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To meet the growing challenges of food security, sufficient biomass for biorefineries and mitigation of climate change, perennial grass is recommended as an alternative for annual grain crop to increase biomass production while protecting soil C stock. However, the long-term biomass yield production, soil C stock, and ecosystem CO2 flux are rarely simultaneously evaluated in the same study site, limiting the understanding of C flows in different cropping systems. We compared the annual grain crop triticale (Triticosecale) grown every year since 2012 with the productive perennial grass festulolium (Festulolium braunii) both established in 2012 and festulolium renewed in 2018. Annual yield production, five-year changes in soil C stock, and ecosystem CO2 fluxes in 2020 are documented. The first five-year field observations showed that festulolium produced 76% more biomass as compared to triticale (grain and straw). Meanwhile, there was an increasing trend of soil C stock in festulolium but a declining trend of soil C stock in triticale across the first five years, despite both changes were statistically non-significant. By having measurements of the complete carbon balance for 2020, we can investigate the carbon cycling of a cereal and a perennial grass crop. The results improve our knowledge in how we can optimize the biomass, yield and carbon stocks. Keywords: continuous monoculture; perennial grass; biomass production; soil carbon content; ecosystem CO2 flux

Production of a broad spectrum of products from biomass is of key importance for an economically viable and sustainable biorefinery sector. The aim of this study was to determine the total crude protein yield and theoretical extractable true protein of potential biorefinery feedstocks optimized for supplying biomass to biorefineries. Field experiments during 2013–2014 with perennial crops (pure grasses: cocksfoot, festulolium, reed canary, tall fescue, two miscanthus species and two grass-legume mixtures) and annual crops in optimized rotations (winter rye, sugar beet, maize, triticale, hemp and grass-clover) were compared to traditional crops common in Danish agriculture (maize, barley, wheat and triticale). Theoretical extractable true protein was determined according to the Cornell Net Carbohydrate and Protein System, which fractionates the crude protein based on solubilities. The easily extractable fraction of the true protein was denoted as neutral-extractable. Concentration of crude protein was on average 164–191 g kg−1 DM per cut of pure grasses and grass-legume mixtures, with the summer cuts having the lowest values. Pure grasses produced the highest crude protein yield per hectare annually, ranging from 2595 to 3693 kg ha−1 irrespective of the year, of which 920–1640 kg ha−1 was neutral-extractable protein. Whilst the neutral-extractable true protein per hectare of festulolium and tall fescue was superior to those of all other crops, the neutral extractable true protein per hectare of grass-legume mixtures and of winter rye and maize double crop was similar to those of reed canary and cocksfoot. On a mass basis, 34–46% of crude protein in pure grasses was neutral-extractable, depending on the year. The potential extractability of crude protein may be increased by 14–35% if the cell wall-bound protein can be extracted too.

This study was designed to show the effects of harvest time and frequency on biomass nutrient concentrations (total ash, N, P, K, Ca, Mg, Fe, Mn, Cu and Zn) as well as total nutrient removal potential by festulolium and tall fescue cultivated on a nutrient-rich fen peatland. The harvest managements included a three-cut (3C) and three two-cut (2C) systems which differed by two-week delays of first cut as: 2C-early, 2C-mid and 2C-late, representing phenological stages of pre-heading, inflorescence emergence, and flowering, respectively. In the study year, the grasses received 80-16–60 kg N-P-K ha−1 in spring and 80-0–100 kg N-P-K ha−1 after each harvest (except final). Nutrient concentrations and total ash content in the biomass dropped sharply during spring-summer growth. Concentrations of Ca, Mg and Mn were significantly higher in tall fescue biomass during spring-summer growth, but for other nutrients, there were no consistent differences between the two grasses. Total ash in the biomass from 3C managements (1.1 Mg ha−1) was ∼28% higher than in the biomass removed by 2C managements (0.8 Mg ha−1). Similarly, mean annual N removal by 3C (315 kg N ha−1) was 31% higher than by 2C (240 kg N ha−1) managements, but net removals (removed minus applied N) from both managements were similar (75–80 kg ha−1). Net P-removal by 3C (37 kg P ha−1) was higher than by 2C (26 kg P ha−1) managements, whereas total K removals in all managements were close to the applied K amount (i.e., net removals were close to zero). Whereas all crop/management combinations extracted more N and P than applied, the 2C-late approach is recommended since the biomass yield was higher than for the other 2C approaches, and it required less fertilizer and management inputs than the 3C approach.

To meet the growing challenges for food security, renewable resource production and climate change adaptation, optimized crop rotations (OCRs) should aim to maximize biomass production and export from the field while minimizing carbon (C) and nitrogen (N) footprints. However, the effects of OCRs on aboveground biomass production and soil C and N stock as well as the potential links between them remain poorly understood. In this study in Denmark, we harvested all aboveground biomass and simultaneously investigated soil C and N content and stock in two continuous monocultures (CMs) as well as in four OCRs. Across five-year continuous observations, OCRs significantly increased cumulative aboveground biomass production by 23% compared to CMs. There was no significant difference between OCRs and CMs in soil C and N content in any of the soil layers (0–20, 20–50, and 50–100 cm) after the five years. Moreover, OCRs had no effect on top layer soil C and N stock compared to CMs, even when examined by equivalent soil mass. Slight reductions in soil C and N stock after five years in both OCRs and CMs did not relate to the changes in aboveground biomass production. Our results highlight that it is feasible to produce more biomass for biorefineries in OCRs than in CMs and the reductions in soil C and N stock over time seem similar for the two systems. Longer-term continuous observations are called for to underpin these results.

Climate warming affects soil carbon (C) dynamics, with possible serious consequences for soil C stocks and atmospheric CO2 concentrations. However, the mechanisms underlying changes in soil C storage are not well understood, hampering long-term predictions of climate C-feedbacks. The activity of the extracellular enzymes ligninase and cellulase can be used to track changes in the predominant C sources of soil microbes and can thus provide mechanistic insights into soil C loss pathways. Here we show, using meta-analysis, that reductions in soil C stocks with warming are associated with increased ratios of ligninase to cellulase activity. Furthermore, whereas long-term (≥5 years) warming reduced the soil recalcitrant C pool by 14%, short-term warming had no significant effect. Together, these results suggest that warming stimulates microbial utilization of recalcitrant C pools, possibly exacerbating long-term climate-C feedbacks.

