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Perennial energy grasses have gained attention in recent years as a promising resource for the bioeconomy because of their benign environmental profile, high stress tolerance, high biomass yields and low input requirements. Currently, strong breeding efforts are being made to extend the range of commercially available miscanthus and switchgrass genotypes. In order to foster farmers' acceptance of these crops, and especially of novel hybrids, more information is required about how they can be efficiently integrated into cropping rotations, how they can be removed at the end of their productive lifespan, and what effect they have on subsequently grown crops. Farmers in Europe are meanwhile increasingly constrained in the methods available to them to remove these crops, and there is a risk that the herbicide glyphosate, which has been used in many studies to remove them, will be banned in coming years. This study looks at the removal of seven‐year‐old stands of miscanthus and switchgrass over 1 year at an experimental site in Southern‐Germany. Three novel miscanthus genotypes were studied, alongside one variety of switchgrass, and the impact of each crop's removal on the yield of maize grown as a follow‐on crop was examined. A combination of soil tillage and grass herbicides for maize cultivation was successful in controlling miscanthus regrowth, such that yields of maize grown after miscanthus did not differ significantly from yields of maize grown in monoculture rotation (18.1 t dry biomass ha−1). Yields of maize grown after switchgrass (14.4 t dry biomass ha−1) were significantly lower than maize in monoculture rotation caused by insufficient control of switchgrass regrowth by the applied maize herbicide. Although some regrowth of miscanthus and switchgrass was observed in the follow‐on crop maize, complete eradication of both crops was achieved by subsequent winter wheat cultivation. [ABSTRACT FROM AUTHOR]

The employment of biochar in crop production can not only improve soil quality, but also helps the field ecosystem to fix carbon and reduce emissions. Although the benefits of their application in crop production have been more and more confirmed, it is not clear when it comes to the acidic soil of tobacco and rice rotation. A tobacco–rice rotation experiment was conducted in southern China to probe the application value of biochar under these conditions. Three biochar application rates were employed in this experiment. BC0 (without biochar), BC25 (25 t ha−1), and BC50 (50 t ha−1). The findings show that biochar significantly boosted soil fertility and crop yields. Meanwhile, the soil organic carbon of tobacco rice rotation field with biochar increased by 31.76%. After a whole growth period of tobacco and rice, the cumulative emission reduction of CO2 and N2O from the soil by biochar were 15,944 kg ha−1 and 1810 g ha−1, respectively. The use of biochar not only significantly improved the bacterial diversity of tobacco and rice rotation soil, but also altered the original microbial community structure. The profusion of Proteobacteria and Acidobacteria was reduced and the abundance of Actinobacteria and Bacteroidetes was enhanced in the treatments with biochar. Among them, Sphingomonadales, Planctomycotes, and Ktedonobacteria, which are beneficial to plant growth and soil health, have become key phylotypes. The carbon balance analysis data show that the net carbon sequestration of the two treatments with biochar is positive, while that of the treatment without biochar is negative. In terms of economic benefit, the application of biochar increased the average of 2.055 CNY kg−1 consumed energy (CE) in the whole tobacco–rice rotation system. The ecological benefit was 0.51 kg C kg−1 CE. In conclusion, biochar can be effectively used in the practice of tobacco–rice rotation and acidic soil improvement in southern China. To explore the application value of biochar on acidic soil in south China, the effects of different application rates of biochar on crop production, carbon sequestration, and emission reduction were compared through a tobacco and rice rotation experiment. The results show that field application of biochar is not only economically feasible in agricultural production, but also has positive ecological benefits. [ABSTRACT FROM AUTHOR]

Determining optimal management practices for the profitable production of perennial energy crops is critical for scaling up production beyond experimental levels. Although many experimental field studies have examined the effects of management practices on the performance of miscanthus and switchgrass, there are no recommendations for economically optimal nitrogen (N) application rates and how they should vary spatially and with the age of the energy crop as well as on optimal rotation age of the energy crop to maximize profits. We develop a modeling framework to determine economically optimal crop management decisions and simulate the variability under various scenarios for miscanthus and switchgrass production across 2287 counties in the rainfed United States. We find that profit‐maximizing N recommendations for these crops vary across maturity stages and regions and can increase the landowner's profits compared with a uniform N rate across ages and regions. We also find that the optimal rotation for these crops is shorter than the productive physical lifespan (15–20 and 10 years for miscanthus and switchgrass, respectively). Specifically, the N rate that maximizes the economic returns is negligible for miscanthus and 111 kg ha−1 for switchgrass production at age 2. The mean profit‐maximizing N rate increases with age for miscanthus, peaking at 151 kg ha−1 at age 11 before declining to 114 kg ha−1 at the optimal rotation age of 13 years while that for switchgrass is 150 kg ha−1 for middle‐aged stands and declines to 114 kg ha−1 at the optimal rotation of 8–9 years. We find that miscanthus is the most profitable energy crop in the northern region of the rainfed United States while switchgrass is most profitable in the south of the rainfed United States. Our findings are useful for improving assessments of the profitability of energy crops and guiding future management decisions by landowners. Experimental field studies have examined the effects of management practices on the performance of miscanthus and switchgrass, but there are no recommendations for economically optimal nitrogen (N) application rates and how they should vary spatially and with the age of the energy crop as well as the optimal rotation age of these crops to maximize the economic returns. We develop a modeling framework to determine economically optimal management decisions for miscanthus and switchgrass production in the rainfed United States under various scenarios. Our findings are useful for guiding future energy crop management decisions by landowners. [ABSTRACT FROM AUTHOR]

