• Authors:
    • Hermansen, J. E.
    • Chirinda, N.
    • Olesen, J. E.
    • Meyer-Aurich, A.
    • Knudsen, M. T.
  • Source: Journal of Cleaner Production
  • Volume: 64
  • Issue: February
  • Year: 2014
  • Summary: Many current organic arable agriculture systems are challenged by a dependency on imported livestock manure from conventional agriculture. At the same time organic agriculture aims at being climate friendly. A life cycle assessment is used in this paper to compare the carbon footprints of different organic arable crop rotations with different sources of N supply. Data from long-term field experiments at three different locations in Denmark were used to analyse three different organic cropping systems ('Slurry', 'Biogas' and 'Mulching'), one conventional cropping system ('Conventional') and a "No input" system as reference systems. The 'Slurry' and 'Conventional' rotations received slurry and mineral fertilizer, respectively, whereas the 'No input' was unfertilized. The 'Mulching' and 'Biogas' rotations had one year of grass-clover instead of a faba bean crop. The grass-clover biomass was incorporated in the soil in the 'Mulching' rotation and removed and used for biogas production in the 'Biogas' rotation (and residues from biogas production were simulated to be returned to the field). A method was suggested for allocating effects of fertility building crops in life cycle assessments. The results showed significantly lower carbon footprint of the crops from the 'Biogas' rotation (assuming that biogas replaces fossil gas) whereas the remaining crop rotations had comparable carbon footprints per kg cash crop. The study showed considerable contributions caused by the green manure crop (grass-clover) and highlights the importance of analysing the whole crop rotation and including soil carbon changes when estimating carbon footprints of organic crops especially where green manure crops are included. (C) 2013 Elsevier Ltd. All rights reserved.
  • Authors:
    • Peth, S.
    • Mordhorst, A.
    • Horn, R.
  • Source: Geoderma
  • Volume: 219
  • Issue: May
  • Year: 2014
  • Summary: Mechanical disturbance of soil structure is commonly related to altered physical changes in pore systems, which control CO2 effluxes e.g. by changes in gas transport properties and in microbial activity. Soil compaction mostly leads to reduced CO2 fluxes. In contrast, structured soils can also release physically entrapped CO2 or give access to protected carbon sources inside aggregates due to aggregate breakdown by disruptive forces. In this study it was investigated how far arable soil management affects structure- and compaction-related CO2-releases using incubation experiments and CO2 gas analysis under standard matric potentials (-6 kPa). CO2 efflux was analyzed before, during and after mechanical loading using the alkali trap method (static efflux) and a gas flow compaction device (GaFloCoD, dynamic efflux). Intact soil cores (236 and 471 cm(3)) were collected from a Stagnic Luvisol with loamy sand (conservation and conventional tillage systems) and a Haplic Luvisol with clayey silt (under different fodder crops) from the topsoil (10-15 cm) and subsoil (35-45 cm). Mechanical stability was reflected by the pre-compression stress value (P-c) and by the tensile strength of aggregates (12-20 mm). Changes in pore systems were described by air conductivity as well as air capacity and total porosity. While CO2-releases varied highly during the compaction process (GaFloCoD) for different stress magnitudes, soil depths and management systems, basal respiration rates were generally reduced after mechanical loading by almost half of the initial rates irrespective of soil management. For both methods (dynamic and static efflux) restriction in gas transport functionality was proved to have major influence on inhibition of CO2 efflux due to mechanical loading. GaFloCoD experiments demonstrated that decreases in CO2 efflux were linked to structural degradation of pore systems by exceeding internal soil strength (P-c). Otherwise, re-equilibrating matric potentials to 6 kPa and re-incubating offset inhibition of soil respiration suggest a re-enhancement of microbial activity. At this state, physical influences were apparently overlapped by biological effects due to higher energy supply to microbes, which could be offered by spatial distribution changes of microorganisms and organic substrates within a given soil structure. This implies the susceptibility of physical protection mechanism for carbon by disruption of soil structure. In future, special focus should be given on a clear distinction between physical and microbiological effects controlling CO2 fluxes in structured soils. (C) 2014 Elsevier B.V. All rights reserved.
  • Authors:
    • Dalgaard, T.
    • Jorgensen, U.
    • Olesen, J. E.
    • Pugesgaard, S.