Rewetted peatlands are weak to negligible sources of the greenhouse gas nitrous oxide (N2O). However, rewetted peatlands in use for paludiculture may require nitrogen (N) fertilization potentially creating hot moments for denitrification and N2O emissions. In this study, we measured N2O emissions from an N-rich riparian fen for two consecutive years using static chambers. The field experiment included side-by-side plots cultivated with reed canary grass (Phalaris arundinacea L.) under different degrees of manipulated rewetting. The treatments were defined as control, semi-flooded and flooded conditions corresponding to 2-year weighted mean groundwater table (GWT) depths of 9, 3 and 1 cm below soil surface, respectively. The crop was fertilized and harvested twice a year (160 kg N ha−1 year−1 in two equal splits). Large N2O emissions were observed from all treatments after each fertilization event, which contributed to cumulative annual emissions of 3.2–6.0 kg N2O–N ha−1 in the first year and 1.8–4.2 kg N2O–N ha−1 in the second year. Emissions outside the fertilization periods were negligible. Annual N2O emissions were similar (P > 0.05) among the treatments in the first year whereas control treatments had the lowest emissions in the second year. Nitrogen removal in harvested biomass (197–218 kg N ha−1 year−1) exceeded the fertilizer N in all treatments, indicating that the cultivated biomass utilized substantial amounts of mineralized N from the peat soil. Overall, the results indicate that fertilizer-induced N2O emissions can be high although background soil emissions are low when high GWT is maintained on N-rich riparian peatland.

Rewetting agricultural peatland abates carbon dioxide (CO2) emission, but the resulting waterlogged anaerobic soil condition may create hotspots of methane (CH4) emissions. In this study, we measured CH4 emissions from side-by-side replicated plots in an agricultural fen cultivated with reed canary grass under a control and two experimental rewetting (i.e., paludiculture) conditions as either continuously flooded to soil surface or semi-flooded where water from the flooded plots intruded from sub-surface. Fluxes were measured for two successive years at 1–2 week intervals (total 59 measurement dates) using static chambers. Annual emissions were estimated by trapezoidal linear interpolation of the measured fluxes between the measurement dates. Two-year time-weighted average ground water tables (GWT) in the flooded, semi-flooded and control plots were 1, 3 and 9 cm below soil surface, respectively. The annual average emissions from flooded plots were 82 and 116 g CH4 m−2 yr−1 in Year 1 and 2, respectively, which were significantly higher than the emissions from semi-flooded plots (35 and 69 g CH4 m−2 yr−1 in Year 1 and 2, respectively) and from control plots (3 and 9 g CH4 m−2 yr−1 in Year 1 and 2, respectively). Overall, the results showed that the GWT in paludiculture should be maintained few cm below soil surface during high temperature periods to prevent risks of high CH4 emissions.

Cultivated peatlands under drainage practices contribute significant carbon losses from agricultural sector in the Nordic countries. In this research, we developed the BASGRA-BGC model coupled with hydrological, soil carbon decomposition and methane modules to simulate the dynamic of water table level (WTL), carbon dioxide (CO2) and methane (CH4) emissions for cultivated peatlands. The field measurements from four experimental sites in Finland, Denmark and Norway were used to validate the predictive skills of this novel model under different WTL management practices, climatic conditions and soil properties. Compared with daily observations, the model performed well in terms of RMSE (Root Mean Square Error; 0.06–0.11 m, 1.22–2.43 gC/m2/day, and 0.002–0.330 kgC/ha/day for WTL, CO2 and CH4, respectively), NRMSE (Normalized Root Mean Square Error; 10.3–18.3%, 13.0–18.6%, 15.3–21.9%) and Pearson's r (Pearson correlation coefficient; 0.60–0.91, 0.76–0.88, 0.33–0.80). The daily/seasonal variabilities were therefore captured and the aggregated results corresponded well with annual estimations. We further provided an example on the model's potential use in improving the WTL management to mitigate CO2 and CH4 emissions while maintaining grass production. At all study sites, the simulated WTLs and carbon decomposition rates showed a significant negative correlation. Therefore, controlling WTL could effectively reduce carbon losses. However, given the highly diverse carbon decomposition rates within individual WTLs, adding indicators (e.g. soil moisture and peat quality) would improve our capacity to assess the effectiveness of specific mitigation practices such as WTL control and rewetting.

Compared with annual crops, dedicated perennial bioenergy crops are ascribed additional benefits in terms of reduced greenhouse gas emissions; these benefits include increased carbon (C) storage in soil. We measured Miscanthus-derived C in rhizomes, roots, and 0–100 cm soil beneath three 16-yr-old stands established on sandy soils at two experimental sites in Denmark. Miscanthus C in soil was estimated from changes in the natural abundance of 13C. In the 0–20 cm depth, soil C derived from Miscanthus made up to 15–18% of the soil total C. In the 20–50 cm and 50–100 cm depth, Miscanthus C accounted for less than 7% and 5% of the soil total C, respectively. After 16 yr, the total quantity of Miscanthus C in 0–20 cm ranged from 11.9 to 18.2 Mg C ha−1, of which 23–34% was in rhizomes and roots, substantiating their crucial contribution to soil C storage. Future studies should prioritize the seasonal and annual dynamics of C stored in rhizomes and roots, and the fate of these C pools following termination of Miscanthus stands.

