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Emerging studies provide promising evidence that applying zeolite combined with water-saving irrigation could effectively retain soil nutrients and increase rice yields. However, the effects of this water-nitrogen management strategy on soil nitrogen (N) loss through leaching and runoff are unclear under field conditions. Herein, we explored the dynamics of N concentrations, quantified soil N losses through leachate and runoff, and investigated the response of reducing N loss on rice yield. A three-year field experiment (2018−2020) was conducted in Donggang city of Liaoning Province in northeast China. The field experiment used a split-plot design, including two irrigation regimes [continuously flooded irrigation (CF) and alternate wetting and drying irrigation (AWD)] as main plots, and two zeolite applications (Z0, no zeolite; Z10, 10 t ha−1 zeolite) as sub-plots, so as to quantify their effects on TN, NH4+-N, NO3−-N loss, and rice yield. Averaged across 3 years, our results showed that AWD reduced the volume of irrigation, leachate, and runoff by 22.2%, 20.8%, and 18.9%, respectively, compared with CF. AWD also decreased the losses of total N (TN), NH4+-N, and NO3−-N by 25.5%, 17.5%, and 11.1% in leachate and by 22.9%, 18.3%, and 26.3% in runoff, respectively, compared with CF. Compared to Z0, Z10 reduced the losses of TN, NH4+-N, and NO3−-N by 16.0%, 16.9%, and 19.4% in leachate and by 10.0%, 14.0%, and 5.9% in runoff, respectively. N output through leaching and runoff under AWD and Z10 was decreased by 2.1% and 2.2%, respectively, compared with CF and Z0. No significant difference was found in rice yield between CF and AWD, whereas rice yields increased 3.3% under Z10 compared with Z0. Altogether, our results highlight that the combination of zeolite and AWD can simultaneously produce more rice yield and reduce soil N losses.

Increasing studies indicate that alternate wetting and drying irrigation (IAWD) can significantly increase water use efficiency in paddy fields, whereas this method may also cause high nitrous oxide (N2O) emissions. Therefore, effective management strategies are urgently required for ameliorating the adverse effect of IAWD on N2O emissions. Zeolite is increasingly used as a potential effective soil conditioner to reduce N2O emissions. However, few studies have been conducted to explore the effect of zeolite on N2O emissions and rice grain yield as well as the associated soil physicochemical properties in paddy fields under IAWD. Here, a two-year field experiment was conducted using lysimeters to assess the effect of two irrigation regimes (ICF: continuously flooded irrigation; IAWD: alternate wetting and drying irrigation) and two zeolite management regimes (ZU: urea alone (non-zeolite control); ZUZ: urea combined with zeolite (15 t ha−1)) on N2O emissions, rice grain yield, and soil physicochemical properties. The results showed that IAWD significantly increased N2O emissions by 18% relative to ICF, and ZUZ significantly reduced N2O emissions under IAWD by 9% compared to ZU. IAWD had no significant effect on rice grain yield compared to ICF. However, ZUZ significantly enhanced rice grain yield under ICF and IAWD by 11% and 14%, respectively, compared to ZU. Accordingly, ZUZ significantly decreased yield-scaled N2O emissions under ICF and IAWD by 13% and 19%, respectively, compared to ZU. Increases in soil NH4+-N concentrations and soil pH contribute to the N2O mitigation in ZUZ under IAWD. Altogether, our results highlight that zeolite combined with urea is likely a sustainable resource-efficient approach for mitigating N2O emissions while increasing rice grain yield in paddy fields under IAWD.

Clinoptilolite zeolite (Z) has been widely used for reducing nutrient loss and improving crop productivity. However, the impacts of zeolite addition on CH4 and N2O emissions in rice fields under various irrigation regimes are still unclear. Therefore, a three-year field experiment using a split-plot design evaluated the effects of zeolite addition and irrigation regimes on greenhouse gas (GHG) emissions, grain yield, water productivity and net ecosystem economic profit (NEEP) in a paddy field. The field experiment included two irrigation regimes (CF: continuous flooding irrigation; AWD: alternate wetting and drying irrigation) as the main plots, and three zeolite additions (0, 5 and 10 t ha−1) as the subplots. The results indicated that AWD regime decreased seasonal cumulative CH4 emissions by 54%–71% while increasing seasonal cumulative N2O emissions by 14%–353% across the three years, compared with CF regime. Consequently, the yield-scaled global warming potential under AWD regime decreased by 10%–60% while grain yield, water productivity and NEEP improving by 4.9%–7.9%, 19%–27% and 12%–14%, respectively, related to CF regime. Furthermore, 5 t ha−1 zeolite addition mitigated seasonal cumulative CH4 emissions by an average of 36%, but did not significantly affect N2O emissions compared with non-zeolite treatment. In addition, zeolite addition at 5 and 10 t ha−1 significantly increased grain yield, water productivity and NEEP by 11%–21%, 13%–20% and 13%–24%, respectively, related to non-zeolite treatment across the three years. Therefore, zeolite addition at 5 t ha−1 coupled with AWD regime could be an eco-economic strategy to mitigate GHG emissions and water use while producing optimal grain yield with high NEEP in rice fields.