The agriculture sector can contribute to climate change mitigation by reducing its own greenhouse gas (GHG) emissions, sequestering carbon in vegetation and soils, and providing biomass to substitute for fossil fuels and other GHG‐intensive products. The sector also needs to address water, soil, and biodiversity impacts caused by historic and current practices. Emerging EU policies create incentives for cultivation of perennial plants that provide biomass along with environmental benefits. One such option, common in northern Europe, is to include grass in rotations with annual crops to provide biomass while remediating soil organic carbon (SOC) losses and other environmental impacts. Here, we apply a spatially explicit model on >81,000 sub‐watersheds in EU27 + UK (Europe) to explore the effects of widespread deployment of such systems. Based on current accumulated SOC losses in individual sub‐watersheds, the model identifies and quantifies suitable areas for increased grass cultivation and corresponding biomass‐ and protein supply, SOC sequestration, and reductions in nitrogen emissions to water as well as wind and water erosion. The model also provides information about possible flood mitigation. The results indicate a substantial climate mitigation potential, with combined annual GHG savings from soil‐carbon sequestration and displacement of natural gas with biogas from grass‐based biorefineries, equivalent to 13%–48% of current GHG emissions from agriculture in Europe. The environmental co‐benefits are also notable, in some cases exceeding the estimated mitigation needs. Yield increases for annual crops in modified rotations mitigate the displacement effect of increasing grass cultivation. If the grass is used as feedstock in lieu of annual crops, the displacement effect can even be negative, that is, a reduced need for annual crop production elsewhere. Incentivizing widespread deployment will require supportive policy measures as well as new uses of grass biomass, for example, as feedstock for green biorefineries producing protein concentrate, biofuels, and other bio‐based products. [ABSTRACT FROM AUTHOR]

Monoculture croplands are a major source of global anthropogenic emissions of nitrous oxide (N2O), a potent greenhouse gas that contributes to ozone depletion. Agroforestry has the potential to reduce N2O emissions. Presently, there is no systematic comparison of soil N2O emissions between cropland agroforestry and monoculture systems in Central Europe. We investigated the effects of converting the monoculture cropland system into the alley cropping agroforestry system on soil N2O fluxes at three sites (each site has paired agroforestry and monoculture) in Germany, where agroforestry combined crop rows and poplar short‐rotation coppice (SRC). We measured soil N2O fluxes monthly over 2 years (March 2018–January 2020) using static vented chambers. Annual soil N2O emissions from agroforestry ranged from 0.21 to 2.73 kg N ha−1 year−1, whereas monoculture N2O emissions ranged from 0.34 to 3.00 kg N ha−1 year−1. During the rotation of corn crop, with high fertilization rates, agroforestry reduced soil N2O emissions by 9% to 56% compared to monocultures. This was mainly caused by low soil N2O emissions from the unfertilized agroforestry tree rows. Soil N2O fluxes were predominantly controlled by soil mineral N in both agroforestry and monoculture systems. Our findings suggest that optimized fertilizer input will further enhance the potential of agroforestry for mitigating N2O emissions. [ABSTRACT FROM AUTHOR]

Two major global challenges related to agriculture are climate change and the unbalanced nitrogen cycle. For both, national and international reduction targets have been defined to catalyse policy support for more sustainable farming systems. Miscanthus cultivation in water protection areas has been proposed as a contribution to achieving these targets. However, a thorough understanding of the underlying system dynamics at various spatial levels is required before recommendations for policy development can be provided. In this study, a model framework was established to provide economic and environmental indicator results at regional and sub-regional levels. It presents a consequential Life Cycle Assessment coupled with an agro-economic supply model (Economic Farm Emission Model) that simulates crop and livestock production, and an agricultural hydrology model (DAISY) that assesses effects on the nitrogen cycle. The framework is applied to Baden-Württemberg, a federal state in southwest Germany with eight agro-ecological regions. Scenarios investigating the differences between mandatory and voluntary miscanthus cultivation were also explored. While the results show the high potential of miscanthus cultivation for the reduction of greenhouse gas emissions (-16% to -724%), the potential to reduce nitrate leaching (-4% to -44%) is compromised in some sub-regions and scenarios (+4% to +13%) by substantial effects on the crop rotation. Furthermore, the cultivation of miscanthus reduces gross margins in most sub regions (-0.1% to -9.6%) and decreases domestic food production (-1% to -50%). However, in regions with low livestock density and high yields, miscanthus cultivation can maintain or increase farmers' income (0.1%-5.8%) and improve environmental protection. The study shows that the heterogeneity of arable land requires a flexible promotion programme for miscanthus. Voluntary cultivation schemes were identified as most suitable to capture sub-regional differences. Policies should address the demand for miscanthus, for example, support the development of regional value chains, including farmers, water suppliers and the biobased industry. [ABSTRACT FROM AUTHOR]