One of the shortcomings of closed chamber methods for soil respiration (SR) measurements is the decreased CO 2 diffusion rate from soil to chamber headspace that may occur due to increased chamber CO 2 concentrations. This feedback on diffusion rate may lead to underestimation of pre-deployment fluxes by linear regression techniques. Thus, usually the cumulative flux curve becomes downward concave due to the decreased gas diffusion rate. Non-linear models based on biophysical theory usually fit to such curvatures and may reduce the underestimation of fluxes. In this study, we examined the effect of increasing chamber enclosure time on SR flux rates calculated using a linear, an exponential and a revised Hutchinson and Mosier model (HMR). Soil respiration rates were measured with a closed chamber in combination with an infrared gas analyzer. During SR flux measurements the chamber was placed on fixed collars, and CO 2 concentration in the chamber headspace were recorded at 1-s intervals for 45 min. Fluxes were measured in different soil types (sandy, sandy loam and organic soils), and for various manipulations (tillage, rain and drought) and soil conditions (temperature and moisture) to obtain a range of fluxes with different shapes of flux curves. The linear method provided more stable flux results during short enclosure times (few min) but underestimated initial fluxes by 15–300% after 45 min deployment time. Non-linear models reduced the underestimation as average underestimation was only about 10% after 45 min for regular flux curves. For irregular flux curves with a rapid increase in CO 2 concentration immediately after chamber deployment it was shown that short enclosure times were prone to overestimation of pre-deployment fluxes, but this was mitigated by longer enclosure times (>10–15 min).

Background and Aims The C4 perennial grass miscanthus has been found to be less sensitive to cold than most other C4 species, but still emerges later in spring than C3 species. Genotypic differences in miscanthus were investigated to identify genotypes with a high cold tolerance at low temperatures and quick recovery upon rising temperatures to enable them to exploit the early growing season in maritime cold climates. Suitable methods for field screening of cold tolerance in miscanthus were also identified.Methods Fourteen genotypes of M. sacchariflorus, M. sinensis, M. tinctorius and M. × giganteus were selected and grown under warm (24 °C) and cold (14 °C) conditions in a controlled environment. Dark-adapted chlorophyll fluorescence, specific leaf area (SLA) and net photosynthetic rate at a photosynthetically active radiation (PAR) of 1000 μmol m–2 s–1 (A1000) were measured. Photosynthetic light and CO2 response curves were obtained from 11 of the genotypes, and shoot growth rate was measured under field conditions.Key Results A positive linear relationship was found between SLA and light-saturated photosynthesis (Asat) across genotypes, and also between shoot growth rate under cool field conditions and A1000 at 14 °C in a climate chamber. When lowering the temperature from 24 to 14 °C, one M. sacchariflorus exhibited significantly higher Asat and maximum photosynthetic rate in the CO2 response curve (Vmax) than other genotypes at 14 °C, except M. × giganteus ‘Hornum’. Several genotypes returned to their pre-chilling A1000 values when the temperature was increased to 24 °C after 24 d growth at 14 °C.Conclusions One M. sacchariflorus genotype had similar or higher photosynthetic capacity than M. × giganteus, and may be used for cultivation together with M. × giganteus or for breeding new interspecies hybrids with improved traits for temperate climates. Two easily measured variables, SLA and shoot growth rate, may be useful for genotype screening of productivity and cold tolerance.

High-yielding perennial grass can, when compared to classical grain crop production, considerably increase biomass yields per unit area in Northern European agriculture, which is important to meet the demand for biomass in a growing bioeconomy. Potential benefits for the carbon footprint will, however, depend on greenhouse gas (GHG) emissions during the entire biomass production cycle, which includes grassland renovation at regular intervals to maintain high biomass yields. The renovation phase may accelerate nitrous oxide (N2O) emissions associated with residue decomposition. This study examined the effect of renovating a six-year old festulolium (x Festulolium braunii L.) crop on N2O emissions. As a secondary objective, the study evaluated the potential for mitigating N2O emissions in spring by spraying the sward with a nitrification inhibitor containing 3,4-dimethylpyrazole phosphate (DMPP) prior to cultivation. A replicated split-plot design was used, where one half of each main plot was rotovated and seeded with spring barley (Hordeum vulgare L.) as a catch crop during spring, followed by ploughing and reseeding of festulolium in the autumn. In the other half of each main plot, festulolium was left without cultivation as reference. Four subplots were defined within both cultivated plots and reference plots with (“+DMPP”) or without (“−DMPP”) DMPP spraying of festulolium before cultivation, and with (“F”) or without (“NF”) fertilisation with 119, 425 and 50 kg N ha−1 in spring barley, festulolium and re-established festulolium, respectively. All four combinations of DMPP treatment and fertilisation were represented, i.e., F+DMPP, F-DMPP, NF+DMPP and NF-DMPP. Monitoring of N2O emissions occurred in two periods, April–June (“spring”) and August-October (“autumn”). In the autumn, where festulolium was reestablished, N2O emissions were only monitored in the plots without DMPP treatment in spring, since potential legacy effects of DMPP were not part of this study. Cultivation increased N2O emissions 2.5-fold in spring, and 2-fold in autumn, compared to uncultivated plots. The N2O emissions induced by fertilisation were similar from cultivated and reference plots, and emission factors for spring barley (Apr–Jun), re-sown festulolium (Aug–Oct) and uncultivated festulolium (reference, Apr-Oct) during the monitoring periods were, respectively, 0.40, 0.42 and 0.12%. Spraying festulolium with DMPP delayed the transformation of ammonium to nitrate during spring. DMPP did not reduce N2O emissions significantly in this study. In contrast, there was an apparent interaction between decomposing residues and mineral fertiliser with respect to emissions of N2O, which is a potential GHG mitigation target.