This study investigated effects of planting density and harvest interval on SRC willow over six growth years. In a double row system with 0.74 m plant distance and 0.75 m row spacing within double rows, we compared normal (1.5 m) and large (2.62 m) double row spacing, corresponding to 1.2 and 0.8 plants m −2 . Over two three-year harvest rotations with two cultivars, large row spacing reduced mean annual dry matter (DM) yield significantly from 7.0 to 5.3 Mg ha −1 y −1 (23%). Row spacing did not interact with cultivar or harvest rotation. Harvest intervals of one, two or three years were compared for one cultivar on two sites over six years. DM yield generally increased from first to later harvest rotations. Mean annual DM yield increased significantly with increased harvest interval, with 4.9, 6.6 and 8.0 Mg ha −1 y −1 for one-year, two-year and three-year intervals, respectively. This corresponds to a yield reduction of 39 and 17% for annual and biennial harvest, respectively, compared to triennial harvest. The yield for annual harvest may have been affected by weed competition but also browsing. Across shoot ages from one to three years, the concentration of N, P and K in DM decreased non-linearly with a reduction of 53, 58 and 59%, respectively, when DM yield increased from 1.5 to 40.6 Mg ha −1 . Across data from this and 7 published studies, N concentration reached a constant level above 12 Mg ha −1 DM yield. This has implications for optimization of biomass quality and quantification of nutrient removal.

In experimental ecosystem ecology, plot sizes are most often too small to apply eddy flux techniques and estimation of ecosystem gas exchange rates relies on various chamber measurement technologies. Furthermore, drained areas often results in increased growth of trees which complicates application of eddy flux measurements on small plots.We combined ECO2FluX ecosystem-level automatic chambers (prenart.dk) with an LI-8100/LI-8150 multiplexer systems (licor.com) in a range of Danish and Norwegian ecosystems experiments spanning agriculture, grassland/heathlands and peatland ecosystems. The automatic closed, none-steady state chambers each cover an area of 3,117 cm2 (63 cm diameter), are 80 cm tall (volume: 250L), and are capable of switching automatically between transparent and darkened mode, enabling separation of light-sensitive and light-indifferent processes in the ecosystems covered. For CO2 fluxes, net exchange (NEE) was estimated as the flux in transparent mode, ecosystem respiration (RE) in darkened mode, while Gross Ecosystem Productivity (GPP) was estimated as NEE – RE.Chambers were set up to measure gas concentrations every second using enclosure times of 4-5 minutes, first in light mode and 10-30 minutes later in dark mode, with 3-48 repetitions per day. The longest time series spans 5 years of measurements and contain >60,000 point measurements.In this presentation, we will present an analysis of the ability of the light-dark chamber data to infer ecosystem-level rates of gross primary productivity, respiration, net CO2 exchange, and evapotranspiration. In the two Norwegian peatland sites, flux measurements may be compared directly with eddy flux measurements. We also compare the rates of the direct estimates of GPP from the light-dark chamber measurements to estimates inferred from using the light (NEE) measurements only followed by applying methodologies normally used for eddy flux measurements. This comparison may help constrain potential biases in both the closed chamber and eddy flux techniques. Finally, we investigate the ability of using such closed chambers to estimate ecosystem evapotranspiration rates at the plot scale. Such application may be useful for estimating the effects on evapotranspiration in field-scale experiments manipulating the ecosystem water balance either directly or indirectly.