The adoption of a bioenergy crop is affected by various factors, including but not limited to the characteristics of farmers, farm economics, market forces, and physical environment. This study develops a spatially explicit agent‐based model for ascertaining the adoption rate of carinata (Brassica carinata) among the farmers in the Little River Experimental Watershed located in the southern state of Georgia in the United States. Each farmer's adoption behavior is modeled using the profitability difference between traditional crop rotations (with and without carinata at different contract prices), the adoption rate of neighboring farmers, and their land allocation decisions from managing a risky portfolio of enterprises. Carinata production in the winter season once every 3 years has no conflict with the most profitable and popular traditional row crop rotations, such as cotton‐cotton‐cotton and cotton‐cotton‐peanut, to a larger extent. The results show that 28% and 85% of farmers in the watershed will adopt carinata after 33 years at a contract price of $13/bushel (bu) under two different assumptions of low (2.5%) and high (5%) initial neighborhood adoption rates. The proportions of land allocated to carinata to the total farmland under field crops are 38% and 85% after 33 years under the same low and high neighborhood adoption rates, respectively. Our results suggest that fixing the appropriate contract price of carinata will bring additional profits to farmers without any significant foreseeable agronomic risks, thereby increasing the adoption rate of carinata at a regional level. [ABSTRACT FROM AUTHOR]

Poplars (Populus spp.) managed in short rotation woody crop (SRWC) systems are considered very promising in terms of biomass production for energy purposes in a temperate zone. In this study, several gaps in knowledge regarding the selection of the plant material, cultivar‐specific responses to coppicing and rotation length are addressed. Five‐ and 10‐year rotation lengths were considered, with a focus on the sustainability of the plantation and the quantification of the biomass production of 10 commercially available hybrid poplar cultivars during two consecutive 5‐year rotation cycles versus one 10‐year rotation in northern Poland. The biomass production varied considerably among cultivars, ranging from 1.6 ('AF8') to 7.5 ('NE42') Mg ha−1 year−1 at the end of the first 5‐year rotation, and 0.0 ('AF8')–5.4 ('Degrosso') Mg ha−1 year−1 in the second 5‐year rotation, while in a single 10‐year rotation, the mean annual increment (MAI) ranged from 1.0 ('AF8') to 15.1 ('NE42') Mg ha−1 yr−1. The 5‐year rotation cycles negatively influenced the sustainability of the plantation due to the high mortality of stems and sprouts in the second 5‐year coppice rotation. In the case of 5‐year and longer rotations, replanting (not resprouting) after harvest may be a more advantageous practice for maximizing the regeneration. The 10‐year rotation cycle allowed for enough development of the crown and root systems to produce sufficient basal area and height to achieve maximal MAI in the trees. The study revealed that an age ≥10 is a biologically optimal rotation age as the slope of MAI was equal/close to zero. This study further showed the crucial importance of testing cultivars before introducing them on a commercial scale and provided valuable information on poplar cultivars available to stakeholders in the biomass market. [ABSTRACT FROM AUTHOR]

Brassica carinata A. Braun is a non‐edible, oilseed winter crop for biofuel production that can diversify crop rotations and improve integrated weed management. The research objective was to evaluate the influence of B. carinata on weed population dynamics in the southeastern United States cropping systems. B. carinata was grown after cotton (Gossypium hirsutum L.), peanut (Arachis hypogea L.), or a clean summer fallow, and winter weed pressure was modified with or without S‐metolachlor. The emergence of Lamium amplexicaule L. increased at least 40% after cotton or peanut in 2018–2019 and 50% after cotton in 2019–2020 compared to summer fallow. Stellaria media (L.) Vill. emergence was increased over threefold after peanut or cotton in 2019–2020. Senna obtusifolia (L.) H.S. Irwin & Barneby emergence after cotton was increased at least 43% during both experimental years, whereas Amaranthus hybridus L. emergence was increased over 50% after peanut in 2019–2020 compared to summer fallow. Even without S‐metolachlor, B. carinata reduced A. hybridus (>27%) and S. obtusifolia (>25%) emergence compared to weedy winter fallow. After B. carinata harvest, A. hybridus emergence was reduced >40% with or without S‐metolachlor compared to winter fallow in 2018–2019. Overall, B. carinata biomass was highest after peanut for both seasons. B. carinata seed yield did not differ among crop history treatments in the first season, whereas in 2019–2020, the yield was higher after peanut (2417 kg ha−1) or fallow (2520 kg ha−1) compared to cotton (1710 kg ha−1). Weed management treatments were not different for B. carinata biomass or yield in any year. The results indicate that B. carinata can enhance integrated weed management strategies at the rotational level for summer crops by reducing seed banks of summer weed species, in addition to its potential as a winter biofuel crop for the southeastern United States. [ABSTRACT FROM AUTHOR]

