• Authors:
    • De Nocker, L.
    • Aertsens, J.
    • Gobin, A.
  • Source: Land Use Policy
  • Volume: 31
  • Year: 2013
  • Summary: Purpose: This paper aims at indicating the potential of agricultural measures in sequestering carbon as an option for climate change mitigation. The related value for society is estimated. Principle results: Agricultural practices like agroforestry, introducing hedges, low and no tillage and cover crops have an important potential to increase carbon sequestration. The total technical potential in the EU-27 is estimated to be 1566 million tonnes CO2-equivalent per year. This corresponds to 37% of all CO2-equivalent emissions in the EU in 2007. The introduction of agroforestry is the measure with the highest potential, i.e. 90% of the total potential of the measures studied. Taking account only of the value for climate change mitigation, the introduction of agroforestry is estimated to have a value of 282 euro/ha in 2012 that will gradually increase to 1007 euro/ha in 2030. Major conclusions: This implies that there is a huge potential which represents an important value for society in general and for the agricultural sector in specific. At the European level, only in the last few years policy makers have recognized the important benefits of agroforestry. In their rural development programmes some European countries now support farmers to introduce agroforestry. But still the current level of support is only a small fraction of the societal value of agroforestry. If this value would be fully recognized by internalizing the positive externality, we expect that agroforestry will be introduced to a very large extent in the next decades, in Europe and the rest of the world, and this will importantly change the rural landscapes. (C) 2012 Elsevier Ltd. All rights reserved.
  • Authors:
    • Borgesen, C. D.
    • Kristensen, I. T.
    • Hermansen, J. E.
    • Olesen, J. E.
    • Elsgaard, L.
  • Source: Acta Agriculturae Scandinavica, Section B — Soil & Plant Science
  • Volume: 63
  • Issue: 3
  • Year: 2013
  • Summary: Biofuels from bioenergy crops may substitute a significant part of fossil fuels in the transport sector where, e.g., the European Union has set a target of using 10% renewable energy by 2020. Savings of greenhouse gas emissions by biofuels vary according to cropping systems and are influenced by such regional factors as soil conditions, climate and input of agrochemicals. Here we analysed at a regional scale the greenhouse gas (GHG) emissions associated with cultivation of winter wheat for bioethanol and winter rapeseed for rapeseed methyl ester (RME) under Danish conditions. Emitted CO2 equivalents (CO2eq) were quantified from the footprints of CO2, CH4 and N2O associated with cultivation and the emissions were allocated between biofuel energy and co-products. Greenhouse gas emission at the national level (Denmark) was estimated to 22.1 g CO2eq MJ(1) ethanol for winter wheat and 26.0 g CO2eq MJ(1) RME for winter rapeseed. Results at the regional level (level 2 according to the Nomenclature of Territorial Units for Statistics [NUTS]) ranged from 20.0 to 23.9 g CO2eq MJ(1) ethanol and from 23.5 to 27.6 g CO2eq MJ(1) RME. Thus, at the regional level emission results varied by up to 20%. Differences in area-based emissions were only 4% reflecting the importance of regional variation in yields for the emission result. Fertilizer nitrogen production and direct emissions of soil N2O were major contributors to the final emission result and sensitivity analyses showed that the emission result depended to a large extent on the uncertainty ranges assumed for soil N2O emissions. Improvement of greenhouse gas balances could be pursued, e.g., by growing dedicated varieties for energy purposes. However, in a wider perspective, land-use change of native ecosystems to bioenergy cropping systems could compromise the CO2 savings of bioenergy production and challenge the targets set for biofuel production.
  • Authors:
    • Hauggard-Nielsen, H.
    • Jensen, E. S.
    • Carter, M. S.
    • Johansen, A.
    • Ambus, P.
  • Source: Applied Soil Ecology
  • Volume: 63
  • Issue: January
  • Year: 2013
  • Summary: Anaerobic digestion of animal manure and crop residues may be employed to produce biogas as a climate-neutral source of energy and to recycle plant nutrients as fertilizers. However, especially organic farmers are concerned that fertilizing with the digestates may impact the soil microbiota and fertility because they contain more mineral nitrogen (N) and less organic carbon (C) than the non-digested input materials (e.g. raw animal slurry or fresh plant residues). Hence, an incubation study was performed where (1) water, (2) raw cattle slurry, (3) anaerobically digested cattle slurry/maize, (4) anaerobically digested cattle slurry/grass-clover, or (5) fresh grass-clover was applied to soil at arable realistic rates. Experimental unites were sequentially sampled destructively after 1, 3 and 9 days of incubation and the soil assayed for content of mineral N, available organic C, emission of CO2 and N2O, microbial phospholipid fatty acids (biomass and community composition) and catabolic response profiling (fiinctional diversity). Fertilizing with the anaerobically digested materials increased the soil concentration of NO3- ca. 30-40% compared to when raw cattle slurry was applied. Grass-clover contributed with four times more readily degradable organic C than the other materials, causing an increased microbial biomass which depleted the soil for mineral N and probably also O-2. Consequently, grass-clover also caused a 10 times increase in emissions of CO2 and N2O greenhouse gasses compared to any of the other treatments during the 9 days. Regarding microbial community composition, grass-clover induced the largest changes in microbial diversity measures compared to the controls, where raw cattle slurry and the two anaerobically digested materials (cattle slurry/maize, cattle slurry/grass-clover) only induced minor and transient changes. (C) 2012 Elsevier B.V. All rights reserved.
