2 results
Biogas in organic agriculture—effects on productivity, energy self-sufficiency and greenhouse gas emissions
- Siri Pugesgaard, Jørgen E. Olesen, Uffe Jørgensen, Tommy Dalgaard
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- Journal:
- Renewable Agriculture and Food Systems / Volume 29 / Issue 1 / March 2014
- Published online by Cambridge University Press:
- 24 January 2013, pp. 28-41
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- Article
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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 1000 ha 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) 100 ha grass–clover for biogas, (2) 100 ha maize for biogas, (3) 200 ha grass–clover for biogas and reduced number of livestock, and (4) 200 ha 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.
11 - Nitrogen flows and fate in rural landscapes
- from Part III - Nitrogen flows and fate at multiple spatial scales
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- By Pierre Cellier, INRA, France, Patrick Durand, INRA, France, Nick Hutchings, University of Aarhus, Ulli Dragosits, Centre for Ecology and Hydrology, Mark Theobald, Technical University of Madrid/Centre for Ecology and Hydrology, Jean-Louis Drouet, INRA, France, Oene Oenema, Wageningen University and Research Centre, Albert Bleeker, Energy Research Centre of the Netherlands, Lutz Breuer, Institute for Landscape Ecology and Resources Management, Tommy Dalgaard, Aarhus University, Sylvia Duretz, INRA, France, Johannes Kros, Alterra, Wageningen University and Research Centre, Benjamin Loubet, UMR Environm & Grandes Cultures, Joergen Eivind Olesen, Aarhus University Department of Agroecology and Environment, Philippe Mérot, INRA, France, Valérie Viaud, INRA, France, Wim de Vries, Wageningen University and Research Centre, Mark A. Sutton, Centre for Ecology and Hydrology
- Edited by Mark A. Sutton, NERC Centre for Ecology and Hydrology, UK, Clare M. Howard, NERC Centre for Ecology and Hydrology, UK, Jan Willem Erisman, Gilles Billen, Albert Bleeker, Peringe Grennfelt, Hans van Grinsven, Bruna Grizzetti
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- Book:
- The European Nitrogen Assessment
- Published online:
- 16 May 2011
- Print publication:
- 14 April 2011, pp 229-248
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Summary
Executive summary
Nature of the problem
The transfer of nitrogen by either farm management activities or natural processes (through the atmosphere and the hydrological network) can feed into the N cascade and lead to indirect and unexpected reactive nitrogen emissions.
This transfer can lead to large N deposition rates and impacts to sensitive ecosystems. It can also promote further N2O emission in areas where conditions are more favourable for denitrification.
In rural landscapes, the relevant scale is the scale where N is managed by farm activities and where environmental measures are applied.
Approaches
Mitigating nitrogen at landscape scale requires consideration of the interactions between natural and anthropogenic (i.e. farm management) processes.
Owing to the complex nature and spatial extent of rural landscapes, experimental assessments of reactive N flows at this scale are difficult and often incomplete. It should include measurement of N flows in the different compartments of the environment and comprehensive datasets on the environment (soils, hydrology, land use, etc.) and on farm management.
Modelling is the preferred tool to investigate the complex relationships between anthropogenic and natural processes at landscape scale although verification by measurements is required. Up to now, no model includes all the components of landscape scale N flows: farm functioning, short range atmospheric transfer, hydrology and ecosystem modelling.