Mallee eucalypts are being developed as a short rotation coppice crop for integration into agricultural systems in the south‐west of Western Australia. These have potential for biomass production for bioenergy, eucalyptus oil and generating carbon credits and to help control the extensive occurrence of dryland salinity. Some 12,000 ha of mallee planting has been undertaken since 1994, mostly in the form of wide‐spaced, narrow belts within the annual agricultural system. Production and market data were used to estimate levelized costs (LC) of mallee biomass production under different harvest regimes across 11 sites from 2006 to 2012. We found LC ranged from AUD40 to AUD257 fresh Mg−1. LC was most strongly determined by mallee production, followed by the crop/pasture rotation decisions of the landholder. Mallee harvest regime had minor impact on LC. Crop and pasture yield loss due to competition from the mallee belts accounted for 38% of costs, harvesting biomass was 32%, opportunity cost of the land occupied by the mallee belts was 16% while establishment and maintenance costs accounted for 14% of the costs. When income from carbon sequestered in mallee root biomass was included, the LC dropped by an average of 11% at the current Australian price of AUD15 Mg−1 CO2 equivalent (CO2e). The income from carbon sequestered in root biomass alone is unlikely to make mallee agroforestry economically viable. Hence, income from harvested biomass in the form of feedstocks for industry or carbon credits is necessary to make mallee agroforestry commercially attractive. LC for unharvested mallee belts ranged from AUD33 to AUD237 Mg−1. Where above‐ and below‐ground biomass is converted to CO2e at AUD15 Mg−1, the LC drops to AUD11–AUD64, with three of 11 sites likely to be profitable. These three sites were characterized by high biomass production with low agricultural gross margins. [ABSTRACT FROM AUTHOR]

In the age of biofuel innovation, bioenergy crop sustainability assessment has determined how candidate systems alter the carbon (C) and nitrogen (N) cycle. These research efforts revealed how perennial crops, such as switchgrass, increase belowground soil organic carbon (SOC) and lose less N than annual crops, like maize. As demand for bioenergy increases, land managers will need to choose whether to invest in food or fuel cropping systems. However, little research has focused on the C and N cycle impacts of reverting purpose‐grown perennial bioenergy crops back to annual cropping systems. We investigated this knowledge gap by measuring C and N pools and fluxes over 2 years following reversion of a mature switchgrass stand to an annual maize rotation. The most striking treatment difference was in ecosystem respiration (ER), with the maize‐converted treatment showing the highest respiration flux of 2,073.63 (± 367.20) g C m−2 year−1 compared to the switchgrass 1,412.70 (± 28.72) g C m−2 year−1 and maize‐control treatments 1,699.16 (± 234.79) g C m−2 year−1. This difference was likely driven by increased heterotrophic respiration of belowground switchgrass necromass in the maize‐converted treatment. Predictions from the DayCent model showed it would take approximately 5 years for SOC dynamics in the converted treatment to return to conditions of the maize‐control treatment. N losses were highest from the maize‐converted treatment when compared to undisturbed switchgrass and maize‐control, particularly during the first conversion year. These results show substantial C and N losses occur within the first 2 years after reversion of switchgrass to maize. Given farmers are likely to rotate between perennial and annual crops in the future to meet market demands, our results indicate that improvements to the land conversion approach are needed to preserve SOC built up by perennial crops to maintain the long‐term ecological sustainability of bioenergy cropping systems. [ABSTRACT FROM AUTHOR]

Willow biomass produced in short rotation coppice systems can potentially be used as biomass feedstock in Europe, the United States and Canada. However, most researchers focus on data from the first harvest rotation only, whereas multiple rotations have been rarely investigated. The aim of this study was to evaluate the effect of cultivar (5), planting density (12,000–96,000 cuttings/ha) and harvest rotation (annual, biennial, triennial) on willow biomass yields during 12 consecutive years in northern Poland. Every experimental factor and the interactions between factors significantly impacted willow yields. Biomass yield was highest in the triennial harvest rotation (13.3 Mg ha−1 year−1), 15.9% lower in the biennial rotation and 26.9% lower in the annual rotation. The highest average yield (14.6 Mg ha−1 year−1) was noted at a planting density of 24,000 cuttings/ha, and yields were 9.3%–46.0% lower at the remaining densities. Cultivar UWM 095 had the highest average yield (13.0 Mg ha−1 year−1), whereas the yield of the remaining cultivars was 4.6%–32.4% lower. During the 12‐year period, yields were higher after the first harvest in annual, biennial and triennial harvest rotations. This above implies that high biomass yields can be obtained after the first harvest rotation if willows are cultivated on fertile soils at higher planting density, well managed and coppiced after the first year. However, yields are unlikely to be higher in successive harvest rotations, and they can even be lower, but more stable than in the first harvest rotation. Research on willow production focuses on data from the first harvest rotation only, whereas multiple rotations have been rarely investigated. We evaluate the effect of cultivar (5), planting density (4) and harvest rotation (3) on willow yields during twelve consecutive years. The results show that high yields can be obtained after the first harvest rotation if willows are cultivated on fertile soils at higher planting density, well managed and coppiced after the first year. However, yields are unlikely to be higher in successive harvest rotations, and they can even be lower, but more stable than in the first harvest rotation. [ABSTRACT FROM AUTHOR]

