrass nitrogen response and estimated production costs on diverse sites

Switchgrass (Panicum virgatum L.) has been the principal perennial herbaceous crop investigated for bioenergy production in North America given its high production potential, relatively low input requirements, and potential suitability for use on marginal lands. Few large trials have determined switchgrass yields at field scale on marginal lands, including analysis of production costs. Thus, a field‐scale study was conducted to develop realistic yield and cost estimates for diverse regions of the USA. Objectives included measuring switchgrass response to fertility treatments (0, 56, and 112 kg N ha^?1) and generating corresponding estimates of production costs for sites with diverse soil and climatic conditions. Trials occurred in Iowa, New York, Oklahoma, South Dakota, and Virginia, USA. Cultivars and management practices were site specific, and field‐scale equipment was used for all management practices. Input costs were estimated using final harvest‐year (2015) prices, and equipment operation costs were estimated with the MachData model ($2015). Switchgrass yields generally were below those reported elsewhere, averaging 6.3 Mg ha^?1 across sites and treatments. Establishment stand percent ranged from 28% to 76% and was linked to initial year production. No response to N was observed at any site in the first production year. In subsequent seasons, N generally increased yields on well‐drained soils; however, responses to N were nil or negative on less well‐drained soils. Greatest percent increases in response to 112 kg N ha^?1 were 57% and 76% on well‐drained South Dakota and Virginia sites, where breakeven prices to justify N applications were over $70 and $63 Mg^?1, respectively. For some sites, typically promoted N application rates may be economically unjustified; it remains unknown whether a bioenergy industry can support the breakeven prices estimated for sites where N inputs had positive effects on switchgrass yield.     

Multilocation Corn Stover Harvest Effects on Crop Yields and Nutrient Removal

Corn (Zea mays L.) stover was identified as an important feedstock for cellulosic bioenergy production because of the extensive area upon which the crop is already grown. This report summarizes 239 site-years of field research examining effects of zero, moderate, and high stover removal rates at 36 sites in seven different states. Grain and stover yields from all sites as well as N, P, and K removal from 28 sites are summarized for nine longitude and six latitude bands, two tillage practices (conventional vs no tillage), two stover-harvest methods (machine vs calculated), and two crop rotations {continuous corn (maize) vs corn/soybean [Glycine max (L.) Merr.]}. Mean grain yields ranged from 5.0 to 12.0 Mg ha^?1 (80 to 192 bu ac^?1). Harvesting an average of 3.9 or 7.2 Mg ha^?1 (1.7 or 3.2 tons ac^?1) of the corn stover resulted in a slight increase in grain yield at 57 and 51 % of the sites, respectively. Average no-till grain yields were significantly lower than with conventional tillage when stover was not harvested, but not when it was collected. Plant samples collected between physiological maturity and combine harvest showed that compared to not harvesting stover, N, P, and K removal was increased by 24, 2.7, and 31 kg ha^?1, respectively, with moderate (3.9 Mg ha^?1) harvest and by 47, 5.5, and 62 kg ha^?1, respectively, with high (7.2 Mg ha^?1) removal. This data will be useful for verifying simulation models and available corn stover feedstock projections, but is too variable for planning site-specific stover harvest.     

Screening Perennial Warm-Season Bioenergy Crops as an Alternative for Phytoremediation of Excess Soil P

A recent alternative strategy to reduce environmental problems associated with P transport from agricultural soils is the use of bioenergy crops to remediate excess soil P. In addition to the positive impacts associated with P mitigation, harvested biomass used as a renewable energy source can also offset the cost associated with plant-based P remediation strategies. The objective of this study was to identify potential crop species that can be used for remediation of soil P and as a cellulosic feedstock for production of renewable energy in South Florida. Fifteen crop entries were investigated for their potential to remove P from a P-enriched soil. Dry matter (DM) yield varied among crop species with greatest yield observed for elephantgrass (Pennisetum purpureum Schum.) and sugarcane (Saccharum spp.) (43 and 39 Mg?ha^?1 year^?1, respectively). Similarly, greater P removal rates were observed for elephantgrass (up to 126 kg?P?ha^?1 year^?1 in 2008) followed by sugarcane (62 kg?P?ha^?1 year^?1 in 2008). Although there was no effect (P?=?0.45) of crop species on P reduction in the soil, soil P concentrations decreased linearly during the 3-year study. Because of its relatively greater DM yield and P removal rates, elephantgrass was shown to be a good candidate for remediation of excess soil P in South Florida Spodosols.