This paper develops a stochastic dynamic programming model to investigate optimal cover crop adoption policies, accounting for cumulative effects on soil fertility, uncertain future fertilizer and output prices, irreversibility of sunk machinery costs and flexibility in the timing of adoption over time. Based on data from a 35-year cotton field experiment in West Tennessee (1984–2018), we first estimate the static and dynamic yield effects of cover crop adoption and then use these estimates to evaluate the decision of a representative cotton farmer to adopt three cover cropping practices—hairy vetch, winter wheat and crimson clover—under conventional till and no-till production systems. Econometric estimates imply significant cumulative effects of cover crops on yields, as well as static and dynamic substitution effects between cover crops and nitrogen fertilizer inputs. With these substitution effects implying increasing marginal profit from soil fertility, our analysis suggests a threshold level of soil fertility level, above which it is optimal to adopt cover crops and below which it is not. Adoption of cover crops is more favored if no-till practices have been implemented. Moreover, in the presence of sunk costs that have not yet been incurred, the optimal strategy is to postpone the adoption of cover crops in both conventional till and no-till fields until crop prices improve, the cost of adoption decreases, or fertilizer prices increase. Our results also indicate that when fertilizer prices are higher, cover crop adoption in no-till systems can lead to substantial fertilizer cost savings, with the amount of those fertilizer cost savings increasing over time as soil health further improves.

Given the high level of uncertainty prevalent in the immature biofuels industry, the primary objective of this study was to identify and assess the risk factors that biofuel firms face. The study evaluated the risk factors, or specific risks, reported by biofuel firms to the U.S. Securities and Exchange Commission (SEC) over five years. The analysis was conducted for all firms in the sample, as well as for subsets of focused and diversified biofuel firms. Based on a biofuels industry risk structure derived from previous research, we coded and analyzed 4310 risk narrative disclosures, extracts from firms’ annual reports filed with the SEC. The study evaluated two risk metrics—prevalence and relevance—across 25 specific risks. Risk relevance, the most comprehensive metric, was validated by comparing it with two widely used risk metrics—which measure overall firm risk rather than specific risks—, the Z-score and the debt-to-equity ratio. Identification of risk metrics by quadrants, combined with quantile regression analysis, allowed us to identify the critical risks in the biofuels industry. The critical risks, particularly for focused biofuel firms, were biofuel regulation, biofuel markets, feedstock markets, conversion technologies, profitable operations, financing, and risk management. To a lesser extent, environmental and contracting risks were critical. The results of this study can guide policymakers and firm managers in developing a compelling policy mix and strategies to address the challenges faced by the biofuels industry.

Abstract Lake water level fluctuations are an important factor driving variation in many ecosystem processes. The nearshore sediments that are periodically exposed and re‐inundated can develop distinct physical and chemical characteristics, especially in relationship to the organic matter content of the sediments and the particle size distribution. These sediment characteristics in turn can alter the flux of nitrogen (N) and phosphorus (P) from sediments into the water column when sediments are inundated. Here, we used intact sediment core experiments across a range of sediment inundation frequencies to estimate the effect of inundation frequency on sediment nutrient flux in Kabetogama Lake, Minnesota, USA. We observed associations between elevation or inundation frequency and some sediment characteristics, but in a structural equation model, inundation frequency and the sediment properties we measured were poorly related to inorganic nutrient flux. On the other hand, inundation frequency did have a moderate association with organic N and P flux from sediments, which could be due to decay of terrestrial organic matter that accumulates on exposed sediments. We used our parameterized structural equation model to estimate how three different water level management regimes employed over the past 50 years could influence organic N and P flux from sediments. The models suggested more recent water level management regimes reduced organic N and P flux by 9%–13% and 5.9%–9.8%, respectively. Nearshore sediment flux could sustain and influence harmful algal blooms that occur in this lake, and these fluxes could be influenced by water level management.