Cultivation of bioenergy crops in rewetted peatland (paludiculture) is considered as a possible land use option to mitigate greenhouse gas (GHG) emissions. However, bioenergy crops like reed canary grass (RCG) can have a complex influence on GHG fluxes. Here we determined the effect of RCG cultivation on GHG emission from peatland rewetted to various extents. Mesocosms were manipulated to three different ground water levels (GWLs), i.e. 0, −10 and −20 cm below the soil surface in a controlled semi-field facility. Emissions of CO2 (ecosystem respiration, ER), CH4 and N2O from mesocosms with RCG and bare soil were measured at weekly to fortnightly intervals with static chamber techniques for a period of 1 year. Cultivation of RCG increased both ER and CH4 emissions, but decreased the N2O emissions. The presence of RCG gave rise to 69, 75 and 85% of total ER at −20, −10 and 0 cm GWL, respectively. However, this difference was due to decreased soil respiration at the rising GWL as the plant-derived CO2 flux was similar at all three GWLs. For methane, 70–95% of the total emission was due to presence of RCG, with the highest contribution at −20 cm GWL. In contrast, cultivation of RCG decreased N2O emission by 33–86% with the major reductions at −10 and −20 cm GWL. In terms of global warming potential, the increase in CH4 emissions due to RCG cultivation was more than offset by the decrease in N2O emissions at −10 and −20 cm GWL; at 0 cm GWL the CH4 emissions was offset only by 23%. CO2 emissions from ER were obviously the dominant RCG-derived GHG flux, but above-ground biomass yields, and preliminary measurements of gross photosynthetic production, showed that ER could be more than balanced due to the photosynthetic uptake of CO2 by RCG. Our results support that RCG cultivation could be a good land use option in terms of mitigating GHG emission from rewetted peatlands, potentially turning these ecosystems into a sink of atmospheric CO2.

Willow (Salix spp.) is expected to contribute significantly to the woody bioenergy system in the future, so more information on how to sample the quality of the willow biomass is needed. The objectives of this study were to investigate the spatial variation of elements within shoots of a willow clone ‘Tordis’, and to reveal the relationship between sampling position, shoot diameters, and distribution of elements. Five Tordis willow shoots were cut into 10–50 cm sections from base to top. The ash content and concentration of twelve elements (Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, P, Si, and Zn) in each section were determined. The results showed large spatial variation in the distribution of most elements along the length of the willow shoots. Concentrations of elements in 2-year old shoots of the willow clone Tordis were fairly stable within the range of 100–285 cm above ground and resembled the mean concentration of the whole stem (from 86% to 108%, except for Mg, Na, Al and Fe). For practical reasons it is recommended to sample 10 cm sections at the breast height (125–135 cm) to minimise labour costs. Willow (Salix spp.) is expected to contribute significantly to the woody bioenergy system in the future, so more information on how to sample the quality of the willow biomass is needed. The objectives of this study were to investigate the spatial variation of elements within shoots of a willow clone ‘Tordis’, and to reveal the relationship between sampling position, shoot diameters, and distribution of elements. Five Tordis willow shoots were cut into 10–50 cm sections from base to top. The ash content and concentration of twelve elements (Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, P, Si, and Zn) in each section were determined. The results showed large spatial variation in the distribution of most elements along the length of the willow shoots. Concentrations of elements in 2-year old shoots of the willow clone Tordis were fairly stable within the range of 100–285 cm above ground and resembled the mean concentration of the whole stem (from 86% to 108%, except for Mg, Na, Al and Fe). For practical reasons it is recommended to sample 10 cm sections at the breast height (125–135 cm) to minimise labour costs.

This study evaluated the effects of harvesting managements with two-cuts (2C) and three-cuts (3C) per year for subsequent specific methane yield (SMY) and methane yield per hectare (MYPH) of festulolium and tall fescue cultivated on a riparian fen peatland in a block-designed field experiment (n = 3). For the 2C managements, three timings of the first cut were implemented corresponding to growth stages of pre-heading (2C-early), inflorescence emergence (2C-mid), and flowering (2C-late). Anaerobic digestion batch assays with biomass samples were run for 68 days, showing that 90% of total methane (CH4) was produced within 38 days. Specific methane yield ranged from 315 to 464 NL CH4 kg−1 volatile solids (mean, 393 NL). On average, SMY of the final cut biomass was 13% lower than the first cut biomass. Methane yield per hectare ranged from 5277 to 6963 Nm3 CH4 ha−1 (mean, 6265 Nm3) and was predominantly influenced by biomass yield since SMY only deviated modestly in relation to harvest management (cro...

This study reports the annual carbon balance of a drained riparian fen under two-cut or three-cut managements of festulolium and tall fescue. CO2 fluxes measured with closed chambers were partitioned into gross primary production (GPP) and ecosystem respiration (ER) for modelling according to environmental factors (light and temperature) and canopy reflectance (ratio vegetation index, RVI). Methodological assessments were made of (i) GPP models with or without temperature functions (Ft) to adjust GPP constraints imposed by low temperature (

The fuel quality was assessed for nine poplar clones (AF2, Androscoggin, Max1, Max3, Max4, Monviso, Muhle-Larsen, NE42, Weser6) and one willow clone (Inger) grown as short rotation coppice (SRC) on four sites in the Brandenburg area in Germany. Fuel quality was analysed in 3-year old shoots in terms of dry matter (DM) mass fraction, total ash mass fraction and concentration of 14 ash-related elements (Al, Ca, Cd, Cl, Cu, Fe, K, Mg, Mn, Na, P, S, Si, Zn). Clone significantly affected DM and ash mass fraction and concentration of 11 of the 14 elements, site affected concentration of 7 elements, and clone and site interacted on DM, ash mass fraction and concentration of 7 elements. Among the poplar clones, Androscoggin and NE42 generally exhibited highest quality with higher DM mass fraction and lower concentrations of ash, Ca, K, P, Cd and Cu than other poplar clones. The willow clone had high DM mass fraction, low ash mass fraction and generally low concentrations of the major ash-forming elements compared to poplar clones. However, willow had significantly higher mean concentration of Cd, Mn and Zn than all poplar clones but with significant clone-site interactions and, on some sites, the concentrations were no higher in willow than in the poplar clones. Shoot diameter significantly affected fuel quality with thin shoots generally having higher ash mass fraction and element concentrations than thicker shoots. In conclusion, fuel quality of SRC biomass may be improved by selecting appropriate clones and by increasing shoot diameter at harvest.

