Hydrological responses of land use change from cotton (Gossypium hirsutum L.) to cellulosic bioenergy crops in the Southern High Plains of Texas,USA

The Southern High Plains (SHP) region of Texas in the United States, where cotton is grown in a vast acreage, has the potential to grow cellulosic bioenergy crops such as perennial grasses and biomass sorghum (Sorghum bicolor). Evaluation of hydrological responses and biofuel production potential of hypothetical land use change from cotton (Gossypium hirsutum L.) to cellulosic bioenergy crops enables better understanding of the associated key agroecosystem processes and provides for the feasibility assessment of the targeted land use change in the SHP. The Soil and Water Assessment Tool (SWAT) was used to assess the impacts of replacing cotton with perennial Alamo switchgrass (Panicum virgatum L.), Miscanthus × giganteus (Miscanthus sinensis Anderss. [Poaceae]), big bluestem (Andropogon gerardii) and annual biomass sorghum on water balances, water use efficiency and biofuel production potential in the Double Mountain Fork Brazos watershed. Under perennial grass scenarios, the average (1994–2009) annual surface runoff from the entire watershed decreased by 6–8% relative to the baseline cotton scenario. In contrast, surface runoff increased by about 5% under the biomass sorghum scenario. Perennial grass land use change scenarios suggested an increase in average annual percolation within a range of 3–22% and maintenance of a higher soil water content during August to April compared to the baseline cotton scenario. About 19.1, 11.1, 3.2 and 8.8 Mg ha^?1 of biomass could potentially be produced if cotton area in the watershed would hypothetically be replaced by Miscanthus, switchgrass, big bluestem and biomass sorghum, respectively. Finally, Miscanthus and switchgrass were found to be ideal bioenergy crops for the dryland and irrigated systems, respectively, in the study watershed due to their higher water use efficiency, better water conservation effects, greater biomass and biofuel production potential, and minimum crop management requirements.     

Assessing the hydrologic and water quality impacts of biofuel‐induced changes in land use and management

The Southern High Plains (SHP) of Texas, where cotton (Gossypium hirsutum L.) is grown in vast acreage, and the Texas Rolling Plains (TRP), which is dominated by an invasive brush, honey mesquite (Prosopis glandulosa) have the potential for biofuel production for meeting the U.S. bioenergy target of 2022. However, a shift in land use from cotton to perennial grasses and a change in land management such as the harvesting of mesquite for biofuel production can significantly affect regional hydrology and water quality. In this study, APEX and SWAT models were integrated to assess the impacts of replacing cotton with Alamo switchgrass (Panicum virgatum L.) and Miscanthus × giganteus in the upstream subwatershed and harvesting mesquite in the downstream subwatershed on water and nitrogen balances in the Double Mountain Fork Brazos watershed in the SHP and TRP regions. Simulated average (1994–2009) annual surface runoff from the baseline cotton areas decreased significantly (P < 0.05) by 88%, and percolation increased by 28% under the perennial grasses scenario compared to the baseline cotton scenario. The soil water content enhanced significantly under the irrigated switchgrass scenario compared to the baseline irrigated cotton scenario from January to April and August to October. However, the soil water content was depleted significantly under the dryland Miscanthus scenario from April to July relative to the baseline dryland cotton scenario. The nitrate‐nitrogen (NO₃‐N) and organic‐N loads in surface runoff and NO₃‐N leaching to groundwater reduced significantly by 86%, 98%, and 100%, respectively, under the perennial grasses scenario. Similarly, surface runoff, and NO₃‐N and organic‐N loads through surface runoff reduced significantly by 98.9%, 99.9%, and 99.5%, respectively, under the post‐mesquite‐harvest scenario. Perennial grasses exhibited superior ethanol production potential compared to mesquite. However, mesquite is an appropriate supplementary bioenergy source in the TRP region because of its standing biomass and rapid regrowth characteristics.     