Drainage of peatlands for agriculture causes substantial degradation and finally loss, including associated ecosystem functions, but also creates emission hotspots of carbon dioxide (CO2). Mean CO2 emission from drained temperate grassland on peat was reported by IPCC as 22.4 (18.3-26.7) MgCO2-eq ha-1 y-1 (95% CI) while methane (CH4) emissions were close to zero. Rewetting of peatlands reduces CO2 emissions while at the same time favouring CH4 emissions. From wet or rewetted nutrient-rich grassland, emissions of CO2 and CH4 were reported by IPCC as 1.8 (-2.8-2.8) and9.8 (0-39) Mg CO2-eq ha-1 y-1, respectively (GWP CH4 = 34). The uncertainties of the estimates reflect the large variation among the reported studies, which could be caused by different climate conditions, vegetation, groundwater table (GWT), peat composition and biogeochemistry. A mesocosm experiment was established to assess biogeochemical causes of variation in CO2 and CH4 flux dynamics under controlled GWT for peatsoils derived from five different Danish bogs and fens. A total number of 75 mesocosms were grouped into three treatments: GWT -40 cm, bare; GWT -5 cm, bare; and GWT -5 cm, cultivated with reed canary grass (RCG). GHG fluxes were measured using opaque chambers at biweekly intervals from July 2019 to 2020 and extrapolated to annual values. Preliminary results indicate significant differences regarding CO2 and CH4 fluxes across all sites and depending on soil biogeochemical and physical properties. Rewetting raised the contribution of CH4 most on soils from Store Vildmose and Vejrumbro with 1.9 to 12.9 t CO2eq ha-1 yr-1 and 0.1 to 5.7 t CO2eq ha-1 yr-1, respectively. On an annual average, these high emissions were with 69 % and 48 % mitigated by the cultivation of RCG in a paludiculture scenario. Further, the results show that CH4 spikes of up to 37.5 mg m-2 h-1 at elevated GWT during warmer summer months may be mitigated by cultivation with RCG, with maximum peaks of 2.1 mg m-2 h-1. Soil analyses highlighted distinct differences in the soil mineralogical composition across sites and soil depths.

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

Sustainable agriculture should aim to increase biomass yield and yield stability, while protecting soil carbon (C) and nitrogen (N) content. However, few studies have concurrently explored changes in biomass yield, yield stability and soil C and N content under different cropping systems targeting biorefinery. In this study, 10 different cropping systems were simultaneously investigated from 2012 to 2017 in central Denmark on a loamy sand soil, including (1) two continuous monocultures of annual crops, (2) one optimized crop rotation, (3) five intensively fertilized perennial grasses, and (4) two grass-legume mixtures without nitrogen (N) fertilization. Our results showed that biomass yield and yield stability differed highly across the cropping systems, highlighting crop-specific characteristics. Of the 10 cropping systems, tall fescue significantly increased soil C and N content at 0–20 cm depth, while sustaining high biomass yield and yield stability. There was no clear relationship between biomass yield, yield stability and changes in soil C and N content, challenging some recent findings on the conflicts between increasing biomass yield and protecting soil C and N content. Indeed, the lack of relationships suggest that there is considerable potential to increase biomass yield and yield stability without compromising soil C and N content through selecting proper cropping systems and managements. Altogether, our results underscore how crop-specific documentation of biomass yield, yield stability and changes in soil C and N content on the same experimental platform can advance the understanding of sustainable agriculture for biorefineries, although long-term continuous observations are still required to better clarify the relations between them.

How much can we increase biomass yield by promoting land conversion from annual to perennial crops? Will increased biomass extraction for biorefineries reduce soil organic carbon (SOC) and total nitrogen (TN) stock? Which cropping system is more stable for biomass production over time? To our knowledge, no study has concurrently investigated the effects of land conversion from annual to perennial crops on biomass yield, yield stability, and changes in SOC and TN stock, which limits the understanding and application of sustainable agroecosystems producing biomass for biorefineries. Based on five-year continuous observations in central Jutland Denmark, our results showed that perennial crops significantly increased biomass yield by 19% and yield stability by 88% compared to annual crops. Perennial crops significantly increased SOC content by 4% and SOC stock by 11% at 0–100 cm depth across the five years. The opposite responses of SOC content and stock under annual and perennial crops led to even more significant differences between the crop types. Perennial crops had no effect on soil TN content and increased soil TN stock to one meter depth by 22%, whereas continuous annual crops had no effect on it. Neither annual nor perennial crops had effects on SOC and TN stock when estimated based on equivalent soil mass because the soil density increased under perennial crops. Our results showed that changes in SOC and TN stock between annual and perennial crops varied with the specific calculating methods (fixed depth/equivalent mass), thus the selected methods should be clearly defined in the future research. Increases in SOC content at one meter depth were positively correlated with biomass yield and yield stability, suggesting a win-win strategy for climate mitigation and food security. Altogether, our results highlight the potential to redesign the current cropping system for sustainable intensification by selecting proper perennial crops for green biorefineries.

