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.     

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

Perennial 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.     

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.     

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.     

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.     

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).     

Crop Residue Harvest Economics: An Iowa and North Dakota Case Study

Rigorous economic analyses are crucial for the successful launch of lignocellulosic bioenergy facilities in 2014 and beyond. Our objectives are to (1) introduce readers to a query tool developed to use data downloaded from the Agricultural Research Service (ARS) REAPnet for constructing enterprise budgets and (2) demonstrate the use of the query tool with REAPnet data from two field research sites (Ames, IA, and Mandan, ND) for evaluating short-term economic performance of various biofuel feedstock production strategies. Our results for both sites showed that short-term (<3 years) impacts on grain profitability were lower at lower average annual crop residue removal rates. However, it will be important to monitor longer term changes to see if grain profitability declines over time and if biomass harvest degrades soil resources. Analyses for Iowa showed short-term breakeven field-edge biomass prices of $26–$42 Mg^?1 among the most efficient strategies, while results for North Dakota showed breakeven prices of $54–$73 Mg^?1. We suggest that development of the data query tool is important because it helps illustrate several different soil and crop management strategies that could be used to provide sustainable feedstock supplies.     

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.     

A spatial model of climate change effects on yields and break‐even prices of switchgrass and miscanthus in Ontario,Canada

Concerns over global climate change have led many jurisdictions to implement strategies aimed at reducing greenhouse gas levels. One example is the replacement of coal with dedicated energy crops, such as switchgrass and miscanthus. The yields and costs of these potentially valuable bio‐energy crops have been evaluated in only a few cases, and previous studies have not focused on climate change effects. This article assesses the potential yields and costs of growing switchgrass and miscanthus on the agricultural land base in Ontario, Canada, under different climate assumptions, using a GIS‐based integrated biophysical and economic simulation model. The model shows that miscanthus has a mean peak yield that is 88.5% (29.6 t ha^?1 compared with 15.7 t ha^?1) higher and a mean farm gate break‐even price that is 25.9% ($58.20 per tonne compared with $73.29 per tonne) lower than switchgrass. The impact of climate change on the yield and break‐even price of switchgrass and miscanthus is dependent upon the climate model. CGCM3.1 predicts that mean peak yields of switchgrass and miscanthus could drop by 17.8% and 14.9%, whereas CCSM3.0 predicts that mean yields could increase to 41.4% and 44.9%, from 2071 to 2100, in the A2 climate scenario respectively. Both crops show promise as biomass sources for bio‐energy production, but a changing global climate, along with cultivar and planting technology developments, could affect crop choices.     

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.     

The Economics of Biomass Collection and Transportation and Its Supply to Indiana Cellulosic and Electric Utility Facilities

With cellulosic energy production from biomass becoming popular in renewable energy research, agricultural producers may be called upon to plant and collect corn stover or harvest switchgrass to supply feedstocks to nearby facilities. Determining the production and transportation cost to the producer of corn stover or switchgrass and the amount available within a given distance from the plant will result in a per metric ton cost the plant will need to pay producers in order to receive sufficient quantities of biomass. This research computes up-to-date biomass production costs using recent prices for all important cost components including seed, fertilizer, herbicide, mowing/shredding, raking, baling, storage, handling, and transportation. The cost estimates also include nutrient replacement for corn stover. The total per metric ton cost is a combination of these cost components depending on whether equipment is owned or custom hired, what baling options are used, the size of the farm, and the transport distance. Total costs per dry metric ton for biomass with a transportation distance of 60 km ranges between $63 and $75 for corn stover and $80 and $96 for switchgrass. Using the county quantity data and this cost information, we then estimate biomass supply curves for three Indiana coal-fired electric utilities. This supply framework can be applied to plants of any size, location, and type, such as future cellulosic ethanol plants. Finally, greenhouse gas emissions reductions are estimated from using biomass instead of coal for part of the utility energy and also the carbon tax required to make the biomass and coal costs equivalent. Depending on the assumed CO₂ price, the use of biomass instead of coal is found to decrease overall costs in most cases.     

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.     

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.     

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.     