In the future, the lignocellulosic perennial crops short rotation coppice (SRC) and miscanthus are supposed to provide renewable raw materials for a bio‐based economy. To assess the potential regional supply of these crops, which are not yet widespread in Baden–Wuerttemberg (Southwest Germany), we used a two‐step approach. In a first step, we conducted a Discrete Choice Experiment (DCE) in regions of Baden–Wuerttemberg that—given their site conditions—are suitable for SRC or miscanthus. The respondents were characterized by significant preference heterogeneity for both (negatively valued) perennial crops and for all presented choice attributes. Thus, it was appropriate to estimate a random parameter logit model (RPL). The attributes average yearly contribution margin, long‐term purchase guarantee and cultivation by colleagues in the neighborhood had a significantly positive effect on the likelihood of cultivation, whereas the attributes contribution margin variability and initial investment need showed a significantly negative effect. In a second step, assuming realistic values for the levels of the attributes considered in the DCE, in stochastic simulations, we randomly draw part‐worth utilities from the multivariate normal distribution of these parameters according to the RPL results. This way, for alternative biomass prices, we derived shares of farmers' willing to engage in perennial crop production and produced related regional supply functions. Under moderate yield and realistic input and farmland opportunity cost assumptions, the full regional miscanthus potential can only be achieved when farmers are offered either subsidies or price‐risk‐reducing long‐term contracts. Based on empirically determined heterogeneous farmer preferences, our two‐step approach is suitable to yield realistic estimations of any not yet implemented farming practices. We finally note caveats related to our analysis and discuss some policy implications of the major findings. In the future, lignocellulosic perennial crops like miscanthus may provide renewable raw materials. In this context, the potential regional supply of such crops is of interest for economic actors and policy makers. We used a two‐step approach to elicit potential supply. In a first step, we conducted a Discrete Choice Experiment (DCE) among farmers in suitable regions of Southwest Germany. In a second step, assuming realistic levels of the attributes considered in the DCE and making use of the preference heterogeneity found in the DCE, in stochastic simulations, we derived regional perennial crop supply functions for alternative scenarios. [ABSTRACT FROM AUTHOR]

Abstract: The productivity of short‐rotation coppice (SRC) plantations with poplar (Populus spp.) strongly depends on soil water availability, which limits the future development of its cultivation, and makes the study of the transpirational water loss particularly timely under the ongoing climate change (more frequent drought and floods). This study assesses the transpiration at different scales (leaf, tree and stand) of four poplar genotypes belonging to different species and from a different genetic background grown under an SRC regime. Measurements were performed for an entire growing season during the third year of the third rotation in a commercial scale multigenotype SRC plantation in Flanders (Belgium). Measurements at leaf level were performed on specific days with a contrasted evaporative demand, temperature and incoming shortwave radiation and included stomatal conductance, stem and leaf water potential. Leaf transpiration and leaf hydraulic conductance were obtained from these measurements. To determine the transpiration at the tree level, single‐stem sap flow using the stem heat balance (SHB) method and daily stem diameter variations were measured during the entire growing season. Sap flow‐based canopy transpiration (Ec), seasonal dry biomass yield, and water use efficiency (WUE; g aboveground dry matter/kg water transpired) of the four poplar genotypes were also calculated. The genotypes had contrasting physiological responses to environmental drivers and to soil conditions. Sap flow was tightly linked to the phenological stage of the trees and to the environmental variables (photosynthetically active radiation and vapor pressure deficit). The total Ec for the 2016 growing season was of 334, 350, 483 and 618 mm for the four poplar genotypes, Bakan, Koster, Oudenberg and Grimminge, respectively. The differences in physiological traits and in transpiration of the four genotypes resulted in different responses of WUE. [ABSTRACT FROM AUTHOR]

Uruguay is pursuing renewable energy production pathways using feedstocks from its agricultural sector to supply transportation fuels, among them ethanol produced from commercial technologies that use sweet and grain sorghum. However, the environmental performance of the fuel is not known. We investigate the life cycle environmental and cost performance of these two major agricultural crops used to produce ethanol that have begun commercial production and are poised to grow to meet national energy targets for replacing gasoline. Using both attributional and consequential life cycle assessment ( LCA) frameworks for system boundaries to quantify the carbon intensity, and engineering cost analysis to estimate the unit production cost of ethanol from grain and sweet sorghum, we determined abatement costs. We found 1) an accounting error in estimating N2O emissions for a specific crop in multiple crop rotations when using Intergovernmental Panel on Climate Change( IPCC) Tier 1 methods within an attributional LCA framework, due to N legacy effects; 2) choice of baseline and crop identity in multiple crop rotations evaluated within the consequential LCA framework both affect the global warming intensity ( GWI) of ethanol; and 3) although abatement costs for ethanol from grain sorghum are positive and from sweet sorghum they are negative, both grain and sweet sorghum pathways have a high potential for reducing transport fuel GWI by more than 50% relative to gasoline, and are within the ranges targeted by the US renewable transportation fuel policies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

GHG mitigation by bioenergy crops depends on crop type, management practices, and the input of residue carbon (C) to the soil. Perennial grasses may increase soil C compared to annual crops because of more extensive root systems, but it is less clear how much soil C is derived from above- vs. belowground inputs. The objective of this study was to synthesize the existing knowledge regarding soil C inputs from above- and belowground crop residues in regions cultivated with sugarcane, corn, and miscanthus, and to predict the impact of residue removal and tillage on soil C stocks. The literature review showed that aboveground inputs to soil C (to 1-m depth) ranged from 70% to 81% for sugarcane and corn vs. 40% for miscanthus. Modeled aboveground C inputs (to 30 cm depth) ranged from 54% to 82% for sugarcane, but were 67% for miscanthus. Because 50% of observed miscanthus belowground biomass is below 30 cm depth, it may be necessary to increase the depth of modeled soil C dynamics to reconcile modeled belowground C inputs with measured. Modeled removal of aboveground corn residue (25-100%) resulted in C stock reduction in areas of corn-corn-soybean rotation under conventional tillage, while no-till management lessoned this impact. In sugarcane, soil C stocks were reduced when total aboveground residue was removed at one site, while partial removal of sugarcane residue did not reduce soil C stocks in either area. This study suggests that aboveground crop residues were the main C-residue source to the soil in the current bioethanol sector (corn and sugarcane) and the indiscriminate removal of crop residues to produce cellulosic biofuels can reduce soil C stocks and reduce the environmental benefits of bioenergy. Moreover, a switch to feedstocks such as miscanthus with more allocation to belowground C could increase soil C stocks at a much faster rate. [ABSTRACT FROM AUTHOR]