Impact of agronomic uncertainty in biomass production and endogenous commodity prices on cellulosic biofuel feedstock composition

This study evaluates the effect of agronomic uncertainty on bioenergy crop production as well as endogenous commodity and biomass prices on the feedstock composition of cellulosic biofuels under a binding mandate in the United States. The county‐level simulation model focuses on both field crops (corn, soybean, and wheat) and biomass feedstocks (corn stover, wheat straw, switchgrass, and Miscanthus). In addition, pasture serves as a potential area for bioenergy crop production. The economic model is calibrated to 2022 in terms of yield, crop demand, and baseline prices and allocates land optimally among the alternative crops given the binding cellulosic biofuel mandate. The simulation scenarios differ in terms of bioenergy crop type (switchgrass and Miscanthus) and yield, biomass production inputs, and pasture availability. The cellulosic biofuel mandates range from 15 to 60 billion L. The results indicate that the 15 and 30 billion L mandates in the high production input scenarios for switchgrass and Miscanthus are covered entirely by agricultural residues. With the exception of the low production input for Miscanthus scenario, the share of agricultural residues is always over 50% for all other scenarios including the 60 billion L mandate. The largest proportion of agricultural land dedicated to either switchgrass or Miscanthus is found in the southern Plains and the southeast. Almost no bioenergy crops are grown in the Midwest across all scenarios. Changes in the prices for the three commodities are negligible for cellulosic ethanol mandates because most of the mandate is met with agricultural residues. The lessons learned are that (1) the share of agricultural residue in the feedstock mix is higher than previously estimated and (2) for a given mandate, the feedstock composition is relatively stable with the exception of one scenario.     

Crassulacean acid metabolism (CAM) offers sustainable bioenergy production and resilience to climate change

Biomass production on low‐grade land is needed to meet future energy demands and minimize resource conflicts. This, however, requires improvements in plant water‐use efficiency (WUE) that are beyond conventional C3 and C4 dedicated bioenergy crops. Here we present the first global‐scale geographic information system (GIS)‐based productivity model of two highly water‐efficient crassulacean acid metabolism (CAM) candidates: Agave tequilana and Opuntia ficus‐indica. Features of these plants that translate to WUE advantages over C3 and C4 bioenergy crops include nocturnal stomatal opening, rapid rectifier‐like root hydraulic conductivity responses to fluctuating soil water potential and the capacity to buffer against periods of drought. Yield simulations for the year 2070 were performed under the four representative concentration pathway (RCPs) scenarios presented in the IPCC's 5th Assessment Report. Simulations on low‐grade land suggest that O. ficus‐indica alone has the capacity to meet ‘extreme’ bioenergy demand scenarios (>600 EJ yr^?1) and is highly resilient to climate change (?1%). Agave tequilana is moderately impacted (?11%). These results are significant because bioenergy demand scenarios >600 EJ yr^?1 could be met without significantly increasing conflicts with food production and contributing to deforestation. Both CAM candidates outperformed the C4 bioenergy crop, Panicum virgatum L. (switchgrass) in arid zones in the latitudinal range 30°S–30°N.     

Soil & Water Assessment Tool (SWAT) simulated hydrological impacts of land use change from temperate grassland to energy crops: A case study in western UK

When considering the large‐scale deployment of bioenergy crops, it is important to understand the implication for ecosystem hydrological processes and the influences of crop type and location. Based on the potential for future land use change (LUC), the 10,280 km² West Wales Water Framework Directive River Basin District (UK) was selected as a typical grassland dominated district, and the Soil & Water Assessment Tool (SWAT) hydrology model with a geographic information systems interface was used to investigate implications for different bioenergy deployment scenarios. The study area was delineated into 855 sub‐basins and 7,108 hydrological response units based on rivers, soil type, land use, and slope. Changes in hydrological components for two bioenergy crops (Miscanthus and short rotation coppice, SRC) planted on 50% (2,192 km²) or 25% (1,096 km²) of existing improved pasture are quantified. Across the study area as a whole, only surface run‐off with SRC planted at the 50% level was significantly impacted, where it was reduced by up to 23% (during April). However, results varied spatially and a comparison of annual means for each sub‐basin and scenario revealed surface run‐off was significantly decreased and baseflow significantly increased (by a maximum of 40%) with both Miscanthus and SRC. Evapotranspiration was significantly increased with SRC (at both planting levels) and water yield was significantly reduced with SRC (at the 50% level) by up to 5%. Effects on streamflow were limited, varying between ?5% and +5% change (compared to baseline) in the majority of sub‐basins. The results suggest that for mesic temperate grasslands, adverse effects from the drying of soil and alterations to streamflow may not arise, and with surface run‐off reduced and baseflow increased, there could, depending on crop location, be potential benefits for flood and erosion mitigation.     