From 1900 to 1932 a copper (Cu) mill operated near Gay, Michigan, along the eastern shore of the Keweenaw Peninsula (Lake Superior, Michigan) and discharged waste material (stamp sands [SS]) to a nearby beach. These SS escaped containment structures and have been redeposited by wave action along the beaches in northern Grand Traverse Bay and onto Buffalo Reef, an important spawning area for native fish. Newly hatched fish move into nearby beach habitats where they grow during their first summer. Juvenile fish initially consume zooplankton before switching to benthic invertebrates once they are large enough. SS contain metals (especially Cu) that are toxic to many invertebrate taxa, and studies have observed few benthic taxa in areas covered by SS. We sampled the invertebrate community from four Lake Whitefish nursery areas: one near Buffalo Reef with high SS, one south of the Traverse River with moderate SS, one in nearby Little Traverse Bay with little SS, and a beach ∼58 km away with no SS (Big Bay). We also resampled the benthos at sites that had been sampled as part of an earlier Grand Traverse Bay study. Buffalo Reef (high SS) had fewer benthic taxa, and less density of several taxa than Little Traverse Bay (little SS), especially benthic copepods. All beaches had comparable zooplankton diversity, but the abundance was ∼2 orders of magnitude lower at Buffalo Reef (high SS) than other beaches. Cu and several other metals were elevated at beaches with more SS. We found support for associations between benthic density and diversity with depth (positive effect) and Cu concentration (negative effect). Cu concentration was a better predictor of declines in benthic invertebrate abundance and diversity than SS. We also observed that the relationship between Cu concentration and SS was non-linear, and highly variable. For example, 149 mg Cu/kg dry weight sediment is a consensus toxicity threshold used in the literature, but the prediction interval around that concentration from our model is 26-851 mg Cu/kg dry weight. A better predictive model of this relationship would be beneficial to develop to understand what level of SS reduction would prevent Cu impacts on invertebrates.### Competing Interest StatementThe authors have declared no competing interest.

Woody biomass feedstock processing, including sorting, drying, and size reduction of biomass to provide standardized reactor-ready biomass to the biorefinery, is crucial to biofuel conversion. This study compares two comminution technology systems applied to woody biomass processing at a depot before being utilized for biofuel production at a biorefinery. The conventional comminution technology, known as the hammermill system, is compared with a rotary shear system developed by Forest Concepts™. Potential economic savings of using the new technology are evaluated by applying a deterministic and a stochastic partial capital budgeting model based on results from an experiment that processed chipped hybrid poplar chips and forest residues with both systems. The stochastic partial capital model estimates that savings will vary between approximately USD 28 and USD 42 per ton of reactor-ready processed biomass, with mean and median values around USD 34 per ton. It is 90% likely that savings will be between USD 30 and USD 39 per ton of reactor-ready processed biomass. The estimated savings are mainly due to differences in input (feedstock) to output (reactor-ready biomass) yields between technologies, affecting feedstock and drying costs.

In large lakes, metal availability sometimes limits the acquisition of nutrients (nitrogen, N and phosphorus, P) in offshore waters that are relatively isolated from tributaries and sediments. We hypothesize that metals may also be important within harmful algal blooms (HABs). HABs occur where nutrient loads are elevated, but bioassays often indicate that phytoplankton in HABs are N or P limited. Nutrient limitation may be exacerbated by corresponding limitations in several metals (i.e. nickel - Ni, molybdenum - Mo, zinc - Zn, and iron - Fe) that facilitate uptake and transformation of oxidized and organic forms of nutrients, such as urea, nitrate and organic phosphorus. The cyanotoxin microcystin has been hypothesized to have a role in metal management, so metal demand may also influence the toxicity of HABs. Here, we used nutrient diffusing substrates to measure how N, P, Ni, Mo, Zn and Fe amendments influenced the growth and toxicity of periphyton. Periphyton was grown suspended in 10 nearshore sites in Lake Michigan and Lake Erie (5 with and 5 without perennial HABs). Outside of blooms, we found no evidence for metal limitation or co-limitation. However, evidence for metal co-limitation was observed in two HABs sites (Zn in Green Bay and Zn, Mo, Ni and Fe in Sandusky Bay). N, P and Zn amendments all stimulated microcystin content in Maumee Bay. These data indicate that nutrient limitation occurs even within blooms, and the availability of metals may have an influence on growth, community composition and toxicity.

Efforts to reduce the frequency, extent, and toxicity of harmful algal blooms (HABs) require knowledge about drivers of algal growth, toxin production, and shifts in phytoplankton community composition to cyanobacterial dominance. Although labile nitrogen (N) and phosphorus (P) fuel primary production, micronutrients also play roles as the enzymatic engines that facilitate rapid and efficient growth and toxin production. Macro- and micronutrient availability can shape community composition and function by selecting for particular taxa. To address how phytoplankton in two Great Lakes subbasins respond to macro- and micronutrients, we conducted bottle incubation enrichment experiments using water collected from two blooming and two nonblooming sites in Lakes Erie and Michigan during late summer (August). Three of the four sites exhibited multi-nutrient limitation of growth. Both blooming sites responded strongest to NH 4 + enrichment. Both nonblooming sites responded the strongest to PO 4 3 - enrichment, and three of the four sites responded in some way to a mix of micronutrients (Fe, Mn, Mo, Ni, and Zn). Microcystis aeruginosa relative abundance increased most with N enrichment, while P enrichment increased the abundance of diatoms and chlorophytes. At the Fox River, N-enriched communities grew 10%-20% more than non-N enriched communities (measured as chlorophyll a), and N-enriched communities had, on average, over twice as much microcystin (non-N communities average MC = 2.45 μg · L-1, +N communities MC = 5.35 μg · L-1). These overarching trends support the idea that control of HABs may not be effective with a P-only approach.