The demand for bioenergy has increased the interest in short-rotation woody crops ( SRWCs) in temperate zones. With increased litter input and ceased annual soil cultivation, SRWC plantations may become soil carbon sinks for climate change mitigation. A chronosequence of 26 paired plots was used to study the potential for increasing soil organic carbon ( SOC) under SRWC willow and poplar after conversion from cropland ( CR) on well-drained soils. We estimated SOC stocks in SRWC stands and adjacent CR and related the difference to time since conversion, energy crop species, SOC stock of the adjacent CR (proxy for initial SOC of SRWC) and the fine soil percentage (<63 μm) ( FS). Soil cores to 40 cm depth were sampled and separated by layers of fixed depths (0-5, 5-10, 10-15, 15-25 and 25-40 cm). Additionally, soils were sampled from soil pits by genetic horizons to 100 cm depth. Comparisons of SOC stocks by equivalent soil masses showed that mean SOC stocks in SRWC were 1.7 times higher than those of CR in the top 5 cm of the soil ( P < 0.001). The differences between SRWC and CR remained significant for the plough layer (0-25 cm) by a factor of 1.2 ( P = 0.003), while no changes were detectable for the 0-40 cm ( P = 0.32), or for the entire 0-100 cm soil layer ( P = 0.29). The SOC stock ratio, that is the ratio of SOC stock in SRWC relative to CR, did not change significantly with time since conversion, although there was a tendency to an increase over time for the top 40 cm ( P = 0.09). The SOC stock ratio was negatively correlated to SOC in CR and FS percentage, but there was no significant difference between willow and poplar at any depth. Our results suggest that SOC stocks in the plough layer increase after conversion to SRWC. [ABSTRACT FROM AUTHOR]

We calibrated and evaluated the agricultural model AquaCrop for the simulation of water use and yield of a short-rotation coppice (SRC) plantation with poplar ( Populus) in East Flanders (Belgium) during the second and the third rotation (first 2 years only). Differences in crop development and growth during the course of the rotations were taken into account during the model calibration. Overall, the AquaCrop model showed good performance for the daily simulation of soil water content ( R2 of 0.57-0.85), of green canopy cover ( R2 > 0.87), of evapotranspiration (ET; R2 > 0.76), and of potential yield. The simulated, total yearly water use of the SRC ranged between 55% and 85% of the water use of a reference grass ecosystem calculated under the same environmental conditions. Crop transpiration was between 67% and 93% of total ET, with lower percentages in the first than in the second year of each rotation. The observed (dry mass) yield ranged from 6.61 to 14.76 Mg ha−1 yr−1. A yield gap of around 30% was observed between the second and the third rotation, as well as between simulated and observed yield during the third rotation. This could possibly be explained by the expansion of the understory (weed) layer; the relative cover of understory weeds was 22% in the third year of the third rotation. The agricultural AquaCrop model simulated total water use and potential yield of the operational SRC in a reliable way. As the plantation was extensively managed, potential effects of irrigation and/or fertilization on ET and on yield were not considered in this study. [ABSTRACT FROM AUTHOR]

Feed in tariffs (FiTs) and renewable heat incentives ( RHIs) are driving a rapid expansion in anaerobic digestion ( AD) coupled with combined heat and power ( CHP) plants in the UK. Farm models were combined with consequential life cycle assessment ( CLCA) to assess the net environmental balance of representative biogas, biofuel and biomass scenarios on a large arable farm, capturing crop rotation and digestate nutrient cycling effects. All bioenergy options led to avoided fossil resource depletion. Global warming potential ( GWP) balances ranged from −1732 kg CO2e Mg−1 dry matter ( DM) for pig slurry AD feedstock after accounting for avoided slurry storage to +2251 kg CO2e Mg−1 DM for oilseed rape biodiesel feedstock after attributing indirect land use change ( iLUC) to displaced food production. Maize monoculture for AD led to net GWP increases via iLUC, but optimized integration of maize into an arable rotation resulted in negligible food crop displacement and iLUC. However, even under best-case assumptions such as full use of heat output from AD- CHP, crop-biogas achieved low GWP reductions per hectare compared with Miscanthus heating pellets under default estimates of iLUC. Ecosystem services (ES) assessment highlighted soil and water quality risks for maize cultivation. All bioenergy crop options led to net increases in eutrophication after displaced food production was accounted for. The environmental balance of AD is sensitive to design and management factors such as digestate storage and application techniques, which are not well regulated in the UK. Currently, FiT payments are not dependent on compliance with sustainability criteria. We conclude that CLCA and ES effects should be integrated into sustainability criteria for FiTs and RHIs, to direct public money towards resource-efficient renewable energy options that achieve genuine climate protection without degrading soil, air or water quality. [ABSTRACT FROM AUTHOR]