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 (CO

Drained riparian wetlands have been rewetted and restored in recent decades to remove nutrients, increase biodiversity, and mitigate soil carbon dioxide (CO2) emissions. Yet, few studies have documented the long-term effects of rewetting on complete greenhouse gas (GHG) balances including emissions of CO2, methane (CH4), and nitrous oxide (N2O). Here, we report the complete annual GHG balance of an extensively managed riparian wetland, dominated by creeping bentgrass (Agrostis stolonifera), 12 years after rewetting. Net ecosystem exchange (NEE) of CO2 was measured by transparent closed chambers, and fluxes were partitioned into gross primary production (GPP) and ecosystem respiration (ER) for modelling and extrapolation to annual emissions based on photosynthetically active radiation, ratio vegetation index and temperature. Fluxes of CH4 and N2O were monitored with opaque chambers. Groundwater table (GWT) was close to soil surface for most of the growing period, whereas the site was inundated during winter. Biomass was cut in late summer (8.5 Mg dry weight ha−1), but left on-site according to current management in the area. Annual ER (1360 g CO2-C m−2) exceeded GPP (–1140 g CO2-C m−2), and the ecosystem was a net source of CO2 with NEE of 220 g CO2-C m−2 yr−1. However, fluxes of CH4 (53 g CH4 m−2 yr−1) dominated the annual GHG balance with 405 g CO2-Ceq m−2 yr−1 which contributed 60% to the total GHG balance. Fluxes of N2O were primarily found at times of changing GWT with annual emission of 0.7 g N2O m−2 (50 g CO2-Ceq m−2) equal to 7% of the complete GHG balance. With proper management, rewetting and restoration of wetlands is expected to eventually resume the carbon sink function of natural wetlands, but this was not found in the present study as net fluxes of both CO2 and CH4 were positive. This was mainly attributed to on-site deposition of biomass which apparently stimulated both CO2 and CH4 emissions and partly reduced GPP by acting as a mulch layer. Future studies should focus on managements that increase CO2 uptake and biomass yield, and at the same time reduce CH4 emissions; such managements should avoid on-site deposition of aboveground biomass at rewetted sites. Drained riparian wetlands have been rewetted and restored in recent decades to remove nutrients, increasebiodiversity, and mitigate soil carbon dioxide (CO2) emissions. Yet, few studies have documented the long-termeffects of rewetting on complete greenhouse gas (GHG) balances including emissions of CO2, methane (CH4), andnitrous oxide (N2O). Here, we report the complete annual GHG balance of an extensively managed riparianwetland, dominated by creeping bentgrass (Agrostis stolonifera), 12 years after rewetting. Net ecosystem exchange(NEE) of CO2 was measured by transparent closed chambers, and fluxes were partitioned into grossprimary production (GPP) and ecosystem respiration (ER) for modelling and extrapolation to annual emissionsbased on photosynthetically active radiation, ratio vegetation index and temperature. Fluxes of CH4 and N2Owere monitored with opaque chambers. Groundwater table (GWT) was close to soil surface for most of thegrowing period, whereas the site was inundated during winter. Biomass was cut in late summer (8.5 Mg dryweight ha−1), but left on-site according to current management in the area. Annual ER (1360 g CO2-Cm−2)exceeded GPP (–1140 g CO2-Cm−2), and the ecosystem was a net source of CO2 with NEE of 220 g CO2-Cm−2 yr−1. However, fluxes of CH4 (53 g CH4m−2 yr−1) dominated the annual GHG balance with 405 g CO2-Ceqm−2 yr−1 which contributed 60% to the total GHG balance. Fluxes of N2O were primarily found at times ofchanging GWT with annual emission of 0.7 g N2Om−2 (50 g CO2-Ceqm−2) equal to 7% of the complete GHGbalance. With proper management, rewetting and restoration of wetlands is expected to eventually resume thecarbon sink function of natural wetlands, but this was not found in the present study as net fluxes of both CO2and CH4 were positive. This was mainly attributed to on-site deposition of biomass which apparently stimulatedboth CO2 and CH4 emissions and partly reduced GPP by acting as a mulch layer. Future studies should focus onmanagements that increase CO2 uptake and biomass yield, and at the same time reduce CH4 emissions; suchmanagements should avoid on-site deposition of aboveground biomass at rewetted sites.

Paludiculture, defined as agriculture on wet or rewetted peatlands has been proposed as a mitigation strategy to reverse unsustainable environmental impacts such as land subsidence, nutrient release to surface water and greenhouse gas emissions from traditional agriculture on drained peatland. In particular, the production of biomass feedstock from flood-tolerant perennial grasses for green biorefining to protein and other value-added products may be a viable economic and environmentally sustainable option for temperate peatlands. However, optimal quality characteristics of the biomass for protein extraction have yet to be defined.In 2018, field plots cultivated with different flood-tolerant perennial grasses were established in an agricultural fen peatland in Denmark. Of these, a total of eight plots cultivated with reed canary grass (RCG) and tall fescue were each subdivided into six sub-plots with different management regarding harvest and fertilisation. Harvest frequencies ranged from one to five times in the period between mid-May to mid-October at intervals of 4-6 weeks. The sub-plots received fertilisation of 100 kg ha-1 of both N and K prior to each harvest. Protein extractability of the grasses was assessed by lab-scale biorefinery techniques using a screw press followed by precipitation of true protein in the resulting juice. This was compared with protein fractions classified by the Cornell Net Carbohydrate and Protein System (CNCPS). The biorefinery extractable protein yields (fresh weight) ranged from 10 % to 25 % of the fresh mass input, dependent on treatment, with summer harvests having the lowest yield. Evaluation of the easily extractable crude protein (CP) CNCPS fractions B1 and B2 showed yields of between 61.8 – 110.7 g CP kg-1 DM. Preliminary processing of data showed that the cumulative yields of extractable crude protein for the growing season seem highly affected by management.