Investment risk in bioenergy crops

Perennial, cellulosic bioenergy crops represent a risky investment. The potential for adoption of these crops depends not only on mean net returns, but also on the associated probability distributions and on the risk preferences of farmers. Using 6‐year observed crop yield data from highly productive and marginally productive sites in the southern Great Lakes region and assuming risk neutrality, we calculate expected breakeven biomass yields and prices compared to corn (Zea mays L.) as a benchmark. Next we develop Monte Carlo budget simulations based on stochastic crop prices and yields. The crop yield simulations decompose yield risk into three components: crop establishment survival, time to maturity, and mature yield variability. Results reveal that corn with harvest of grain and 38% of stover (as cellulosic bioenergy feedstock) is both the most profitable and the least risky investment option. It dominates all perennial systems considered across a wide range of farmer risk preferences. Although not currently attractive for profit‐oriented farmers who are risk neutral or risk averse, perennial bioenergy crops have a higher potential to successfully compete with corn under marginal crop production conditions.     

Cover crop root contributions to soil carbon in a no‐till corn bioenergy cropping system

Crop residues are potential biofuel feedstocks, but residue removal may reduce soil carbon (C). The inclusion of a cover crop in a corn bioenergy system could provide additional biomass, mitigating the negative effects of residue removal by adding to stable soil C pools. In a no‐till continuous corn bioenergy system in the northern US Corn Belt, we used ¹³CO₂ pulse labeling to trace plant C from a winter rye (Secale cereale) cover crop into different soil C pools for 2 years following rye cover crop termination. Corn stover left as residue (30% of total stover) contributed 66, corn roots 57, rye shoots 61, rye roots 50, and rye rhizodeposits 25 g C m^?2 to soil. Five months following cover crop termination, belowground cover crop inputs were three times more likely to remain in soil C pools than were aboveground inputs, and much of the root‐derived C was in mineral‐associated soil fractions. After 2 years, both above‐ and belowground inputs had declined substantially, indicating that the majority of both root and shoot inputs are eventually mineralized. Our results underscore the importance of cover crop roots vs. shoots and the importance of cover crop rhizodeposition (33% of total belowground cover crop C inputs) as a source of soil C. However, the eventual loss of most cover crop C from these soils indicates that cover crops will likely need to be included every year in rotations to accumulate soil C.     

Perennial rhizomatous grasses as bioenergy feedstock in SWAT: parameter development and model improvement

The Soil and Water Assessment Tool (SWAT) is increasingly used to quantify h y drologic and water quality impacts of bioenergy production, but crop‐growth parameters for candidate perennial rhizomatous grasses (PRG) Miscanthus × giganteus and upland ecotypes of Panicum virgatum (switchgrass) are limited by the availability of field data. Crop‐growth parameter ranges and suggested values were developed in this study using agronomic and weather data collected at the Purdue University Water Quality Field Station in northwestern Indiana. During the process of parameterization, the comparison of measured data with conceptual representation of PRG growth in the model led to three changes in the SWAT 2009 code: the harvest algorithm was modified to maintain belowground biomass over winter, plant respiration was extended via modified‐DLAI to better reflect maturity and leaf senescence, and nutrient uptake algorithms were revised to respond to temperature, water, and nutrient stress. Parameter values and changes to the model resulted in simulated biomass yield and leaf area index consistent with reported values for the region. Code changes in the SWAT model improved nutrient storage during dormancy period and nitrogen and phosphorus uptake by both switchgrass and Miscanthus.     

Land‐use legacies regulate decomposition dynamics following bioenergy crop conversion