The paper presents a model system, which consists of a partial equilibrium model and process-based terrestrial biogeochemistry models, to determine the optimal distributions of both Miscanthus ( Miscanthus × giganteus) and short rotation coppice willow ( SRC) ( Salix. viminalis L. x S. viminalis var Joruun) in Great Britain ( GB), as well as their potential contribution to meet heat and electricity demand in GB. Results show that the potential contribution of Miscanthus and SRC to heat and electricity demand is significant. Without considering farm-scale economic constraints, Miscanthus and SRC could generate, in an economically competitive way compared with other energy generation costs, 224 800 GWh yr−1 heat and 112 500 GWh yr−1 electricity, with 8 Mha of available land under Miscanthus and SRC, accounting for 66% of total heat demand and 62% of total electricity demand respectively. Given the pattern of heat and electricity demand, and the relative yields of Miscanthus and SRC in different parts of GB, Miscanthus is mainly favoured in the Midlands and areas in the South of GB, whereas SRC is favoured in Scotland, the Midlands and areas in the South of GB. [ABSTRACT FROM AUTHOR]

Process and empirical-based models that describe lignocellulosic biomass yield of the perennial energy grass Miscanthus (MiscanFor©), short rotation coppice ( SRC) trees and shrubs, poplar and willow (ForestGrowth- SRC) and a number of short rotation forest trees ( ESC- CARBINE), were used to estimate the yield potential for current and future climates across Great Britain ( GB). In current climates, modelled yields for all feedstock crops varied between 8.1 and 10.6 Mg dry weight ( DW) ha−1 yr−1 with willow SRC and poplar SRF producing the lowest and highest yields respectively. For the medium emissions scenario ( UKCP09) in 2050, mean yield for all feedstock crops varied between 7.6 and 12.7 Mg DW ha−1 yr−1 with willow SRC and poplar SRF once again the lowest and the highest recorded yields. There were clear geographical trends within GB. Miscanthus yield was higher than all others in the south-west (13.1 Mg DW ha−1 yr−1), SRC willow and SRC poplar in the north-west (12.1-15.8 Mg DW ha−1 yr−1) and in the midlands and south-east, SRF poplar was the highest yielding (10.5-11.6 Mg DW ha−1 yr−1). These geographical trends changed little with climate out to 2050, with mean yield of each 'best feedstock' increasing from 12.7 to 14.2 Mg DW ha−1 yr−1. Out to 2050, SRC declined slightly and Miscanthus and SRF poplar increased as the 'best feedstock' option. Except for a few localized examples, only SRF poplar had a higher yield than SRC or Miscanthus. These data suggest that in current and future climates, lignocellulosic biomass plantation species can be selected and optimized for best yield performance in different regions of GB. This modelling framework provides a valuable starting-point for which to test the performance of new genetic material, as this becomes available and parameterized for the models and socio-economic scenarios that may impact on the bioenergy industry. [ABSTRACT FROM AUTHOR]

To achieve the UK Government's aim of expansion in the growth of perennial energy crops requires farmers to select these crops in preference to conventional rotations. Existing studies estimating the total potential resource have either only simplistically considered the farmer decision-making and opportunity costs, for example using an estimate of annual land rental charge; or have not considered spatial variability, for example using representative farm types. This paper attempts to apply a farm-scale modelling approach with spatially specific data to improve understanding of potential perennial energy crop supply. The model main inputs are yield maps for the perennial energy crops, Miscanthus and willow grown as short-rotation coppice ( SRC), and regional yields for conventional crops. These are used to configure location specific farm-scale models, which optimize for profit maximization with risk aversion. Areas that are unsuitable or unavailable for energy crops, due to environmental or social factors, are constrained from selection. The results are maps of economic supply, assuming a homogenous farm-gate price, allowing supply cost curves for the UK market to be derived. The results show a high degree of regional variation in supply, with different patterns for each energy crop. Using estimates of yields under climate change scenarios suggests that Miscanthus supply may increase under future climates while the opposite effect is suggested for SRC willow. The results suggest that SRC willow is only likely to able to supply a small proportion of the anticipated perennial energy crop target, without increases in market prices. Miscanthus appears to have greater scope for supply, and its dominance may be amplified over time by the effects of climate change. Finally, the relationship to the demand side of the market is discussed, and work is proposed to investigate the factors impacting how the market as a whole may develop. [ABSTRACT FROM AUTHOR]

To diversify energy crop production and improve its biodiversity and sustainability, there is currently a search for alternative energy crops. Many of the newly arising alternatives are perennial species such as the C4 grass miscanthus. The assessment of reliable data is a prerequisite for understanding the performance of these crops and developing corresponding management systems. However there is great uncertainty concerning research methodology for these crops. When data are collected from small plots of perennial crops, such as miscanthus or short rotation coppice plantations, a larger variability is expected than for cereals. A square meter cut, corresponding to harvest practice in cereals, is not sufficient for perennial C4 grasses and is not recommended for these species. The aim of this research was to identify an adequate size of sampling area for miscanthus to estimate the true biomass yield or quality. For this purpose, whole plots of 10- and 14-year old miscanthus stands were divided into smaller subplots. These were used to calculate variances for various sizes of simulated plots. The variances for all traits in the experiments were rather high when the sampling area was smaller than 2 m². A cutting regime of more than 5.6 m² would be advisable, but an area of 3 m² is sufficient to eliminate approximately 90% of the variances and is therefore an adequate size of sampling area. [ABSTRACT FROM AUTHOR]