Eight willow (Salix) clones (Inger, Klara, Linnea, Resolution, Stina, Terra Nova, Tora, Tordis) were planted on two soil types in Denmark. The biomass quality was evaluated after 3 years of growth by measuring differences in concentrations of 14 elements associated with ash behavior during combustion, and total ash content. Three-year-old shoots of Tordis and Tora performed in general the best with relatively lower mean concentrations of K, Ca, Na, S, and total ash content than other clones across the two experimental sites. Terra Nova was the least suited for combustion as it contained up to 22, 27, 35, and 23 % higher concentrations of K, S, Ca, and total ash than the other clones. In addition to clone and site, appropriate management could further improve the fuel quality of willow biomass. When shoots of Inger were harvested annually (1-year shoots) high concentrations of K and Cl were found in all three consecutive harvests, but concentrations decreased significantly when rotation length was extended beyond 1 year of growth. Significant decreases of Mg, Na, P, S, and Zn were also registered from 2- to 3-year-old shoots. No difference in quality of biomass was found between two plant densities (8000 and 12,000 trees ha−1) of the clones Inger and Tora after the first 3-year rotation when grown at the site with a coarse sandy soil. The study indicates considerable diversity in concentration of elements within commercially available willow cultivars and suggests breeders and growers to select clones not only according to biomass yield potential but also according to biomass quality. Eight willow (Salix) clones (Inger, Klara, Linnea, Resolution, Stina, Terra Nova, Tora, Tordis) were planted on two soil types in Denmark. The biomass quality was evaluated after 3 years of growth by measuring differences in concentrations of 14 elements associated with ash behavior during combustion, and total ash content. Three-year-old shoots of Tordis and Tora performed in general the best with relatively lower mean concentrations of K, Ca, Na, S, and total ash content than other clones across the two experimental sites. Terra Nova was the least suited for combustion as it contained up to 22, 27, 35, and 23 % higher concentrations of K, S, Ca, and total ash than the other clones. In addition to clone and site, appropriate management could further improve the fuel quality of willow biomass. When shoots of Inger were harvested annually (1-year shoots) high concentrations of K and Cl were found in all three consecutive harvests, but concentrations decreased significantly when rotation length was extended beyond 1 year of growth. Significant decreases of Mg, Na, P, S, and Zn were also registered from 2- to 3-year-old shoots. No difference in quality of biomass was found between two plant densities (8000 and 12,000 trees ha−1) of the clones Inger and Tora after the first 3-year rotation when grown at the site with a coarse sandy soil. The study indicates considerable diversity in concentration of elements within commercially available willow cultivars and suggests breeders and growers to select clones not only according to biomass yield potential but also according to biomass quality.

Optimal fertilization of short rotation coppice (SRC) willow is important both in terms of economic yield and environmental effect. We measured biomass yield and nutrient uptake in two willow clones, Inger and Tordis, grown on a coarse sandy soil and within six different fertilization regimes. Fertilization treatments were carried out during two two-year harvest rotations, beginning in the 2nd growth year of the plantation. Willow was fertilized as follows with names referring to type of fertilizer and total quantities of nitrogen (kg ha −1 ) in first and second year within both rotations: 1) Control 0+0 , 2) NPK 120+0 , 3) Slurry 180+0 , 4) NPK 120+120 , 5) NPK 240+0 , 6) Slurry 360+0 . Fertilization affected biomass yield significantly but interacted with rotation and clone. In first rotation, fertilization increased dry matter (DM) yield across clones significantly from 3.7 Mg ha −1 y −1 for Control 0+0 to 6.5, 6.4 and 5.6 for Slurry 360+0 , NPK 120+120 and NPK 240+0 , respectively. In second rotation, yield increased from 6.2 Mg ha −1 y −1 to 8.8, 8.2, 7.8 and 7.4 for Slurry 360+0 , NPK 240+0 , Slurry 180+0 and NPK 120+120 , respectively. Biomass dry matter yield per ha increased linearly at 15 kg kg −1 of applied total-N in both rotations. The yield increase in response to fertilization was generally larger in Inger than in Tordis. In general, element concentration in the harvested biomass was either unaffected or slightly reduced by fertilization. In conclusion, yield response to fertilization appears to be primarily related to the quantity of N applied but the effect depended on fertilizer type, harvest rotation and willow clone.

Rewetting of drained peatlands has been recommended to reduce CO2 emissions and to restore the carbon sink function of peatlands. Recently, the combination of rewetting and biomass production (paludiculture) has gained interest as a possible land use option in peatlands for obtaining such benefits of lower CO2 emissions without losing agricultural land. The present study quantified the carbon balance (CO2, CH4 and harvested biomass C) of rewetted and drained peat soils under intensively managed reed canary grass (RCG) cultivation. Mesocosms were maintained at five different ground water levels (GWL), i.e., 0, 10, 20 cm below the soil surface, representing rewetted peat soils, and 30 and 40 cm below the soil surface, representing drained peat soils. Net ecosystem exchange (NEE) of CO2 and CH4 emissions were measured during the growing period of RCG (May to September) using transparent and opaque closed chamber methods. The average dry biomass yield was significantly lower from rewetted peat soils (12 Mg ha−1) than drained peat soils (15 Mg ha−1). Also, CO2 fluxes of gross primary production (GPP) and ecosystem respiration (ER) from rewetted peat soils were significantly lower than drained peat soils but net uptake of CO2 was higher from rewetted peat soils. Cumulative CH4 emissions were negligible (0.01 g CH4 m−2) from drained peat soils but were significantly higher (4.9 g CH4 m−2) from rewetted peat soils during measurement period (01 May-15 September, 2013). The extrapolated annual C balance was 0.03 and 0.68 kg C m−2 from rewetted and drained peat soils, respectively indicating that rewetting and paludiculture can reduce the loss of carbon from peatlands.