  • Authors:
    • Laerke, P. E.
    • Elsgaard, L.
    • Kandel, T. P.
  • Source: GCB Bioenergy
  • Volume: 5
  • Issue: 5
  • Year: 2013
  • Summary: Cultivation of bioenergy crops has been suggested as a promising option for reduction of greenhouse gas (GHG) emissions from arable organic soils (Histosols). Here, we report the annual net ecosystem exchange (NEE) fluxes of CO2 as measured with a dynamic closed chamber method at a drained fen peatland grown with reed canary grass (RCG) and spring barley (SB) in a plot experiment (n=3 for each cropping system). The CO2 flux was partitioned into gross photosynthesis (GP) and ecosystem respiration (R-E). For the data analysis, simple yet useful GP and R-E models were developed which introduce plot-scale ratio vegetation index as an active vegetation proxy. The GP model captures the effect of temperature and vegetation status, and the R-E model estimates the proportion of foliar biomass dependent respiration (R-fb) in the total R-E. Annual R-E was 1887 +/- 7 (mean +/- standard error, n=3) and 1288 +/- 19g CO2-Cm-2 in RCG and SB plots, respectively, with R-fb accounting for 32 and 22% respectively. Total estimated annual GP was -1818 +/- 42 and -1329 +/- 66g CO2-Cm-2 in RCG and SB plots leading to a NEE of 69 +/- 36g CO2-C m(-2)yr(-1) in RCG plots (i.e., a weak net source) and -41 +/- 47g CO2-C m(-2)yr(-1) in SB plots (i.e., a weak net sink). Standard errors related to spatial variation were small (as shown above), but more significant uncertainties were related to the modelling approach for establishment of annual budgets. In conclusion, the bioenergy cropping system was not more favourable than the food cropping system when looking at the atmospheric CO2 emissions during cultivation. However, in a broader GHG life-cycle perspective, the lower fertilizer N input and the higher biomass yield in bioenergy cropping systems could be beneficial.
  • Authors:
    • Prochnow, A.
    • Olesen, J. E.
    • Meyer-Aurich, A.
    • Brunsch, Reiner
  • Source: Mitigation and Adaptation Strategies for Global Change
  • Volume: 18
  • Issue: 7
  • Year: 2013
  • Summary: Agricultural lands have been identified to mitigate greenhouse gas (GHG) emissions primarily by production of energy crops and substituting fossil energy resources and through carbon sequestration in soils. Increased fertilizer input resulting in increased yields may reduce the area needed for crop production. The surplus area could be used for energy production without affecting the land use necessary for food and feed production. We built a model to investigate the effect of changing nitrogen (N) fertilizer rates on cropping area required for a given amount of crops. We found that an increase in nitrogen fertilizer supply is only justified if GHG mitigation with additional land is higher than 9-15 t carbon dioxide equivalents per hectare (CO2-eq.(.)/ha). The mitigation potential of bioenergy production from energy crops is most often not in this range. Hence, from a GHG abatement point of view land should rather be used to produce crops at moderate fertilizer rate than to produce energy crops. This may change if farmers are forced to reduce their N input due to taxes or governmental regulations as it is the case in Denmark. However, with a fertilizer rate 10 % below the economical optimum a reduction of N input is still more effective than the production of bioenergy unless mitigation effect of the bioenergy production exceeds 7 t carbon dioxide (CO2)-eq.(.)/ha. An intensification of land use in terms of N supply to provide more land for bioenergy production can only in exceptional cases be justified to mitigate GHG emissions with bioenergy under current frame conditions in Germany and Denmark.
  • Authors:
    • Petersen,Soren O.
    • Schjonning,Per
    • Olesen,Jorgen E.
    • Christensen,Soren
    • Christensen,Bent T.