Yield and nutrient uptake of willow cultivars are important factors for long-term feasibility and sustainability of willow short rotation coppice (SRC). This study investigated biomass yield of eight willow cultivars (Inger, Klara, Linnea, Resolution, Stina, Terra Nova, Tora, Tordis) during two three-year harvest rotations on four Danish sites. Also, concentration and uptake of N, P and K was measured in harvested biomass in 2nd harvest rotation on two of the sites. Dry matter (DM) yield differed significantly between sites in both 1st and 2nd harvest rotation, but the relative difference between sites decreased from 106 to 54 %. Mean DM yield across cultivars and sites increased 67 % from 1st to 2nd harvest rotation but ranging from 44 to 108 % between sites. There were certain significant differences in yield ranking of cultivars between sites and harvest rotations but, overall, ranking was rather consistent. Across all four sites and all six growth years, there were four cultivar groups differing significantly in DM yield, with highest yield in Tordis and Tora, second highest in Klara and Resolution followed by Terra Nova and Inger and lowest yield in Linnea and Stina, with Stina having 39 % lower yield than Tordis. Concentration and uptake of N, P and K in harvested biomass in 2nd harvest rotation differed significantly between cultivars and between sites. Across cultivars and sites, nutrient concentration decreased linearly with increasing DM yield, whereas nutrient uptake increased linearly. These results have implications for nutrient balance and fertilization strategies for willow SRC.

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.

Perennial grass-based systems targeting biomass supply to future biorefineries are characterized by overall higher resource use efficiency and improved environment, compared to annual cereal-based systems. The biomass yield potentials also depend on plant physiology, i.e., how many harvests can the crop withstand and how much biomass and protein are obtained. The current study aims to understand the complex interaction between species, harvest height and frequency, and nitrogen (N) application rate. Field experiments started in 2019 in Denmark to test the effect of harvest frequency (two, four and six weeks) and height (7-9 and 12-14 cm), as well as N fertilizer input (zero, 300 and 500 kg N ha-1 yr-1) on biomass and protein yield of grasses (perennial ryegrass and tall fescue), legumes (alfalfa and red clover) and their mixture. The results of the establishment year point on red clover and the highly fertilized grasses harvested at 7-9 cm height and medium frequency to produce more biomass compared to the other treatments. Complementary results from previous study at the same site show high biomass and protein yields and low N losses from highly fertilized grasses and unfertilized grass-legume mixtures harvested three- to four times annually.

In Northern, Eastern and Central European countries, peat soils drained for agriculture are a considerable source of greenhouse gas emissions. Since emissions from this source have high mitigation potential, they will likely be a focus of the European Union’s future climate goals. We describe and compare the similarities and differences in the socioeconomic and ecological business environment that policy makers, planners and farmers are confronted with when developing tailored proposals for low emission land use alternatives on peat land. The analysis is based on interviews with 33 typical farmers cultivating organic soils and on expert group discussions held in six different Northern, Eastern and Central European regions. Based on the Social-Ecological System Framework we identify and cluster important variables. Our results show that mainly hard economic variables determine preferred land use alternatives: the productivity of resource systems, the economic value of land and market incentives. Other variables, such as the heterogeneity of users and conflicts among them, are more important with respect to the implementation of alternatives. We point out possibilities to transfer solutions between regions and discuss an institutional framework for European Union, national and regional levels for facilitating implementation potential.

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.

In this study, we report efficiencies of light capture and biomass yield of festulolium and tall fescue cultivated on a riparian fen in Denmark under different harvesting managements. Green biomass targeted for biogas production was harvested either as two cuts (2C) or three cuts (3C) in a year. Three different timings of the first cut in the 2C systems were included as early (2C-early), middle (2C-mid) and late (2C-late) cuts corresponding to pre-heading, inflorescence emergence and flowering stages, respectively. The fraction of intercepted photosynthetically active radiation (f PAR ) was derived from the canopy reflectance measured on 61 dates throughout a year, and cumulative interception of PAR (IPAR) and radiation use efficiency (RUE) was calculated. The dynamics of f PAR and biomass accumulations was similar for both crops before the first cuts in all managements. Festulolium f PAR in 2C-early and 2C-mid managements declined faster than in 2C-late and 3C managements in the second growth period and thus growing period IPAR of 2C-early and 2C-mid declined by 8% as compared to 3C management where IPAR was 925 MJ m −2 . Annual festulolium dry matter (DM) yield in 2C-early and 2C-mid managements (average 14.1 Mg DM ha −1 ) decreased by 22% compared to 3C management (18.2 Mg DM ha −1 ). The highest and the lowest RUE of festulolium were observed in 3C and 2C-mid managements as 1.97 and 1.59 g MJ −1 , respectively. For tall fescue f PAR declined rather slowly in the second growing period in all 2C managements, which contributed to similar IPAR (908–919 MJ m −2 ), total biomass yield (16.4–18.8 Mg DM ha −1 yr −1 ) and RUE (1.80–2.07 g MJ −1 ) for all managements. Whereas both crops were highly productive under both 3C management and 2C management with first harvest after flowering (i.e., 2C-late), the 2C-late strategy is recommended as the least intensive of the two management systems.