Nitrous oxide emissions are of critical importance for the assumed climate neutrality of bio-energy. In this study we report on the N2 O fluxes from a bio-energy poplar plantation measured with eddy covariance for 2 years, after conversion of agricultural fields to few months after harvesting of the plantation. A pulse peak of N2 O was detected after the land use change and in the wake of the first heavy rainfall. The N2 O- N emission during just a single week was 2.7 kg N2 O- N ha−1 which represented approximately 42% of the total N2 O- N emitted during the 2 years of measurements. After this peak emission, N2 O fluxes were constantly rather low, not increasing after rainfall events any longer. Lowest emissions (and even N2 O sink) occurred mostly during the end of the second growing season with maximum canopy development, and water table deeper than 80 cm. Gross primary production ( GPP) explained 68% of the monthly averaged variability in N2 O emission from August to December 2011. Probably N uptake by vegetation during the peak of the second growing season limited N2 O emission, which in fact increased again after the plantation was coppiced. For the majority of the measuring period, N2 O fluxes did not present a well-defined diurnal pattern, with the exception of two periods: (1) from 19-22 August 2010 and (2) from September-November 2011. In both cases wind speed played a major role in controlling the diurnal pattern in these fluxes (explaining up to 80% of the diurnal variability in N2 O fluxes on 19-22 August 2010), whereas at the end of the second growing season (September-November 2011), GPP explained 73% of the diurnal pattern in N2 O fluxes. [ABSTRACT FROM AUTHOR]

There is a growing need for all productive sectors to develop greenhouse gas ( GHG) mitigation techniques to reduce the enhanced greenhouse effect. However, the challenge to the agricultural sector is reducing net emissions while increasing production to meet growing demands for food, fiber, and biofuel. This study focuses on the changes in the GHG balance when sugarcane areas are converted from burned harvest ( BH) to green harvest ( GH, mechanized harvest), including the changes caused by the adoption of conservationist practices such as reduced tillage and a 4-month crop rotation with Crotalaria juncea L. during sugarcane replanting. Based on the Intergovernmental Panel on Climate Change (IPCC) (2006) methodologies, the annual emission balance includes both agricultural and mobile sources of GHG, according to the mean annual consumption of supplies per hectare. The potential soil carbon accumulation was also considered in the GH plot. The total amounts of GHG were 2651.9 and 2316.4 kg CO2eq ha−1 yr−1 for BH and GH, respectively. Factoring in a mean annual soil carbon accumulation rate of 888.1 kg CO2 ha−1 yr−1 due to the input from long-term crop residues associated with the conversion from BH to GH, the emission balance in GH decreased to 1428.3 kg CO2eq ha−1 yr−1. A second decrease occurs when a reduced tillage strategy is adopted instead of conventional tillage during the replanting season in the GH plot, which helps reduce the total emission balance to 1180.3 kg CO2eq ha−1 yr−1. Moreover, the conversion of sugarcane from BH to GH, with the adoption of a crop rotation with Crotalaria juncea L. as well as reduced tillage during sugarcane replanting, would result in a smaller GHG balance of 1064.6 kg CO2eq ha−1 yr−1, providing an effect strategy for GHG mitigation while still providing cleaner sugar and ethanol production in southern Brazil. [ABSTRACT FROM AUTHOR]

The demand for wood from short rotation coppice ( SRC) plantations as a renewable energy source is currently increasing and could affect biodiversity in agricultural areas. The objective was to evaluate the contribution of SRC plantations to phytodiversity in agricultural landscapes assessed as species richness, species-area relationships, Shannon indices, detrended correspondence analysis on species composition, Sørensen similarities, habitat preference proportions, and species proportions found in only one land use. Vegetation surveys were conducted on 12 willow ( Salix spp.) and three poplar ( Populus spp.) coppice sites as well as on surrounding arable lands, grasslands and forests in central Sweden and northern Germany. SRC plantations were richer in plant species (mean: 30 species per 100 m²) than arable land (10), coniferous forests (13) and mixed forests in Germany (12). Comparing SRC plantations with other land uses, we found lowest similarities in species composition with arable lands, coniferous forests and German mixed forests and highest similarities with marginal grassland strips, grasslands and Swedish mixed forests. Similarity depended on the SRC tree cover: at increased tree cover, SRC plantations became less similar to grasslands but more similar to forests. The SRC plantations were composed of a mixture of grassland (33%), ruderal (24%) and woodland (15%) species. Species abundance in SRC plantations was more heterogeneous than in arable lands. We conclude that SRC plantations form novel habitats leading to different plant species composition compared to conventional land uses. Their landscape-scale value for phytodiversity changes depending on harvest cycles and over time. As a structural landscape element, SRC plantations contribute positively to phytodiversity in rural areas, especially in land use mosaics where these plantations are admixed to other land uses with dissimilar plant species composition such as arable land, coniferous forest and, at the German sites, also mixed forest. [ABSTRACT FROM AUTHOR]