Land‐use conversion into bioenergy crop production can alter litter decomposition processes tightly coupled to soil carbon and nutrient dynamics. Yet, litter decomposition has been poorly described in bioenergy production systems, especially following land‐use conversion. Predicting decomposition dynamics in postconversion bioenergy production systems is challenging because of the combined influence of land‐use legacies with current management and litter quality. To evaluate how land‐use legacies interact with current bioenergy crop management to influence litter decomposition in different litter types, we conducted a landscape‐scale litterbag decomposition experiment. We proposed land‐use legacies regulate decomposition, but their effects are weakened under higher quality litter and when current land use intensifies ecosystem disturbance relative to prior land use. We compared sites left in historical land uses of either agriculture (AG) or Conservation Reserve Program grassland (CRP) to those that were converted to corn or switchgrass bioenergy crop production. Enzyme activities, mass loss, microbial biomass, and changes in litter chemistry were monitored in corn stover and switchgrass litter over 485 days, accompanied by similar soil measurements. Across all measured variables, legacy had the strongest effect (P < 0.05) relative to litter type and current management, where CRP sites maintained higher soil and litter enzyme activities and microbial biomass relative to AG sites. Decomposition responses to conversion depended on legacy but also current management and litter type. Within the CRP sites, conversion into corn increased litter enzymes, microbial biomass, and litter protein and lipid abundances, especially on decomposing corn litter, relative to nonconverted CRP. However, conversion into switchgrass from CRP, a moderate disturbance, often had no effect on switchgrass litter decomposition parameters. Thus, legacies shape the direction and magnitude of decomposition responses to bioenergy crop conversion and therefore should be considered a key influence on litter and soil C cycling under bioenergy crop management.     

Initial soil C and land‐use history determine soil C sequestration under perennial bioenergy crops

In the UK and other temperate regions, short rotation coppice (SRC) and Miscanthus x giganteus (Miscanthus) are two of the leading ‘second‐generation’ bioenergy crops. Grown specifically as a low‐carbon (C) fossil fuel replacement, calculations of the climate mitigation provided by these bioenergy crops rely on accurate data. There are concerns that uncertainty about impacts on soil C stocks of transitions from current agricultural land use to these bioenergy crops could lead to either an under‐ or overestimate of their climate mitigation potential. Here, for locations across mainland Great Britain (GB), a paired‐site approach and a combination of 30‐cm‐ and 1‐m‐deep soil sampling were used to quantify impacts of bioenergy land‐use transitions on soil C stocks in 41 commercial land‐use transitions; 12 arable to SRC, 9 grasslands to SRC, 11 arable to Miscanthus and 9 grasslands to Miscanthus. Mean soil C stocks were lower under both bioenergy crops than under the grassland controls but only significant at 0–30 cm. Mean soil C stocks at 0–30 cm were 33.55 ± 7.52 Mg C ha^?1 and 26.83 ± 8.08 Mg C ha^?1 lower under SRC (P = 0.004) and Miscanthus plantations (P = 0.001), respectively. Differences between bioenergy crops and arable controls were not significant in either the 30‐cm or 1‐m soil cores and smaller than for transitions from grassland. No correlation was detected between change in soil C stock and bioenergy crop age (time since establishment) or soil texture. Change in soil C stock was, however, negatively correlated with the soil C stock in the original land use. We suggest, therefore, that selection of sites for bioenergy crop establishment with lower soil C stocks, most often under arable land use, is the most likely to result in increased soil C stocks.     

Potential impacts on ecosystem services of land use transitions to second‐generation bioenergy crops in GB

We present the first assessment of the impact of land use change (LUC) to second‐generation (2G) bioenergy crops on ecosystem services (ES) resolved spatially for Great Britain (GB). A systematic approach was used to assess available evidence on the impacts of LUC from arable, semi‐improved grassland or woodland/forest, to 2G bioenergy crops, for which a quantitative ‘threat matrix’ was developed. The threat matrix was used to estimate potential impacts of transitions to either Miscanthus, short‐rotation coppice (SRC, willow and poplar) or short‐rotation forestry (SRF). The ES effects were found to be largely dependent on previous land uses rather than the choice of 2G crop when assessing the technical potential of available biomass with a transition from arable crops resulting in the most positive effect on ES. Combining these data with constraint masks and available land for SRC and Miscanthus (SRF omitted from this stage due to lack of data), south‐west and north‐west England were identified as areas where Miscanthus and SRC could be grown, respectively, with favourable combinations of economic viability, carbon sequestration, high yield and positive ES benefits. This study also suggests that not all prospective planting of Miscanthus and SRC can be allocated to agricultural land class (ALC) ALC 3 and ALC 4 and suitable areas of ALC 5 are only minimally available. Beneficial impacts were found on 146 583 and 71 890 ha when planting Miscanthus or SRC, respectively, under baseline planting conditions rising to 293 247 and 91 318 ha, respectively, under 2020 planting scenarios. The results provide an insight into the interplay between land availability, original land uses, bioenergy crop type and yield in determining overall positive or negative impacts of bioenergy cropping on ecosystems services and go some way towards developing a framework for quantifying wider ES impacts of this important LUC.     