  • Source: Renewable Agriculture and Food Systems
  • Volume: 29
  • Issue: 1
  • Year: 2014
  • Summary: Anaerobic digestion of manure and crops provides the possibility of a combined production of renewable energy and organic fertilizer on organic farms and has been suggested as an option to improve sustainability of organic agriculture. In the present study, the consequences of implementation of anaerobic digestion and biogas production were analyzed on a 1000ha model farm with combined dairy and cash crop production, representing organic agriculture in Denmark. The effects on crop rotation, nitrogen flows and losses, yield, energy balance and greenhouse gas (GHG) emissions were evaluated for four scenarios of biogas production on the farm. Animal manure was digested for biogas production in all scenarios and was supplemented with: (1) 100ha grass-clover for biogas, (2) 100ha maize for biogas, (3) 200ha grass-clover for biogas and reduced number of livestock, and (4) 200ha grass-clover for biogas, reduced number of livestock and import of biomass from cuttings made in ungrazed meadows. These four scenarios were compared with the current situation in organic agriculture in Denmark and to a situation where slurry from conventional agriculture is no longer imported. Implementation of anaerobic digestion changed the nitrogen flows on the farm by increasing the slurry nitrogen plant availability and introducing new nitrogen sources from legume-based energy crops or meadows. The amount of nitrogen available for application as fertilizer on the farm increased when grass-clover was used for biogas production, but decreased when maize was used. Since part of the area was used for biogas production, the total output of foodstuffs from the farm was decreased. Effects on GHG emissions and net energy production were assessed by use of the whole-farm model FarmGHG. A positive farm energy balance was obtained for all biogas scenarios, showing that biomass production for biogas on 10% of the farm area results in an energy surplus, provided that the heat from the electricity production is utilized. The energy surplus implies a displacement of fossil fuels and thereby reduced CO2 emission from the farm. Emissions of N2O were not affected substantially by biogas production. Total emissions of methane (CH4) were slightly decreased due to a 17-48% decrease in emissions from the manure store. Net GHG emission was reduced by 35-85% compared with the current situation in organic agriculture. It was concluded that production of biogas on organic farms holds the possibility for the farms to achieve a positive energy balance, provide self-sufficiency with organic fertilizer nitrogen, and reduce GHG emissions.
  • Authors:
    • Dalgaard, R.
    • Petersen, B. M.
    • Oudshoorn, F. W.
    • Halberg, N.
    • Sorensen, C. G.
  • Source: Biosystems Engineering
  • Volume: 120
  • Issue: April
  • Year: 2014
  • Summary: Different tillage systems result in different resource uses and environmental impacts. Reduced tillage generates savings in direct energy input and the amount of machinery items needed. As the basics for holistic Life Cycle Assessments, both the influencing direct and indirect energy as sources of greenhouse gas emissions are required. Life Cycle inventories (LCI) were aggregated for a number of optimised machinery systems and tillage scenarios integrating a four crop rotation consisting of spring barley, winter barley, winter wheat and winter rape seed. By applying Life Cycle Assessments to a number of tillage scenarios and whole field operations sequences, the energy efficiency and environmental impact in terms of greenhouse gas emissions (GHG) were evaluated. Results showed that the total energy input was reduced by 26% for the reduced tillage system and by 41% for the no-tillage system. Energy used for traction and machine construction contributed between 6 and 8% of the total GHG emission per kg product. The total emission of GHG was 915 g CO2 equivalents per kg product by using the conventional tillage system, 817 g CO2 equivalents for the reduced tillage system and 855 g CO2 equivalents for the no tillage system. The no tillage system was expected to yield 10% less. The mineralisation in the soil contributed the most (50-60%) to this emission, while the fertiliser production contributed with 28-33%. The results stress the importance of applying a systems approach to capture the implications of, for example, sustained yields as otherwise the environmental benefits can be compromised. (C) 2014 IAgrE. Published by Elsevier Ltd. All rights reserved.
  • Authors:
    • Don, A.
    • Poeplau, C.