Crop Management Impacts Biofuel Quality: Influence of Switchgrass Harvest Time on Yield, Nitrogen and Ash of Fast Pyrolysis Products

Although upgrading bio-oil from fast pyrolysis of biomass is an attractive pathway for biofuel production, nitrogen (N) and mineral matter carried over from the feedstock to the bio-oil represents a serious contaminant in the process. Reducing the N and ash content of biomass feedstocks would improve process reliability and reduce production costs of pyrolytic biofuels. This study investigated: (1) How does switchgrass harvest date influence the yield, N concentration ([N]), and ash concentration of biomass and fast pyrolysis products? and (2) Is there a predictive relationship between [N] of switchgrass biomass and [N] of fast pyrolysis products? Switchgrass from five harvest dates and varying [N] from central Iowa were pyrolyzed using a free-fall reactor. Harvestable biomass peaked in August (8.6 Mg ha^?1), dropping significantly by November (6.7 Mg ha^?1, P?=?0.0027). Production of bio-oil per unit area mirrored that of harvested biomass at each harvest date; however, bio-oil yield per unit dry biomass increased from 46.6 % to 56.7 % during the season (P?=?0.0018). Allowing switchgrass to senesce lowered biomass [N] dramatically, by as much as 68 % from June to November (P?<?0.0001). Concurrently, bio-oil [N] declined from 0.51 % in June to 0.17 % by November (P?<?0.0001). Significant reductions in ash concentration were also observed in biomass and char. Finally, we show for the first time that the [N] of switchgrass biomass is a strong predictor of the [N] of bio-oil, char, and non-condensable gas with R ² values of 0.89, 0.94, and 0.88, respectively.     

Morphology and biomass production of prairie cordgrass on marginal lands

Prairie cordgrass (Spartina pectinata Link.) is indigenous throughout most of the continental United States and Canada to 60°N latitude and is well suited to marginal land too wet for maize (Zea mays L.) and switchgrass (Panicum virgatum L.). Evaluations of prairie cordgrass in Europe and North America indicated it has high potential for biomass production, relative to switchgrass, in short‐season areas. Our objective was to describe morphology and biomass production and partitioning in mature stands of ‘Red River’ prairie cordgrass and determine biomass production of natural populations on marginal land. This study was conducted from 2000 to 2008 in eastern South Dakota. Mean biomass production of mature stands of Red River was 12.7 Mg ha^?1. Leaves composed >88% of the biomass, and 60% of the tillers had no internodes. Belowground biomass to a depth of approximately 25 cm, not including roots, was 21 Mg ha^?1. Tiller density ranged from 683 tillers m^?2 for a 10‐year‐old stand to 1140 tillers m^?2 for a 4‐year‐old stand. The proaxis was composed of about eight phytomers, with rhizomes originating at proximal nodes and erect tillers at distal nodes. Vegetative propagation was achieved by both phalanx and guerilla growth. Differences among natural populations for biomass were expressed on gravelly marginal land. However, production, averaged across populations, was low (1.37 Mg ha^?1) and comparable to ‘Cave‐In‐Rock’ switchgrass (1.67 Mg ha^?1) over a 4‐year period. The large carbon storage capacity of prairie cordgrass in proaxes and rhizomes makes it useful for carbon sequestration purposes. Prairie cordgrass should be compared with switchgrass and other C₄ perennial grasses along environmental gradients to determine optimum landscape positions for each and to maximize bioenergy production and minimize inputs.     

Supply of cellulosic biomass in Illinois and implications for the Conservation Reserve Program

We developed a mathematical programming model to estimate the supply of cellulosic biomass in Illinois at various biomass prices and examine the implications of biomass production for the maintenance costs of the Conservation Reserve Program (CRP). We find that Illinois has the potential to produce about 38.4–54.5 million dry metric tons (MT) of biomass in 2020 at a biomass price of $150/MT, depending on the production costs of cellulosic feedstocks, residue collection technology, and rates of yield increases of conventional crops. Corn stover will account for more than 65% of the total biomass production across biomass prices and the scenarios considered, while the roles of wheat straw and energy crops are quite limited. Given biomass prices of $50/MT‐$150/MT, many landowners would convert their expiring CRP lands to croplands. To maintain the size of the CRP during the 2007–2020 period at the 2007 levels in Illinois, total program maintenance costs would be $104.6–176.5 million at a biomass price of $50/MT, depending on biomass production conditions and crop yields on CRP lands. This would increase to $155.2–245.4 million at a biomass price of $150/MT.     