Forest residues have been suggested as potential feedstock for sustainable aviation fuel (SAF) production through different pathways. However, the bulky density and scatter distribution require efficient size-reduction processes to enhance the feedstock supply. Thus, this study analyzes the impact of alternative preprocessing and conversion technologies on the SAF supply chains from logging residues (the predominant share of forest residues) using a two-stage mixed-integer linear programming model. The model determines the optimal location of biomass preprocessing depots, conversion facilities, and airports receiving SAF by minimizing the net present value of the total supply chain cost over 10 years. Using high-resolution spatial data in the Southeast U.S.A. as a case study, the results show that the technology and scale of the facilities heavily influenced the SAF's breakeven cost and maximum supply quantity. The most economically efficient system that adopts a rotary shear milling system and pyrolysis conversion process could generate up to 650 million gallons of SAF from logging residues in the region, with nearly 62% of the SAF being produced from hardwood residues. Also, the most efficient system has an estimated breakeven cost of US$5.51 per gallon of SAF.

AbstractWatershed nutrient management often focuses on actions that reduce the movement of nitrogen (N) and phosphorus (P) from agricultural lands into streams. One area of management focus is the buffer of land adjacent to streams. Wetlands and forests in this buffer can intercept and retain N and P from the landscape. In addition to directly intercepting agricultural nutrients, natural habitats in the buffer can alter stream geomorphology and influence the in‐stream processing and transformation of N and P to less labile and mobile forms. Here, we assess the influence of buffer land cover on in‐stream processing of N and P. We measured nutrient dynamics in the water column and sediments of agricultural streams in the Fox River and Duck Creek watersheds (WI, USA) during the growing season. In these streams, water column processing was low, possibly due to a lack of primary producers in the water column. Water column P processing was weakly associated with wetland land cover in the buffer, but buffer land cover had no clear effect on inorganic N processing. On the other hand, sediments were almost always a source of inorganic P and a sink for inorganic N. Sediment P release was higher in streams with more agricultural land cover in the buffer. Sediments in streams with agricultural land cover in the buffer also removed more nitrate, even after accounting for the greater availability of nitrate in those streams. The buffer land cover conditions we quantified occupy a very small portion of the overall watershed (100 m wide, for 1 km upstream of the study site) but nevertheless appear to influence in‐stream cycling of N and P. For P management, reducing agricultural land cover in buffers is already a priority due to the ability of wetlands and forests to intercept nutrients, but this study suggests there may be some additional benefit due to changes in in‐stream P processing.

This study designs and evaluates the economics and spatial configuration of a supply chain for sustainable aviation fuel from hybrid poplar in the southeast US region. Mixed integer linear programming is used to satisfy a hypothetical demand of 120 Mgal year-1 for two production systems, one using conventional preprocessing technology (the hammermill system) and the other using a newly introduced technology (the rotary shear system). The economic impact of these preprocessing technologies is evaluated across all supply chain stages, as well as the vehicle mileage traveled. Results suggest that the rotary shear system presents some economic advantages over the hammermill system. Compared to the traditional system, the rotary shear system decreases preprocessing costs by 6.4%, reactor-ready biomass costs by 15.2%, and sustainable aviation fuel production costs by 7.9%. The rotary shear system also requires 25.2% less planted area of hybrid poplar than the hammermill system, thus reducing the vehicle mileage traveled along the supply chain, which has positive implications for emissions and vehicle risk exposure.

Abstract Winter oilseed Brassica plants have several documented allelochemicals; however, most literature revolves around the application of seed meal to fields, or the use of aerial parts of the plant. It is not clear if these chemicals interact with the surrounding environment to the same extent if the winter oilseeds are harvested as a cash crop in the spring. To determine this, we conducted a preliminary study bioassay using water extractable compounds from canola (Brassica napus L.) and pennycress (Thlaspi arvense L.) roots diluted to 25 and 50% (v/v). These four extracts, as well as deionized water for control, were used to irrigate plates with the seeds of soybean (Glycine max L.), Palmer amaranth [Amaranthus palmeri (S.) Watson], and mare's tail (Erigeron canadensis). We measured germination percent per plate and seedling radicle and hypocotyl lengths after 8 days of treatment. Mare's tail germination was lowered by 40% on day 4 by 50% pennycress extracts, and root length was stunted by both canola and pennycress extracts by 3–5 mm. Palmer amaranth root length was stunted by 10–15 mm by both species’ extracts, as well as shoots lengthened by 5–10 mm. Extract treatments did not affect soybean germination or growth. These interactions indicate potential for allelopathic interactions in the field following harvest of dual cropped winter oilseed and herbicide‐resistant weeds and warrant further study into the topic.