21st‐century biogeochemical modeling: Challenges for Century‐based models and where do we go from here?

21st‐century modeling of greenhouse gas (GHG) emissions from bioenergy crops is necessary to quantify the extent to which bioenergy production can mitigate climate change. For over 30 years, the Century‐based biogeochemical models have provided the preeminent framework for belowground carbon and nitrogen cycling in ecosystem and earth system models. While monthly Century and the daily time‐step version of Century (DayCent) have advanced our ability to predict the sustainability of bioenergy crop production, new advances in feedstock generation, and our empirical understanding of sources and sinks of GHGs in soils call for a re‐visitation of DayCent's core model structures. Here, we evaluate current challenges with modeling soil carbon dynamics, trace gas fluxes, and drought and age‐related impacts on bioenergy crop productivity. We propose coupling a microbial process‐based soil organic carbon and nitrogen model with DayCent to improve soil carbon dynamics. We describe recent improvements to DayCent for simulating unique plant structural and physiological attributes of perennial bioenergy grasses. Finally, we propose a method for using machine learning to identify key parameters for simulating N₂O emissions. Our efforts are focused on meeting the needs for modeling bioenergy crops; however, many updates reviewed and suggested to DayCent will be broadly applicable to other systems.     

Valuation of ecosystem services in alternative bioenergy landscape scenarios

Agricultural land in the Midwest is a source of food and fuel, as well as biodiversity. It is also a cause of excess nutrients that make their way to the Mississippi River and the Gulf of Mexico. To address unsustainable changes to biogeochemical cycles and ecosystem functions, a multidisciplinary approach involving social science, natural science, and engineering is often effective. Given the potential of second‐generation biofuels, and capitalizing on the deep‐rooted perennial bioenergy crops capable of thriving in poor soils, we demonstrated an integrated socio‐environmental analysis of the impacts of growing switchgrass within row‐crop landscapes in Illinois. In this study, we model land use scenarios that incorporate switchgrass as a biofuel crop in a Midwest corn‐belt watershed using the Soil Water Assessment Tool coupled with an economic analysis for the Vermilion Basin in Illinois. We estimated the values of ecosystem services under an alternative bioenergy landscape, including commodity and bioenergy crops, changes in biogeochemistry, and recreational services. The estimated annual values of nitrate and sediment reduction attributed to bioenergy crops range from $38 million to $97 million and $16,000 to $197,000, respectively. The annual value of carbon dioxide emission reduction ranges from $1.8 million to $6.1 million based on the initial crop rotation pattern. Estimated average annual values for wildlife viewing, water‐based recreation, and pheasant hunting are $1.24 million, $0.17 million, and $0.3 million, respectively. To our knowledge, this study represents the first effort to comprehensively quantify ecosystem services using a process‐based model, and estimate their value in an alternative bioenergy landscape. The information we generate could aid in understanding the potential for biomass production from marginal land and the total economic value of the landscape at various spatial scales. The framework is useful in fostering alternative bioenergy landscapes with synergies in a food, energy, and conservation nexus.     

Soil carbon stock impacts following reversion of Miscanthus × giganteus and short rotation coppice willow commercial plantations into arable cropping

There are posited links between the establishment of perennial bioenergy, such as short rotation coppice (SRC) willow and Miscanthus × giganteus, on low carbon soils and enhanced soil C sequestration. Sequestration provides additional climate mitigation, however, few studies have explored impacts on soil C stocks of bioenergy crop removal; thus, the permanence of any sequestered C is unclear. This uncertainty has led some authors to question the handling of soil C stocks with carbon accounting, for example, through life cycle assessments. Here, we provide additional data for this debate, reporting on the soil C impacts of the reversion (removal and return) to arable cropping of commercial SRC willow and Miscanthus across four sites in the UK, two for each bioenergy crop, with eight reversions nested within these sites. Using a paired‐site approach, soil C stocks (0–1 m) were compared between 3 and 7 years after bioenergy crop removal. Impacts on soil C stocks varied, ranging from an increase of 70.16 ± 10.81 Mg C/ha 7 years after reversion of SRC willow to a decrease of 33.38 ± 5.33 Mg C/ha 3 years after reversion of Miscanthus compared to paired arable land. The implications for carbon accounting will depend on the method used to allocate this stock change between current and past land use. However, with published life cycle assessment values for the lifetime C reduction provided by these crops ranging from 29.50 to 138.55 Mg C/ha, the magnitude of these changes in stock are significant. We discuss the potential underlying mechanisms driving variability in soil C stock change, including the age of bioenergy crop at removal, removal methods, and differences in the recalcitrant of the crop residues, and highlight the need to design management methods to limit negative outcomes.     