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.     

Targeted subfield switchgrass integration could improve the farm economy,water quality,and bioenergy feedstock production

Progress on reducing nutrient loss from annual croplands has been hampered by perceived conflicts between short‐term profitability and long‐term stewardship, but these may be overcome through strategic integration of perennial crops. Perennial biomass crops like switchgrass can mitigate nitrate‐nitrogen (NO₃‐N) leaching, address bioenergy feedstock targets, and – as a lower‐cost management alternative to annual crops (i.e., corn, soybeans) – may also improve farm profitability. We analyzed publicly available environmental, agronomic, and economic data with two integrated models: a subfield agroecosystem management model, Landscape Environmental Assessment Framework (LEAF), and a process‐based biogeochemical model, DeNitrification‐DeComposition (DNDC). We constructed a factorial combination of profitability and NO₃‐N leaching thresholds and simulated targeted switchgrass integration into corn/soybean cropland in the agricultural state of Iowa, USA. For each combination, we modeled (i) area converted to switchgrass, (ii) switchgrass biomass production, and (iii) NO₃‐N leaching reduction. We spatially analyzed two scenarios: converting to switchgrass corn/soybean cropland losing >US$ 100 ha^?1 and leaching >50 kg ha^?1 (‘conservative’ scenario) or losing >US$ 0 ha^?1 and leaching >20 kg ha^?1 (‘nutrient reduction’ scenario). Compared to baseline, the ‘conservative’ scenario resulted in 12% of cropland converted to switchgrass, which produced 11 million Mg of biomass and reduced leached NO₃‐N 18% statewide. The ‘nutrient reduction’ scenario converted 37% of cropland to switchgrass, producing 34 million Mg biomass and reducing leached NO₃‐N 38% statewide. The opportunity to meet joint goals was greatest within watersheds with undulating topography and lower corn/soybean productivity. Our approach bridges the scales at which NO₃‐N loss and profitability are usually considered, and is informed by both mechanistic and empirical understanding. Though approximated, our analysis supports development of farm‐level tools that can identify locations where both farm profitability and water quality improvement can be achieved through the strategic integration of perennial vegetation.     

Perennial Grass Bioenergy Cropping on Wet Marginal Land: Impacts on Soil Properties,Soil Organic Carbon,and Biomass During Initial Establishment

The control of soil moisture, vegetation type, and prior land use on soil health parameters of perennial grass cropping systems on marginal lands is not well known. A fallow wetness-prone marginal site in New York (USA) was converted to perennial grass bioenergy feedstock production. Quadruplicate treatments were fallow control, reed canarygrass (Phalaris arundinaceae L. Bellevue) with nitrogen (N) fertilizer (75 kg N ha^?1), switchgrass (Panicum virgatum L. Shawnee), and switchgrass with N fertilizer (75 kg N ha^?1). Based on periodic soil water measurements, permanent sampling locations were assigned to various wetness groups. Surface (0–15 cm) soil organic carbon (SOC), active carbon, wet aggregate stability, pH, total nitrogen (TN), root biomass, and harvested aboveground biomass were measured annually (2011–2014). Multi-year decreases in SOC, wet aggregate stability, and pH followed plowing in 2011. For all years, wettest soils had the greatest SOC and active carbon, while driest soils had the greatest wet aggregate stability and lowest pH. In 2014, wettest soils had significantly (p?<?0.0001) greater SOC and TN than drier soils, and fallow soils had 14 to 20% greater SOC than soils of reed canarygrass + N, switchgrass, and switchgrass + N. Crop type and N fertilization did not result in significant differences in SOC, active carbon, or wet aggregate stability. Cumulative 3-year aboveground biomass yields of driest switchgrass + N soils (18.8 Mg ha^?1) were 121% greater than the three wettest switchgrass (no N) treatments. Overall, soil moisture status must be accounted for when assessing soil dynamics during feedstock establishment.