Winter oilseeds are cool season Brassica crops currently being grown in the upper Midwest and North-West of the United States. They have the potential to function as dual crops when grown in rotation with corn, soybean, and small grains. They provide many of the benefits of typical cover crops over winter, with the added benefit of extra revenue to growers who sell the seeds for uses such as biofuel, industrial products, human consumption, or animal feed. This review gathers current agronomic and industrial use information about canola (Brassica napus L.), camelina [Camelina sativa (L.) Crantz], and pennycress (Thlaspi arvense L.). Currently, most research involving these crops is specific to the Midwest. This review also poses questions regarding how these crops could be adapted to grow in the Mid-South, with further research being necessary in several areas before promoting adoption in the region.

Crop rotations, cover crops, and poultry litter (PL) under no tillage (NT) may improve soil health and crop yields. However, farmers' adoption depends on whether they can generate extra profits. This study evaluated profitability of NT corn (Zea mays L.) in monoculture versus rotations with soybean (Glycine max L.) and cotton (Gossypium hirsutum L.) with or without winter covers from 2002 to 2017. Whole-block treatments were cropping rotations with monoculture (control) versus nine, 4-yr cropping sequences (phases) repeated four times (I, II, III, and IV). Split-block treatments were no cover versus winter covers of PL, hairy vetch (Vicia villosa L.), and wheat (Triticum aestivum L.). Different phases influenced yields and net returns (NRs; p < .05), with the greatest NRs in Phase IV, and the lowest in Phase III. Rotation interacted with phase to influence corn yield and NRs (p < .01), with positive rotation effects occurring in Phase IV. Covers influenced yields and NRs over 16 yr (p < .01). Vetch cover resulted in the highest corn yields, whereas wheat cover was the lowest. However, no cover plots produced NRs greater than any other cover. Enhanced yields or cost savings due to reduced fertilizer from covers did not offset cover costs. Lowering costs of PL, hairy vetch, and wheat by 70, 68, and 100%, respectively, from their base values produced equivalent NRs to no cover. Thus, farmers may need subsidies to adopt conservation agriculture-based practices.

Abstract Water level (WL) fluctuations substantially alter the fauna, flora, and microbial community of nearshore aquatic ecosystems. Water level management therefore has the potential to strongly influence a wide variety of ecosystem processes. Many northern temperate lake food webs experience substantial methylmercury contamination, which is partially mediated by the action of sulfate‐reducing bacteria occurring in sediments that are periodically inundated. For lakes with elevated methylmercury, WL management could be designed to reduce methylmercury contamination. At the lake scale, this concept is supported by studies that identified statistical associations between fish mercury content and water level (WL) fluctuations. Here, we compiled a long‐term dataset (1997–2015) of mercury content in young‐of‐year Yellow Perch (Perca flavescens) from six lakes on the border of the United States and Canada and examined whether mercury content was associated with WL fluctuation. Many WL metrics covary and appear to have strong associations with Yellow Perch mercury. However, these associations appear to vary by lake, and lake‐specific models are needed to identify relationships between WL fluctuation and Yellow Perch mercury content. We used partial least‐squares regression (PLSR) to identify the associations between Yellow Perch mercury content and WL metrics, temperature, and annual deposition data for lakes in northern Minnesota. These PLSR models not only showed some variation among lakes, but also supported strong associations between WL fluctuations and annual variation in Yellow Perch mercury content. The study lakes underwent a change in WL management in 2000, when winter WL minimums were increased by about 1 m in five of the six study lakes, which reduced annual WL fluctuation on those lakes. Using the PLSR models, we estimated how this change in WL management would have affected Yellow Perch mercury content. In four of the five study lakes in which annual WL fluctuation was reduced in 2000, the change in WL management likely reduced Yellow Perch mercury content, relative to the previous WL management regime.