  • Source: Soil Science Society of America Journal
  • Volume: 77
  • Issue: 1
  • Year: 2013
  • Summary: In organic cropping systems, legumes, cover crops (CC), residue incorporation, and manure application are used to maintain soil fertility, but the contributions of these management practices to soil nitrogen (N) supply remain obscure. We examined potential sources of N for winter wheat (Triticum aestivum L.) in four experimental cropping systems established in 1997 on three soil types. Three of the four systems were under organic management. Topsoil N, depth of the A horizon, and cumulated inputs of N since 1997 were determined at plot level. Labile soil N pools [mineral N, potentially mineralizable N (PMN), microbial biomass N (MBN)] were monitored during two growth periods; at one site, biomass C/N ratios were also determined. Soil for labile N analysis was shielded from N inputs during spring application to isolate cumulated system effects. Potentially mineralizable N and MBN were correlated across all sites and rotations (r(2) = 0.72). The MBN corresponded to 46 to 85, 85 to 145, and 74 to 172 kg N ha(-1) at the three sites and differed significantly between cropping systems, but MBN could not explain differences in wheat grain N yields. Instead, a multiple linear regression model explained 76 and 82% of the variation in grain N yields in organic cropping systems in 2007 and 2008, showing significant effects of, respectively, topsoil N, depth of A horizon, cumulated inputs of N, and N applied to winter wheat in manure. Thus, soil properties and past and current management all contributed to winter wheat N supply.
  • Authors:
    • Lindedam, J.
    • Bruun, S.
    • Larsen, S.
  • Source: Biomass & Bioenergy
  • Volume: 45
  • Year: 2012
  • Summary: Straw is a by-product from cereal production which constitutes a considerable biomass resource, for instance for 2G ethanol production. Straw yield per hectare and straw quality in terms of ethanol production are both important factors for the available biomass resource and the potential ethanol production per hectare. In a series of field trials on three locations in 2009, we compared straw and grain yield from the winter cereal species triticale, winter barley, winter rye, and winter wheat. Grain yield did not differ significantly between the species, but winter rye yielded up to 59% more straw dry matter than the other species. The release of glucose and xylose after pretreatment and enzymatic hydrolysis i.e. the saccharification potential was used to indicate the potential for ethanol production. The saccharification potential did not differ between species, but due to the differences in straw yield, areal saccharification potential (i.e. potential sugar production per hectare) was from 29% to 78% higher for winter rye than for other species. In a series of winter wheat cultivar trials on two locations in 2008 and three locations in 2009, straw yield differed significantly between cultivars in both years and across years. The highest yielding cultivar yielded up to 57% and 37% more straw than the lowest yielding cultivar in the two years, respectively, even among cultivars with non-significant differences in grain yield. The saccharification potential was measured from straw of winter wheat cultivar trials harvested in 2009. The potential varied largely but was not significantly affected by neither cultivar nor location. Due to cultivar differences in straw yield, however, areal saccharification potential differed significantly between cultivars with up to 38% difference in glucose yield and up to 35% in xylose yield. Straw yield increased with increasing grain yield, but the straw:grain ratio differed significantly between cultivars and was not consistent across years and locations. This has implications for straw resource estimates when these are based on the relationship between grain yield and straw yield. In conclusion, it appears possible to choose species and cultivars with higher straw yield and consequently larger potential for ethanol production per hectare without compromising grain yield. This may provide a means of increasing the overall straw resource, as long as increased straw yield is not accompanied by negative effects such as increased tendency to lodging.
  • Authors:
    • Astrup, T.
    • Wenzel, H.
    • Hamelin, L.
    • Tonini, D.
  • Source: Environmental Science & Technology
  • Volume: 46
  • Issue: 24
  • Year: 2012
  • Summary: In the endeavor of optimizing the sustainability of bioenergy production in Denmark, this consequential life cycle assessment (LCA) evaluated the environmental impacts associated with the production of heat and electricity from one hectare of Danish arable land cultivated with three perennial crops: ryegrass (Lolium perenne), willow (Salix viminalis) and Miscanthus giganteus. For each, four conversion pathways were assessed against a fossil fuel reference: (I) anaerobic co-digestion with manure, (II) gasification, (III) combustion in small-to-medium scale biomass combined heat and power (CHP) plants and IV) co-firing in large scale coal-fired CHP plants. Soil carbon changes, direct and indirect land use changes as well as uncertainty analysis (sensitivity, MonteCarlo) were included in the LCA. Results showed that global warming was the bottleneck impact, where only two scenarios, namely willow and Miscanthus co-firing, allowed for an improvement as compared with the reference (-82 and -45 t CO2-eq. ha(-1), respectively). The indirect land use changes impact was quantified as 310 + 170 t CO2-eq. ha(-1), representing a paramount average of 41% of the induced greenhouse gas emissions. The uncertainty analysis confirmed the results robustness and highlighted the indirect land use changes uncertainty as the only uncertainty that can significantly change the outcome of the LCA results.