Production of energy crops is promoted as a means to mitigate global warming by decreasing dependency on fossil energy. However, agricultural production of bioenergy can have various environmental effects depending on the crop and production system. In a field trial initiated in 2008, nitrate concentration in soil water was measured below winter wheat, grass-clover and willow during three growing seasons. Crop water balances were modelled to estimate the amount of nitrate leached per hectare. Additionally, dry matter yields and nitrogen (N) yields were measured, and N balances and energy balances were calculated.In willow, nitrate concentrations were up to approx. 20 mg L−1 nitrate-N during the establishment year but declined subsequently to less than 5 mg L−1 nitrate-N, resulting in an annual N leaching loss of 18, 3 and 0.3 kg ha−1 year−1 N in the first three years after planting, respectively. A similar trend was observed in grass-clover where concentrations stabilized at 2 to 4 mg L−1 nitrate-N from the beginning of the second growing season, corresponding to leaching of approximately 5 kg ha−1 year−1 N. In winter wheat, an annual N leaching loss of 36 to 68 kg ha−1 year−1 was observed. For comparison, nitrate leaching was also measured in an old willow crop established in 1996 from which N leaching ranged from 6 to 27 kg ha−1 year−1. Dry matter yields ranged between 5.9 and 14.8 Mg year−1 with lowest yield in the newly established willow and the highest yield harvested in grass-clover. Grass-clover gave the highest net energy yield of 244 GJ ha−1 year−1 whereas old willow, winter wheat and first rotation willow gave net energy yields of 235, 180 and 105 GJ ha−1 year−1. The study showed that perennial crops can provide high energy yields and significantly reduce N losses compared to annual crops. Production of energy crops is promoted as a means to mitigate global warming by decreasing dependency on fossil energy. However, agricultural production of bioenergy can have various environmental effects depending on the crop and production system. In a field trial initiated in 2008, nitrate concentration in soil water was measured below winter wheat, grass-clover and willow during three growing seasons. Crop water balances were modelled to estimate the amount of nitrate leached per hectare. In addition, dry matter yields and nitrogen (N) yields were measured, and N balances and energy balances were calculated. In willow, nitrate concentrations were up to approximately 20 mg l−1 nitrate-N during the establishment year, but declined subsequently to

Two potato (Solanum tuberosum) cultivars, Dali and Oleva, with, respectively, low and high susceptibility to blackspot bruise, were grown in 1998 and 1999. Tubers from plants of Dali and Oleva were harvested three and four times during the final growth period, respectively. The tubers were analysed for blackspot susceptibility and colour of blackspots four times during storage and the tuber cortices were analysed for discolouration potential, activity of polyphenol oxidase (PPO) and concentration of PPO substrates (free tyrosine, chlorogenic acid, caffeic acid). During tuber growth, an increasing abundance of red- and yellow-coloured intermediates and final black-coloured compounds in the assay of potential discolouration were observed. The overall correlation coefficients (r) between red intermediates and free tyrosine were 0.74 and 0.64 for Dali and Oleva, respectively, whereas they were 0.49 and 0.68, respectively, between yellow intermediates and free tyrosine. The overall correlation coefficients between black end-products and free tyrosine were 0.69 and 0.67 for Dali and Oleva, respectively. No overall correlation was found between the discolouration potential and other phenols. Changes in blackspot susceptibility and in colour of blackspots during growth and storage of the tubers could not be ascribed to changes in the discolouration potential (colour development of blended tuber tissue), PPO activity or concentration of phenols in the tuber cortices. Contrary to the discolouration potential, the blackspots were significantly darker at the beginning of the storage period compared to later in storage. Furthermore, during tuber growth the stable colour of bruises did not reflect the concomitant increase in discolouration potential. The results provide supporting evidence that intracellular compartmentation is the determining factor for blackspot bruise susceptibility in potato tubers.

Organic soils are a main source of direct nitrous oxide (N2O) emissions, an important greenhouse gas (GHG). Observed N2O emissions from organic soils are highly variable in space and time which causes high uncertainties in national emission inventories. Those uncertainties could be reduced when relating the upscaling process to a priori identified key drivers by using available N2O observations from plot scale in empirical approaches. We used the empirical fuzzy modelling approach MODE to identify main drivers for N2O and utilize them to predict the spatial emission pattern of European organic soils. We conducted a meta study with a total amount of 659 annual N2O measurements which was used to derive separate models for different land use types. We applied our models to available, spatial explicit input driver maps to upscale N2O emissions on European level and compared the inventory with recently published IPCC emission factors. The final statistical models explained up to 60% of the N2O variance. Our study results showed that cropland and grasslands emitted the highest N2O fluxes 0.98 ± 1.08 and 0.58 ± 1.03 g N2O-N m−2 a−1, respectively. High fluxes from cropland sites were mainly controlled by low soil pH-value and deep drained groundwater tables. Grassland hotspot emissions were strongly related to high amount of N-fertilizer inputs and warmer winter temperatures. In contrast N2O fluxes from natural peatlands were predominantly low (0.07±0.27 g N2O-N m−2 a−1) and we found no relationship with the tested drivers. The total inventory for direct N2O emissions from organic soils in Europe amount up to 149.5 Gg N2O-N a−1, which included also fluxes from forest and peat extraction sites and exceeds the inventory calculated by IPCC emission factors of 87.4 Gg N2O-N a−1. N2O emissions from organic soils represent up to 13% of total European N2O emissions reported in the European Union (EU) greenhouse gas inventory of 2011 from only 7% of the EU area. Thereby the model demonstrated that with up to 85% the major part of the inventory is induced by anthropogenic management, which shows the significant reduction potential by rewetting and extensivation of agricultural used peat soils.

Tubers of the potato cultivar Maris Piper (MP) were grown in 1996 and stored for 8 months, whereas tubers of the cultivar Colmo (CM) were grown in 1997 and harvested immature. In a timecourse study the two cultivars, which had two distinct physiological ages, were investigated for blackspot susceptibility in relation to cellular integrity. Tubers were equilibrated at 5 °C and struck by a falling bolt. The site of impact was analysed for cation efflux from tuber half-discs and enzymatic activity of polyphenoloxidase (PPO), lipoxygenase (LOX), ascorbate peroxidase (APX) and catalase after 0, 1, 2, 4, 8, 16 and 32 h of tuber incubation. Tubers of MP were 10 times more blackspot-susceptible than those of CM. The membranes of MP leaked more K+, Mg2+ and Ca2+ than those of CM. Both cultivars showed a very fast increase in K+ leakage immediately after impact. Thereafter, CM seemed to reconstitute the membranes, while high efflux of K+ from MP continued for up to 32 h of incubation. Mg2+ efflux from MP increased and peaked 8 h after impact, but no effect was found on CM. Ca2+ and Na+ effluxes were not influenced by the impact. More than twice the activity of LOX and more than three times the activity of PPO were found in CM compared to MP, but little effect of impact was registered. The activity of APX was higher in MP than in CM, and again little effect of impact was found. Little effect of impact on catalase activity was found and the level of catalase activity was similar in both cultivars. © 2000 Society of Chemical Industry