This chapter introduces an integrative framework coupling GIS tools, biophysical model, enterprise budgeting tools, GHG emission models, and optimization mechanism in determining a sustainable switchgrass biofuel supply chain network. The integrative framework is applied to a case study of replacing 30% of gasoline used in transportation in Tennessee. Using high-resolution spatial data in a multiobjective mixed-integer programming model, we find that land use choice makes substantial impacts on the deployment of the supply chains under different objectives. When considering private cost alone, hay and pasture land concentrated in the east and central Tennessee will be the major source for switchgrass production. If targeting GHG emission minimization solely, more than 500 thousand hectares of the state’s cropland is converted to switchgrass for biofuel production. Moreover, the trade-off between cost and GHG emissions in the supply chains shows that the marginal rate of substitution between total cost and GHG emissions on the frontier curve increases at an accelerating rate. Our findings illustrate the importance of land resource management on the sustainability of a dedicated energy crop supply chain.

Crop rotations, cover crops, and manures may enhance yields, improve soils, and provide other ecosystem services. However, farmers may be reluctant to adopt the aforementioned practices because of uncertain profits. This study determined the profitability of cotton (Gossypium hirsutum L.) rotated with other crops and also utilizing cover crops and poultry litter (PL). Whole-block treatments were 10 sequences of no-tillage cotton, corn (Zea mays L.), and soybean [Glycine max (L.) Merr.] at Milan, TN. Sequences were repeated in 4-yr cycles called Phases (Phases I, II, III, and IV) starting in 2002 and continuing through 2017 to assess effects of consecutive applications of sequences on cotton net returns (NRs). Split-block treatments included winter wheat (Triticum aestivum L.), hairy vetch (Vicia villosa L.), PL, and fallow. The ANOVA was used to determine treatment NR differences compared to continuous cotton and fallow for 2002-2017 and for each Phase. Including soybean and corn in rotation with cotton did not positively affect cotton NRs in Phases I, II, and III. Droughts may explain lack of yield and NR response in Phases II and III. However, including soybean and corn in the rotation provided higher cotton NRs in Phase IV (2014-2017). Better weather and improved soils with residue diversity in Phase IV may explain higher yields and NRs of cotton in rotation with other crops. For cover crops and PL, yield benefits and/or N fertilizer savings did not offset input costs, indicating monetary incentives may be needed for famers to include these practices in their cropping system.

This study evaluated the economic feasibility of fast pyrolysis biorefineries fed with blended pine residues and switchgrass in the Southeastern U.S. with different supply chain design. Previous techno-economic analyses (TEA) have focused on either blended biomass or decentralized preprocessing without investigating the impacts of varied process parameters, technology options, and real-world biomass distribution. This study fills the literature gap by modeling scenarios for different biomass blending ratios, biorefinery and preprocessing site (so-called depot) capacities, and alternative preprocessing technologies. High-resolution, real-world geospatial data were analyzed using Geographic Information Systems to facilitate supply chain design and TEA. For a decentralized system, the minimum fuel selling price (MFSP) of biofuel was $3.92–$4.33 per gallon gasoline equivalent (GGE), while the MFSP for the centralized biorefinery at the same capacities ranged between $3.75–$4.02/GGE. Implementing a high moisture pelleting process depot rather than a conventional pelleting process lowered the MFSP by $0.03–$0.17/GGE. Scenario analysis indicated decreased MFSP with increasing biorefinery capacities but not necessarily with increasing depot size. Medium-size depots (500 OMDT/day) achieved the lowest MFSP. This analysis identified the optimal blending ratios for two preprocessing technologies at varied depot sizes. Counterintuitively, increasing the proportion of higher cost switchgrass reduced the MFSP for large biorefineries (>5000 ODMT/day), but increased the MFSP for small biorefineries (1000–2500 ODMT/day). Although the decentralized systems have a higher MFSP based on current analysis, it has other potential benefits such as mitigated supply chain risks and improved feedstock quality that are difficult to be quantified in this TEA.

Pennycress can be used as a renewable biomass because its harvested seeds can be converted into biofuel, supplying, for example the aviation industry. Pennycress can be adopted as a winter cover crop to make extra profit in addition to summer cash crops. This study ascertains influences on row crop farmers' interest in growing pennycress to supply a biofuels industry. The study uses data from a survey of row-crop farmers in seven US states. Effects of farm and farmer attributes on acceptance of a farmgate pennycress price are measured. Nearly 58% were interested in growing pennycress if profitable. Among those interested, 54.4% would accept the farmgate pennycress price offered. Positive influences on interest included farm size, education, and familiarity with pennycress, while concern about knowledge on growing pennycress, and use of no-till practices had negative influences. Farmers aged 40 to 65 were more likely to accept the price, while share of rented hectares and no debt had positive influences. More risk-averse farmers and those using no-till were less likely to accept. Results suggest that the majority of row crop farmers would be interested in growing pennycress if profitable, while the overall willingness to accept the farmgate price was when it was at $0.28/kg.