  • Source: GCB Bioenergy
  • Volume: 6
  • Issue: 4
  • Year: 2014
  • Summary: Bioenergy has to meet increasing sustainability criteria in the EU putting conventional bioenergy crops under pressure. Alternatively, perennial bioenergy crops, such as Miscanthus, show higher greenhouse gas savings with similarly high energy yields. In addition, Miscanthus plantations may sequester additional soil organic carbon (SOC) to mitigate climate change. As the land-use change in cropland to Miscanthus involves a C-3-C-4 vegetation change (VC), it is possible to determine the dynamic of Miscanthus-derived SOC (C-4 carbon) and of the old SOC (C-3 carbon) by the isotopic ratio of C-13 to C-12. We sampled six croplands and adjacent Miscanthus plantations exceeding the age of 10 years across Europe. We found a mean C-4 carbon sequestration rate of 0.78 +/- 0.19 Mg ha(-1) yr(-1), which increased with mean annual temperature. At three of six sites, we found a significant increase in C-3 carbon due to the application of organic fertilizers or difference in baseline SOC, which we define as non-VC-induced SOC changes. The Rothamsted Carbon Model was used to disentangle the decomposition of old C-3 carbon and the non-VC-induced C3 carbon changes. Subsequently, this method was applied to eight more sites from the literature, resulting in a climate-dependent VC-induced SOC sequestration rate (0.40 +/- 0.20 Mg ha(-1) yr(-1)), as a step toward a default SOC change function for Miscanthus plantations on former croplands in Europe. Furthermore, we conducted a SOC fractionation to assess qualitative SOC changes and the incorporation of C-4 carbon into the soil. Sixteen years after Miscanthus establishment, 68% of the particulate organic matter (POM) was Miscanthus-derived in 0-10 cm depth. POM was thus the fastest cycling SOC fraction with a C-4 carbon accumulation rate of 0.33 +/- 0.05 Mg ha(-1) yr(-1). Miscanthus-derived SOC also entered the NaOCl-resistant fraction, comprising 12% in 0-10 cm, which indicates that this fraction was not an inert SOC pool.
  • Authors:
    • Greve, M. B.
    • Kheir, R. B.
    • Minasny, B.
    • Hartemink, A. E.
    • Adhikari, K.
    • Greve, M. H.
  • Source: PLOS ONE
  • Volume: 9
  • Issue: 8
  • Year: 2014
  • Summary: Estimation of carbon contents and stocks are important for carbon sequestration, greenhouse gas emissions and national carbon balance inventories. For Denmark, we modeled the vertical distribution of soil organic carbon (SOC) and bulk density, and mapped its spatial distribution at five standard soil depth intervals (0-5, 5-15, 15-30, 30-60 and 60-100 cm) using 18 environmental variables as predictors. SOC distribution was influenced by precipitation, land use, soil type, wetland, elevation, wetness index, and multi-resolution index of valley bottom flatness. The highest average SOC content of 20 g kg(-1) was reported for 0-5 cm soil, whereas there was on average 2.2 g SOC kg(-1) at 60-100 cm depth. For SOC and bulk density prediction precision decreased with soil depth, and a standard error of 2.8 g kg(-1) was found at 60-100 cm soil depth. Average SOC stock for 0-30 cm was 72 t ha(-1) and in the top 1 m there was 120 t SOC ha(-1). In total, the soils stored approximately 570 Tg C within the top 1 m. The soils under agriculture had the highest amount of carbon (444 Tg) followed by forest and semi-natural vegetation that contributed 11% of the total SOC stock. More than 60% of the total SOC stock was present in Podzols and Luvisols. Compared to previous estimates, our approach is more reliable as we adopted a robust quantification technique and mapped the spatial distribution of SOC stock and prediction uncertainty. The estimation was validated using common statistical indices and the data and high-resolution maps could be used for future soil carbon assessment and inventories.
  • Authors:
    • Gundersen, P.
    • Stefansdottir, H. M.
    • Vesterdal, L.
    • Kiar, L. P.
    • Barcena, T. G.
    • Sigurdsson, B. D.