Identifying potential areas for biofuel production and evaluating the environmental effects: a case study of the James River Basin in the Midwestern United States

Biofuels are now an important resource in the United States because of the Energy Independence and Security Act of 2007. Both increased corn growth for ethanol production and perennial dedicated energy crop growth for cellulosic feedstocks are potential sources to meet the rising demand for biofuels. However, these measures may cause adverse environmental consequences that are not yet fully understood. This study 1) evaluates the long‐term impacts of increased frequency of corn in the crop rotation system on water quantity and quality as well as soil fertility in the James River Basin and 2) identifies potential grasslands for cultivating bioenergy crops (e.g. switchgrass), estimating the water quality impacts. We selected the soil and water assessment tool, a physically based multidisciplinary model, as the modeling approach to simulate a series of biofuel production scenarios involving crop rotation and land cover changes. The model simulations with different crop rotation scenarios indicate that decreases in water yield and soil nitrate nitrogen (NO₃‐N) concentration along with an increase in NO₃‐N load to stream water could justify serious concerns regarding increased corn rotations in this basin. Simulations with land cover change scenarios helped us spatially classify the grasslands in terms of biomass productivity and nitrogen loads, and we further derived the relationship of biomass production targets and the resulting nitrogen loads against switchgrass planting acreages. The suggested economically efficient (planting acreage) and environmentally friendly (water quality) planting locations and acreages can be a valuable guide for cultivating switchgrass in this basin. This information, along with the projected environmental costs (i.e. reduced water yield and increased nitrogen load), can contribute to decision support tools for land managers to seek the sustainability of biofuel development in this region.     

Consensus,uncertainties and challenges for perennial bioenergy crops and land use

Perennial bioenergy crops have significant potential to reduce greenhouse gas (GHG) emissions and contribute to climate change mitigation by substituting for fossil fuels; yet delivering significant GHG savings will require substantial land‐use change, globally. Over the last decade, research has delivered improved understanding of the environmental benefits and risks of this transition to perennial bioenergy crops, addressing concerns that the impacts of land conversion to perennial bioenergy crops could result in increased rather than decreased GHG emissions. For policymakers to assess the most cost‐effective and sustainable options for deployment and climate change mitigation, synthesis of these studies is needed to support evidence‐based decision making. In 2015, a workshop was convened with researchers, policymakers and industry/business representatives from the UK, EU and internationally. Outcomes from global research on bioenergy land‐use change were compared to identify areas of consensus, key uncertainties, and research priorities. Here, we discuss the strength of evidence for and against six consensus statements summarising the effects of land‐use change to perennial bioenergy crops on the cycling of carbon, nitrogen and water, in the context of the whole life‐cycle of bioenergy production. Our analysis suggests that the direct impacts of dedicated perennial bioenergy crops on soil carbon and nitrous oxide are increasingly well understood and are often consistent with significant life cycle GHG mitigation from bioenergy relative to conventional energy sources. We conclude that the GHG balance of perennial bioenergy crop cultivation will often be favourable, with maximum GHG savings achieved where crops are grown on soils with low carbon stocks and conservative nutrient application, accruing additional environmental benefits such as improved water quality. The analysis reported here demonstrates there is a mature and increasingly comprehensive evidence base on the environmental benefits and risks of bioenergy cultivation which can support the development of a sustainable bioenergy industry.     

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.     