Background and aimsCombination of rewetting and wetland crop cultivation (paludiculture) is pursued as a wider carbon dioxide (CO2) mitigation option in drained peatland. However, information on the overall greenhouse gas (GHG) balance for paludiculture is lacking. We investigated the GHG balance of peatlands grown with reed canary grass (RCG) and rewetted to various extents.MethodsGas fluxes of CO2, methane (CH4) and nitrous oxide (N2O) were measured with a static chamber technique for 10 months from mesocosms sown with RCG and manipulated to ground water levels (GWL) of 0, −10, −20, −30 and −40 cm below the soil surface. Gross primary production (GPP) was estimated from the above ground biomass yield.ResultsThe mean dry biomass yield across all water table treatments was 6 Mg ha−1 with no significant differences between the treatments. Raising the GWL to the surface decreased both the net ecosystem exchange (NEE) of CO2 and N2O emissions whereas CH4 emissions increased. Total cumulative GHG emissions (for 10 months) corresponded to 0.08, 0.13, 0.61, 0.68 and 0.98 kg CO2 equivalents m−2 from the GWL treatments at 0, −10, −20, −30 and −40 cm below the soil surface, respectively.ConclusionsThe results showed that a reduction in total GHG emission can be achieved without losing the productivity of newly established RCG when GWL is maintained close to the surface. Further studies should address the practical constrains and long-term productivity of RCG cultivation in rewetted peatlands. Background and aimsCombination of rewetting and wetland crop cultivation (paludiculture) is pursued as a wider carbon dioxide (CO2) mitigation option in drained peatland. However, information on the overall greenhouse gas (GHG) balance for paludiculture is lacking. We investigated the GHG balance of peatlands grown with reed canary grass (RCG) and rewetted to various extents.MethodsGas fluxes of CO2, methane (CH4) and nitrous oxide (N2O) were measured with a static chamber technique for 10 months from mesocosms sown with RCG and manipulated to ground water levels (GWL) of 0, −10, −20, −30 and −40 cm below the soil surface. Gross primary production (GPP) was estimated from the above ground biomass yield.ResultsThe mean dry biomass yield across all water table treatments was 6 Mg ha−1 with no significant differences between the treatments. Raising the GWL to the surface decreased both the net ecosystem exchange (NEE) of CO2 and N2O emissions whereas CH4 emissions increased. Total cumulative GHG emissions (for 10 months) corresponded to 0.08, 0.13, 0.61, 0.68 and 0.98 kg CO2 equivalents m−2 from the GWL treatments at 0, −10, −20, −30 and −40 cm below the soil surface, respectively.ConclusionsThe results showed that a reduction in total GHG emission can be achieved without losing the productivity of newly established RCG when GWL is maintained close to the surface. Further studies should address the practical constrains and long-term productivity of RCG cultivation in rewetted peatlands.

A rapid method is needed to assess biogas and methane yield potential of various kinds of substrate prior to anaerobic digestion. This study reports near infrared reflectance spectroscopy (NIRS) as a rapid alternative method to the conventional batch methods for prediction of specific biogas yield (SBY), specific methane yield (SMY) and kinetics of biogas yield (k-SBY) of reed canary grass (RCG) biomass. Dried and powdered RCG biomass with different level of maturity was used for biochemical composition analysis, batch assays and NIRS analysis. Calibration models were developed using partial least square (PLS) regression from NIRS spectra. The calibration models for SBY (R2 = 0.68, RPD = 1.83) and k-SBY (R2 = 0.71, RPD = 1.75) were better than the model for SMY (R2 = 0.53, RPD = 1.49). Although the PLS model for SMY was less successful, the model performance was better compared to the models based on chemical composition. A rapid method is needed to assess biogas and methane yield potential of various kinds of substrate prior to anaerobic digestion. This study reports near infrared reflectance spectroscopy (NIRS) as a rapid alternative method to the conventional batch methods for prediction of specific biogas yield (SBY), specific methane yield (SMY) and kinetics of biogas yield (k-SBY) of reed canary grass (RCG) biomass. Dried and powdered RCG biomass with different level of maturity was used for biochemical composition analysis, batch assays and NIRS analysis. Calibration models were developed using partial least square (PLS) regression from NIRS spectra. The calibration models for SBY (R2 = 0.68, RPD = 1.83) and k-SBY (R2 = 0.71, RPD = 1.75) were better than the model for SMY (R2 = 0.53, RPD = 1.49). Although the PLS model for SMY was less successful, the model performance was better compared to the models based on chemical composition.

This study examined the influence of harvest time on biomass yield, dry matter partitioning, biochemical composition and biological methane potential of reed canary grass harvested twice a month in one-cut (OC) management. The regrowth of biomass harvested in summer was also harvested in autumn as a two-cut management with (TC-F) or without (TC-U) fertilization after summer harvest. The specific methane yields decreased significantly with crop maturity that ranged from 384 to 315 and from 412 to 283 NL (normal litre) (kg VS)−1 for leaf and stem, respectively. Approximately 45% more methane was produced by the TC-F management (5430 Nm3 ha−1) as by the OC management (3735 Nm3 ha−1). Specific methane yield was moderately correlated with the concentrations of fibre components in the biomass. Larger quantity of biogas produced at the beginning of the biogas assay from early harvested biomass was to some extent off-set by lower concentration of methane. -------------------------------------------------------------------------------- This study examined the influence of harvest time on biomass yield, dry matter partitioning, biochemical composition and biological methane potential of reed canary grass harvested twice a month in one-cut (OC) management. The regrowth of biomass harvested in summer was also harvested in autumn as a two-cut management with (TC-F) or without (TC-U) fertilization after summer harvest. The specific methane yields decreased significantly with crop maturity that ranged from 384 to 315 and from 412 to 283 NL (normal litre) (kg VS)-1 for leaf and stem, respectively. Approximately 45% more methane was produced by the TC-F management (5430 Nm3 ha-1) as by the OC management (3735 Nm3 ha-1). Specific methane yield was moderately correlated with the concentrations of fibre components in the biomass. Larger quantity of biogas produced at the beginning of the biogas assay from early harvested biomass was to some extent off-set by lower concentration of methane.