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.

Drought is a great challenge to agricultural production, and cultivation of drought-tolerant or water use-efficient cultivars is important to ensure high biomass yields for bio-refining and bioenergy. Here, we evaluated drought tolerance of four C3 species, Dactylis glomerata cvs. Sevenop and Amba, Festuca arundinacea cvs. Jordane and Kora, Phalaris arundinacea cvs. Bamse and Chieftain and Festulolium pabulare cv. Hykor, and two C4 species Miscanthus × giganteus and M. lutarioriparius. Control (irrigated) and drought-treated plants were grown on coarse and loamy sand in 1 m2 lysimeter plots where rain was excluded. Drought periods started after harvest and lasted until 80% of available soil water had been used. Drought caused a decrease in dry matter yield (DM; P < 0.001) for all species and cultivars during the drought period. Cultivars Sevenop, Kora and Jordane produced DM at equal levels and higher than the other C3 cultivars in control and drought-treated plots both during and after the drought period. Negative correlations were observed between stomatal conductance (gs) and leaf water potential (P < 0.01) and positive correlations between gs and DM (P < 0.05) indicating that gs might be suitable for assessment of drought stress. There were indications of positive associations between plants carbon isotope composition and water use efficiency (WUE) as well as DM under well-watered conditions. Compared to control, drought-treated plots showed increased growth in the period after drought stress. Thus, the drought events did not affect total biomass production (DMtotal) of the whole growing season. During drought stress and the whole growing season, WUE was higher in drought-treated compared to control plots, so it seems possible to save water without loss of biomass. Across soil types, M. lutarioriparius had the highest DMtotal (15.0 t ha−1), WUEtotal (3.6 g L−1) and radiation use efficiency (2.3 g MJ−1) of the evaluated grasses. Drought is a great challenge to agricultural production, and cultivation of drought-tolerant or water use-efficient cultivars is important to ensure high biomass yields for bio-refining and bioenergy. Here, we evaluated drought tolerance of four C3 species, Dactylis glomerata cvs. Sevenop and Amba, Festuca arundinacea cvs. Jordane and Kora, Phalaris arundinacea cvs. Bamse and Chieftain and Festulolium pabulare cv. Hykor, and two C4 species Miscanthus × giganteus and M. lutarioriparius. Control (irrigated) and drought-treated plants were grown on coarse and loamy sand in 1 m2 lysimeter plots where rain was excluded. Drought periods started after harvest and lasted until 80% of available soil water had been used. Drought caused a decrease in dry matter yield (DM; P < 0.001) for all species and cultivars during the drought period. Cultivars Sevenop, Kora and Jordane produced DM at equal levels and higher than the other C3 cultivars in control and drought-treated plots both during and after the drought period. Negative correlations were observed between stomatal conductance (gs) and leaf water potential (P < 0.01) and positive correlations between gs and DM (P < 0.05) indicating that gs might be suitable for assessment of drought stress. There were indications of positive associations between plants carbon isotope composition and water use efficiency (WUE) as well as DM under well-watered conditions. Compared to control, drought-treated plots showed increased growth in the period after drought stress. Thus, the drought events did not affect total biomass production (DMtotal) of the whole growing season. During drought stress and the whole growing season, WUE was higher in drought-treated compared to control plots, so it seems possible to save water without loss of biomass. Across soil types, M. lutarioriparius had the highest DMtotal (15.0 t ha−1), WUEtotal (3.6 g L−1) and radiation use efficiency (2.3 g MJ−1) of the evaluated grasses.