Hydrologic and water quality impacts of biofuel feedstock production in the Ohio River Basin

This study addresses the uncertainties related to potential changes in land use and management and associated impacts on hydrology and water quality resulting from increased production of biofuel from the conventional and cellulosic feedstock. The Soil Water Assessment Tool (SWAT) was used to assess the impacts on regional and field scale evapotranspiration, soil moisture content, stream flow, sediment, and nutrient loadings in the Ohio River Basin. The model incorporates spatially and temporally detailed hydrologic, climate and agricultural practice data that are pertinent to simulate biofuel feedstock production, watershed hydrology and water quality. Three future biofuel production scenarios in the region were considered, including a feedstock projection from the DOE Billion‐Ton (BT2) Study, a change in corn rotations to continuous corn, and harvest of 50% corn stover. The impacts were evaluated on the basis of relative changes in hydrology and water quality from historical baseline and future business‐as‐usual conditions of the basin. The overall impact on water quality is an order of magnitude higher than the impact on hydrology. For all the three future scenarios, the sub‐basin results indicated an overall increase in annual evapotranspiration of up to 6%, a decrease in runoff up to 10% and minimal change in soil moisture. The sediment and phosphorous loading at both regional and field levels increased considerably (up to 40–90%) for all the biofuel feedstock scenario considered, while the nitrogen loading increased up to 45% in some regions under the BT2 Study scenario, decreased up to 10% when corn are grown continuously instead of in rotations, and changed minimally when 50% of the stover are harvested. Field level analyses revealed significant variability in hydrology and water quality impacts that can further be used to identify suitable locations for the feedstock productions without causing major impacts on water quantity and quality.     

Spatiotemporal land use modelling to assess land availability for energy crops – illustrated for Mozambique

A method and tool have been developed to assess future developments in land availability for bioenergy crops in a spatially explicit way, while taking into account both the developments in other land use functions, such as land for food, livestock and material production, and the uncertainties in the key determinant factors of land use change (LUC). This spatiotemporal LUC model is demonstrated with a case study on the developments in the land availability for bioenergy crops in Mozambique in the timeframe 2005–2030. The developments in the main drivers for agricultural land use, demand for food, animal products and materials were assessed, based on the projected developments in population, diet, GDP and self‐sufficiency ratio. Two scenarios were developed: a business‐as‐usual (BAU) scenario and a progressive scenario. Land allocation was based on land use class‐specific sets of suitability factors. The LUC dynamics were mapped on a 1 km² grid level for each individual year up to 2030. In the BAU scenario, 7.7 Mha and in the progressive scenario 16.4 Mha could become available for bioenergy crop production in 2030. Based on the Monte Carlo analysis, a 95% confidence interval of the amount of land available and the spatially explicit probability of available land was found. The bottom‐up approach, the number of dynamic land uses, the diverse portfolio of LUC drivers and suitability factors, and the possibility to model uncertainty mean that this model is a step forward in modelling land availability for bioenergy potentials.     

Bioenergy crops,biodiversity and ecosystem services in temperate agricultural landscapes—A review of synergies and trade-offs

The Paris agreement on climate change requires rapid reductions in greenhouse gas emissions. One important mitigation strategy, at least in the intermediate future, is the substitution of fossil fuels with bioenergy. However, using agriculture- and forest-derived biomass for energy has sparked controversy regarding both the climate mitigation potential and conflicts with biodiversity conservation. The urgency of the climate crisis calls for using forests for carbon sequestration and storage rather than for bioenergy, making agricultural biomass an attractive alternative for fossil energy substitution. However, this calls for comprehensive assessments of its sustainability in terms of consequences for biodiversity and ecosystem services. In this review, we provide a first holistic overview of the impacts on ecosystems of land-use changes from bioenergy crop production in temperate climates, by synthesizing results on both biodiversity and ecosystem service impacts. We found that bioenergy-related land-use changes can have both positive and negative effects on ecosystems, with original land use, bioenergy crop type and scale of bioenergy production being important moderators of impacts. Despite the risk of opportunity cost for food production, perennial crop cultivation on arable land had the lowest occurrence of negative impacts on biodiversity and ecosystem services. Growing biomass for bioenergy on surplus land has been suggested as a way to alleviate competition with food production and biodiversity conservation, but our results demonstrate that utilizing marginal or abandoned land for bioenergy crop production cannot fully resolve these trade-offs. Furthermore, there is a lack of empirical studies of the biodiversity value of marginal and abandoned land, limiting our understanding of the sustainability implications of biomass cultivation on surplus land. We argue that future research and policies for bioenergy production must explicitly consider biodiversity and ecosystem services in combination to avoid potential trade-offs between the two and to ensure sustainable bioenergy production.