  • Source: Global Change Biology
  • Volume: 20
  • Issue: 8
  • Year: 2014
  • Summary: Northern Europe supports large soil organic carbon (SOC) pools and has been subjected to high frequency of land-use changes during the past decades. However, this region has not been well represented in previous large-scale syntheses of land-use change effects on SOC, especially regarding effects of afforestation. Therefore, we conducted a meta-analysis of SOC stock change following afforestation in Northern Europe. Response ratios were calculated for forest floors and mineral soils (0-10 cm and 0-20/30 cm layers) based on paired control (former land use) and afforested plots. We analyzed the influence of forest age, former land-use, forest type, and soil textural class. Three major improvements were incorporated in the meta-analysis: analysis of major interaction groups, evaluation of the influence of nonindependence between samples according to study design, and mass correction. Former land use was a major factor contributing to changes in SOC after afforestation. In former croplands, SOC change differed between soil layers and was significantly positive (20%) in the 0-10 cm layer. Afforestation of former grasslands had a small negative (nonsignificant) effect indicating limited SOC change following this land-use change within the region. Forest floors enhanced the positive effects of afforestation on SOC, especially with conifers. Meta-estimates calculated for the periods 30 years since afforestation revealed a shift from initial loss to later gain of SOC. The interaction group analysis indicated that meta-estimates in former land-use, forest type, and soil textural class alone were either offset or enhanced when confounding effects among variable classes were considered. Furthermore, effect sizes were slightly overestimated if sample dependence was not accounted for and if no mass correction was performed. We conclude that significant SOC sequestration in Northern Europe occurs after afforestation of croplands and not grasslands, and changes are small within a 30-year perspective.
  • Authors:
    • Porter, J. R.
    • Rasmussen, A.
    • Sanchez, B.
  • Source: Global Change Biology
  • Volume: 20
  • Issue: 2
  • Year: 2014
  • Summary: Because of global land surface warming, extreme temperature events are expected to occur more often and more intensely, affecting the growth and development of the major cereal crops in several ways, thus affecting the production component of food security. In this study, we have identified rice and maize crop responses to temperature in different, but consistent, phenological phases and development stages. A literature review and data compilation of around 140 scientific articles have determined the key temperature thresholds and response to extreme temperature effects for rice and maize, complementing an earlier study on wheat. Lethal temperatures and cardinal temperatures, together with error estimates, have been identified for phenological phases and development stages. Following the methodology of previous work, we have collected and statistically analysed temperature thresholds of the three crops for the key physiological processes such as leaf initiation, shoot growth and root growth and for the most susceptible phenological phases such as sowing to emergence, anthesis and grain filling. Our summary shows that cardinal temperatures are conservative between studies and are seemingly well defined in all three crops. Anthesis and ripening are the most sensitive temperature stages in rice as well as in wheat and maize. We call for further experimental studies of the effects of transgressing threshold temperatures so such responses can be included into crop impact and adaptation models.
  • Authors:
    • Bjornsson,L.
    • Prade,T.
  • Source: Proceedings of the 9th International Conference on Life Cycle Assessment in the Agri-Food Sector
  • Year: 2014
  • Summary: In an analysis of climate effects, increased soil organic carbon will have a dual effect due to both increased soil fertility and carbon sequestration. Even so, soil carbon changes are neglected in many crop production LCAs. In the present study, the introduction of grass-clover crops in cereal-dominated crop production was evaluated. The grass-clover crops were used for biogas production, and the digested residue was recycled to the farm as biofertilizer. A shift from the cereal-dominated crop rotation to integrated production of food crops and one or two years of grass-clover crops used as biogas feedstock would result in avoided emissions of 2-3 t CO 2-eq. ha -1 a -1. Integrated food and energy crop production would in this case improve soil organic carbon content at the same time as resulting in considerably decreased greenhouse gas emissions from the cultivation system.
  • Authors:
    • Smith, P.
    • Williams, M.
    • Forristal, D.
    • Lanigan, G.
    • Osborne, B.
    • Abdalla, M.
    • Jones, M. B.
  • Source: Soil Use and Management
  • Volume: 29
  • Issue: 2
  • Year: 2013
  • Summary: Conservation tillage (CT) is an umbrella term encompassing many types of tillage and residue management systems that aim to achieve sustainable and profitable agriculture. Through a global review of CT research, the objective of this paper was to investigate the impacts of CT on greenhouse gas (GHG) emissions. Based on the analysis presented, CT should be developed within the context of specific climates and soils. A number of potential disadvantages in adopting CT practices were identified, relating mainly to enhanced nitrous oxide emissions, together with a number of advantages that would justify its wider adoption. Almost all studies examined showed that the adoption of CT practices reduced carbon dioxide emissions, while also contributing to increases in soil organic carbon and improvements in soil structure.