Peatlands drained for agriculture are sources of atmospheric carbon dioxide (CO2) and nitrous oxide (N2O). Resulting emissions may depend on land-use, often as grassland or cropland, but few studies have directly compared the effects of land-uses. Here, we measured annual emissions of CO2, N2O and methane (CH4) from five sites in a temperate bog, representing an undrained natural bog (NB) site, and four drained sites used as permanent grassland (PG) and croplands with rotations of oat-potato, oat-spring barley and potato-spring barley (PO:SB) in the study year. Gas fluxes were measured at 1–2 week intervals using static chambers, and auxiliary data were obtained, such as temperature, depth of water table, ratio-vegetation index, pH and soil mineral N. Annual CO2 emissions were derived from empirical modelling, whereas CH4 and N2O emissions were linearly interpolated between measurement dates by bootstrapping. Soil respiration was lower at the NB site (1.8 Mg CO2-C ha−1 yr−1) than at the drained sites where emissions were in the range of 5.0–8.8 Mg CO2-C ha−1 yr−1. The N2O emission was negligible at NB (0.3 kg N2O ha−1 yr−1), low at three of the drained sites (1.5–3.7 kg N2O ha−1 yr–1), but high at PO:SB (37.7 kg N2O ha−1 yr−1). The CH4 emission was high at NB (172 kg CH4 ha−1 yr−1), but negligible at the drained sites (−1.5 to 1.5 kg CH4 ha−1 yr−1). The soil respiration at the drained sites indicated that peat losses were rather similar among the different cropping systems and depended mostly on drainage status, although soil respiration and peat mineralization may not scale directly. The pattern of N2O emissions suggested an increased risk of N2O emission from potato cultivation before and after the period of potato growth, likely due to microbial availability of NO3– outside the growing season. For initiatives aiming at reduction of greenhouse gas emissions from agricultural peat soils, this means that, e.g., conversion from cropland to permanent grassland should preferably be accompanied by measures of rewetting, whereas for potato cropping, N availability outside the growing season should be minimized.

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.

Future biorefineries will prefer crops with high biomass yields, thus may precipitate fundamental changes to the agricultural landscape and the biomass production systems. Understanding the fate of nitrogen (N) in novel agricultural land uses is vital for product optimisation and environmental protection. This work reports and investigates the first multi-annual N balances for novel cropping systems optimised for high biomass production compared to traditional systems under North European climate and soil conditions. In a three-year study, two types of novel systems, i) a rotation of annual crops optimised for maximum biomass production (maize, beet, hemp/oat, triticale as main crops, and winter rye and winter oilseed rape as “second” - cover crops), and ii) perennial grasses (intensively fertilised (festulolium, reed canary grass, tall fescue and cocksfoot), low-fertilised (miscanthus) and unfertilised (grass-legume mixtures)), were compared with iii) traditional systems (continuous maize or triticale, and a cereal crop rotation) at two sites in Denmark varying in temperature, rainfall and soil type (sandy loam and coarse sand). Harvested biomass N and soil nitrate dynamics, as well as model-supported nitrate leaching and field surface N balance (input minus output) of the systems were compared. At each study site, the fertilised perennial grasses outperformed all other systems by doubling biomass N and reducing nitrate leaching by 70–80% compared to the traditional systems. Compared to continuous maize monoculture, the optimised rotation supplied 70% more biomass N and 40% less nitrate leaching on coarse sandy soil, whereas on sandy loam soil it yielded about 10% less biomass N with 50% less nitrate leaching. Field surface N balances were overall neutral/positive, except for festulolium and continuous maize monoculture that slightly mined the soil for N. When N losses by leaching, denitrification and volatilisation were included, soil total N stocks were estimated to decline for the majority of the systems at both sites.

Establishing an environment-friendly industrial biorefinery production requires resource efficient agroecosystems with low losses to the environment, especially of nitrogen (N). This work reports the first field-based N losses and balances for agro-ecosystems optimised for biomass production for biorefinery under northEuropean climate and soil settings

A growing bioeconomy demands high, but sustainable production of biomass. In contrast to annual crops, perennial crops may combine high biomass yields with low nitrogen (N) leaching losses despite intensive management. However, there is an important trade-off between N fertilization to increase biomass production and the associated nitrous oxide (N2O) emissions when estimated with the IPCC default emission factor (EF) of 1% of applied N. Actual N2O emissions may vary with crop species and site conditions, and a field experiment was therefore conducted to determine N2O emissions and biomass yields from selected perennial crops. Three perennial crops were established five years prior to this study, including festulolium (x Festulolium braunii) and tall fescue (Festuca arundinacea), both receiving 425 kg N ha−1 in NPK fertilizer with 60% ammonium-N and 40% nitrate-N, and grass-clover (Lolium perenne-Trifolium pretense) receiving PK fertilizer only. Maize (Zea mays) receiving 140 kg N ha−1 in NPK was included as a reference annual crop; all treatments had unfertilized subplots. The total biomass yields of fertilized maize (14.3 Mg DM ha−1), festulolium (15.3 Mg DM ha−1) and tall fescue (16.2 Mg DM ha−1) were similar, and higher than grass-clover yield (8.4 Mg DM ha−1). There were three cuts in perennial crops, and peak emissions of N2O occurred after cutting and fertilization. Unexpectedly, PK fertilization increased N2O emissions by 89% compared to unfertilized grass-clover. A mixed-effect model examining drivers of N2O emissions after each fertilization indicated that temperature and nitrate were more important for N2O emissions than soil wetness, whether this was expressed as water-filled pore space or relative gas diffusivity, Dp/D0. The overall highest emissions of N2O, which occurred in festulolium and tall fescue after the 1st cut and 2nd fertilization, coincided with rainfall after a dry period. Measurements of soil respiration indicated that these high N2O emissions were triggered by a release of labile carbon after the rapid wetting, and hence that denitrification of nitrate in the fertilizer applied was a significant source. Fertilization increased N2O emissions two- to three-fold compared to treatments without fertilization, but the annual emission factors for fertilizer N were consistently below the default IPCC emission factor of 1% with 0.23 ± 0.04, 0.32 ± 0.03 and 0.54 ± 0.13% for, respectively, festulolium, tall fescue and maize. Hence, this study suggests that intensively managed perennial crops can be used for biomass production on sandy loam soil without excessive N2O emissions compared to annual crops.