  • Authors:
    • Blicher-Mathiesen, G.
    • Hoffmann, C. C.
    • Gorres, C. M.
    • Elsgaard, L.
    • Schelde, K.
    • Petersen, S. O.
  • Source: Agriculture Ecosystems & Enviroment
  • Volume: 162
  • Year: 2012
  • Summary: This study presents the first annual estimates of net ecosystem exchange (NEE) of CO 2 and net ecosystem carbon balances (NECB) of contrasting Danish agricultural peatlands. Studies were done at eight sites representing permanent grasslands (PG) and rotational (RT) arable soils cropped to barley, potato or forage grasses in three geo-regional settings. Using an advanced flux-chamber technique, NEE was derived from modelling of ecosystem respiration (ER) and gross primary production (GPP) with temperature and photosynthetically active radiation as driving variables. At PG ( n=3) and RT ( n=5) sites, NEE (meanstandard error, SE) was 5.10.9 and 8.62.0 Mg C ha -1 yr -1, respectively, but with the overall lowest value observed for potato cropping (3.5 Mg C ha -1 yr -1). This was partly attributed to a short-duration vegetation period and drying of the soil especially in potato ridges. NECB, derived from NEE and C-removal in harvested biomass, was equivalent to 8.41.0 and 11.52.0 Mg C ha -1 for the PG and RT land-use types, respectively. Means were not significantly different, P=0.214, and were comparable to a wider range of high-end emission factors for managed organic soils in boreal and temperate climate zones. It was stressed that evaluation of emission factors should explicitly differentiate between data representing net C balance from a soil perspective and CO 2-C balance from an atmospheric perspective. Modelling of inter-annual variability in NEE for three selected sites during a 21-year meteorological period indicated a range of 18-67% (coefficients of variation). Yet, the robustness of these estimates and their importance for the derived emission factors needs to be substantiated experimentally.
  • Authors:
    • Larsen, S. E.
    • Kristensen, K.
    • Elsgard, L.
    • Blicher-Mathiesen, G.
    • Schäfer, C. -M
    • Hoffmann, C. C.
    • Petersen, S. O.
    • Torp, S. B.
    • Greve, M. H.
  • Source: Biogeosciences
  • Volume: 9
  • Issue: 1
  • Year: 2012
  • Summary: The use of organic soils by agriculture involves drainage and tillage, and the resulting increase in C and N turnover can significantly affect their greenhouse gas balance. This study estimated annual fluxes of CH4 and N2O, and ecosystem respiration (R-eco), from eight organic soils managed by agriculture. The sites were located in three regions representing different landscape types and climatic conditions, and three land use categories were covered (arable crops, AR, grass in rotation, RG, and permanent grass, PG). The normal management at each site was followed, except that no N inputs occurred during the monitoring period from August 2008 to October 2009. The stratified sampling strategy further included six sampling points in three blocks at each site. Environmental variables (precipitation, PAR, air and soil temperature, soil moisture, groundwater level) were monitored continuously and during sampling campaigns, where also groundwater samples were taken for analysis. Gaseous fluxes were monitored on a three-weekly basis, giving 51, 49 and 38 field campaigns for land use categories AR, PG and RG, respectively. Climatic conditions in each region during monitoring were representative as compared to 20-yr averages. Peat layers were shallow, typically 0.5 to 1 m, and with a pH of 4 to 5. At six sites annual emissions of N2O were in the range 3 to 24 kg N2O-N ha(-1), but at two arable sites (spring barley, potato) net emissions of 38 and 61 kg N2O-N ha(-1) were recorded. The two high-emitting sites were characterized by fluctuating groundwater, low soil pH and elevated groundwater SO42- concentrations. Annual fluxes of CH4 were generally small, as expected, ranging from 2 to 4 kg CH4 ha(-1). However, two permanent grasslands had tussocks of Juncus effusus L. (soft rush) in sampling points that were consistent sources of CH4 throughout the year. Emission factors for organic soils in rotation and with permanent grass, respectively, were estimated to be 0.011 and 0.47 gm(-2) for CH4, and 2.5 and 0.5 gm(-2) for N2O. This first documentation of CH4 and N2O emissions from managed organic soils in Denmark confirms the levels and wide ranges of emissions previously reported for the Nordic countries. However, the stratified experimental design also identified links between gaseous emissions and site-specific conditions with respect to soil, groundwater and vegetation which point to areas of future research that may account for part of the variability and hence lead to improved emission factors or models.