A high content of minerals in biomass feedstock may cause fouling, slagging, and corrosion in the furnace during combustion. Here, a new pressurized microwave digestion method for biomass digestion prior to elemental analysis is presented. This high-throughput method is capable of processing approximately 48 samples per hour with reduced laboratory hazards and waste because only a very small volume of hydrofluoric acid is used. Concentrations of 12 elements (Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, P, Si, and Zn) were determined using inductively coupled plasma–optical emission spectroscopy (ICP–OES). National Institute of Standards and Technology (NIST) standard reference materials (SRMs) 1515 apple leaves and 1575a pine needles were used for method validation. Recoveries of the 12 elements in the NIST SRMs ranged from 93 to 115%. A comparison of the high-throughput method with the European Union (EU) standard method showed agreements in the range from 98 to 115% (except for Al) when the elements were quantified in plant material of the energy crop Miscanthus × giganteus. A high content of minerals in biomass feedstock may cause fouling, slagging, and corrosion in the furnace during combustion. Here, a new pressurized microwave digestion method for biomass digestion prior to elemental analysis is presented. This high-throughput method is capable of processing approximately 48 samples per hour with reduced laboratory hazards and waste because only a very small volume of hydrofluoric acid is used. Concentrations of 12 elements (Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, P, Si, and Zn) were determined using inductively coupled plasma–optical emission spectroscopy (ICP–OES). National Institute of Standards and Technology (NIST) standard reference materials (SRMs) 1515 apple leaves and 1575a pine needles were used for method validation. Recoveries of the 12 elements in the NIST SRMs ranged from 93 to 115%. A comparison of the high-throughput method with the European Union (EU) standard method showed agreements in the range from 98 to 115% (except for Al) when the elements were quantified in plant material of the energy crop Miscanthus × giganteus.

Uptake of various doses (0.27-4.06 g litre-') of glyphosate acid formu- lated with various concentrations (0.27-5.42 g litre-') of two polyethoxylated alcohol surfactants 'Genapol' T-150, 'Genapol' T-250) in wheat (Triticum aesti- uum L. cv. Ralle) 24 h after application was studied. Both surfactants greatly enhanced glyphosate uptake at concentrations up to 1.35 g litre-'. Uptake could be slightly further improved by 'Genapol' T-150 up to 5.42 g litre-' while 'Genapol' T-250 at this high concentration antagonized uptake a little. Uptake of glyphosate-monoammonium formulated with a quaternary ammonium sur- factant ('Trimao' (8PO)) in wheat and white mustard (Sinapis alba L. cv. Alba) was also studied. Uptake of glyphosate-monoammonium in wheat was enhanced at surfactant concentrations up to 1.35 g litre-'. Beyond this concentration uptake continued to increase slightly but not significantly. Generally, glyphosate- monoammonium formulated with 'Trimao' (8PO) was not taken up as exten- sively by mustard as by wheat, and the optimum surfactant concentration is probably higher on mustard. The optimal combinations of surfactant concentra- tion and glyphosate dose based on uptake 24 h after application were used in a time-course study. Results from uptake studies were compared with the efficacy of similar formu- lations on wheat. The surfactant concentration range which gave the most pro- nounced effect on glyphosate uptake was found to be similar (0-1 g litre-I) in both studies. However, the surfactant concentration providing maximum herbi- cide uptake was found to be higher in the uptake study compared to the sur- factant concentration providing optimal efficacy in the dose-response experiments. A dose rate of 0.5 g litre-' of 'Tween' 20 (sorbitan monolaurate surfactant) improved efficacy of a formulation with an optimal mix of glyphosate-monoammonium and 'Trimao' (8PO). Ammonium sulfate (5.0 g litre- ') did not improve this formulation further.

Paludiculture, and in particular the cultivation of perennial grasses as biomass feedstock for green biorefineries, may be an economic and environmentally sustainable option for agricultural peatlands in temperate regions. However, the optimal biomass quality for protein extraction from flood-tolerant grasses is largely unknown. The aim of this study was to define the combined effect of harvest and fertilization frequency, with one to five annual cuts, on protein yield and extractability for the grasses tall fescue (TF) and reed canary grass (RCG), cultivated on an agricultural fen peatland in Denmark.The content of protein fractions was determined according to the Cornell Net Carbohydrate and Protein System (CNCPS). We assessed protein extractability by lab-scale biorefinery techniques using a screw-press followed by acid precipitation of true protein. The two methods were compared to correlate potential extractable protein yields with actual biorefinery outputs. We found the highest annual biomass and crude protein (CP) yields in the two cut treatments, with 13.4 and 15.6 t dry matter (DM) ha−1 year−1, containing 2.9–3.4 t CP ha−1 year−1for TF and RCG, respectively. The highest neutral-extractable (fractions B1and B2) true protein yields of 1.1 and 1.5 t ha−1 year−1were found in the two cut treatments, representing 39% (TF) - 45% (RCG) of total CP. Using biorefining techniques, we were able to precipitate up to 2.2 t DM ha−1 year−1of protein concentrate, containing up to 39% CP. Significant correlations between methods were found, with a distinct relationship between CNCPS fractions B1+ B2and CP yield of the protein concentrate, indicating the suitability of the CNCPS as an indicator for extractable protein yields. Biomass and CP yields were not significantly improved beyond two annual cuts. However, timing and harvest frequencies significantly affected plant maturity and consequently extractable CP contents and protein concentrate yields. We conclude that TF and RCG are promising feedstocks for green biorefineries due to high biomass, extractable CP, and protein concentrate yields, and highlight the potential of flood-tolerant grasses, cultivated on wet agricultural peatlands, for an enhanced valorisation beyond the common utilisation for bioenergy.