Miscanthus × giganteus is a perennial grass that is considered to have a high feedstock potential for bioenergy production. Assessment of that potential is however highly related to the crop yields and to their change through the crop lifetime, which is expected to be longer than 20 years. M. giganteus is known to have an establishment phase during which annual yields increased as a function of crop age, followed by a ceiling phase, the duration of which is unknown. We built a database including 16 European long-term experiments (i) to describe the yield evolution during the establishment and the ceiling phases and (ii) to determine whether M. giganteus ceiling phase is followed by a decline phase where yields decrease across years. Data were analyzed through comparisons between a set of statistical growth models. The model that best fitted the experimental data included a decline phase. The decline intensity and the value of several other model parameters, such as the maximum yield reached during the ceiling phase or the duration of the establishment phase, were highly variable. The highest maximum yields were obtained in the experiments located in the southern part of the studied area and the duration of the establishment phase was strongly related to the establishment method. Since energetic viability and profitability of M. giganteus hinge critically on yields, these results could be integrated in further assessment works. Miscanthus × giganteus is a perennial grass that is considered to have a high feedstock potential for bioenergy production. Assessment of that potential is however highly related to the crop yields and to their change through the crop lifetime, which is expected to be longer than 20 years. M. giganteus is known to have an establishment phase during which annual yields increased as a function of crop age, followed by a ceiling phase, the duration of which is unknown. We built a database including 16 European long-term experiments (i) to describe the yield evolution during the establishment and the ceiling phases and (ii) to determine whether M. giganteus ceiling phase is followed by a decline phase where yields decrease across years. Data were analyzed through comparisons between a set of statistical growth models. The model that best fitted the experimental data included a decline phase. The decline intensity and the value of several other model parameters, such as the maximum yield reached during the ceiling phase or the duration of the establishment phase, were highly variable. The highest maximum yields were obtained in the experiments located in the southern part of the studied area and the duration of the establishment phase was strongly related to the establishment method. Since energetic viability and profitability of M. giganteus hinge critically on yields, these results could be integrated in further assessment works.

Climate change impacts rainfall patterns which may lead to drought stress in rain-fed agricultural systems. Crops with higher drought tolerance are required on marginal land with low precipitation or on soils with low water retention used for biomass production. It is essential to obtain plant breeding tools, which can identify genotypes with improved drought tolerance and water use efficiency (WUE). In C3 plant species, the variation in discrimination against 13C (Δ13C) during photosynthesis has been shown to be a potential indicator for WUE, where discrimination against 13C and WUE were negatively correlated. The aim of this study was to determine the variation in the discrimination against 13C between species and cultivars of three perennial C3 grasses (Dactylis glomerata (cocksfoot), Festuca arundinacea (tall fescue) and Phalaris arundinacea (reed canary grass)) and test the relationships between discrimination against 13C, season-long water use WUEB, shoot and root biomass production in plants grown under well-watered and water-limited conditions. The grasses were grown in the greenhouse and exposed to two irrigation regimes, which corresponded to 25% and 60% water holding capacity, respectively. We found negative relationships between discrimination against 13C and WUEB and between discrimination against 13C and shoot biomass production, under both the well-watered and water-limited growth conditions (p < 0.001). Discrimination against 13C decreased in response to water limitation (p < 0.001). We found interspecific differences in the discrimination against 13C, WUEB, and shoot biomass production, where the cocksfoot cultivars showed lowest and the reed canary grass cultivars highest values of discrimination against 13C. Cocksfoot cultivars also showed highest WUEB, shoot biomass production and potential tolerance to water limitation. We conclude that discrimination against 13C appears to be a useful indicator, when selecting C3 grass crops for biomass production under drought conditions.

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 (