FIBL: Climate change mitigation is urgent, and adaptation to climate change is crucial, particularly in agriculture, where food security is at stake. Agriculture, currently responsible for 20-30% of global greenhouse gas emissions (counting direct and indirect agricultural emissions), can however contribute to both climate change mitigation and adaptation. The main mitigation potential lies in the capacity of agricultural soils to sequester CO2 through building organic matter.

This potential can be realized by employing sustainable agricultural practices, such as those commonly found within organic farming systems. Examples of these practices are the use of organic fertilizers and crop rotations including legume leys and cover crops. Mitigation is also achieved in organic agriculture through the avoidance of open biomass burning, and the avoidance of synthetic fertilizers, the production of which causes emissions from fossil fuel use.

Common organic practices also contribute to adaptation. Building soil organic matter increases water retention capacity, and creates more stabile, fertile soils, thus reducing vulnerability to drought, extreme precipitation events, floods and water logging. Adaptation is further supported by increased agro-ecosystem diversity of organic farms, based on management decisions, reduced nitrogen inputs and the absence of chemical pesticides. The high diversity together with the lower input costs of organic agriculture is key to reducing production risks associated with extreme weather events.

All these advantageous practices are not exclusive to organic agriculture. However, they are core parts of the organic production system, in contrast to most non-organic agriculture, where they play a minor role only.

Mitigation in agriculture is however not restricted to the agricultural sector alone. Consumer preferences for products from conventional or organic farms, seasonal and local production, pest and disease resistant varieties, etc. strongly influence agricultural production systems, and thus the overall mitigation potential of agriculture. Even more influential are meat consumption and food wastage. Any discussion on mitigation of climate change in agriculture thus needs to address the entire food chain, and to be linked to general sustainable development strategies.

The main challenges to dealing appropriately with the climate change mitigation and adaptation potential of organic agriculture, and agriculture in general, stem from

1. insufficient understanding of some of the basic processes, such as the interaction of N2O emissions and soil carbon sequestration, contributions of roots to soil carbon sequestration, and the life-cycle emissions of organic fertilizers, such as compost;
2. b) lack of procedures for emissions accounting which adequately represent agricultural production systems with multiple and diverse outputs, which also encompass ecosystem services;
3. c) the problem to identify and design adequate policy frameworks for supportingmitigation and adaptation in agriculture, i.e. such that do not put systemic approaches at a disadvantage due to difficulties in the quantification of emissions, and in their allocation to single products;
4. d) the necessity to assure that the current focus on mitigation does not lead to neglect of other factors influencing the sustainability of agriculture, such as pesticide loads, eutrophication, acidification or soil erosion; and
5. e) the open questions, how to address consumer behaviour and how to further changes in consumption patterns, in order to utilize their mitigation potential.

The goal of this text is to provide a timely, short, understandable but nonetheless comprehensive and critical overview of the links between organic agri-culture and climate change. It outlines the mitiga-tion and adaptation potential of organic agriculture and addresses main opportunities, challenges, insti-tutional and policy aspects, thus placing this dis-cussion in a broader context, which also addresses consumer aspects and policies. For further details see the references given in the text and Kotschi and Müller-Sämann, 2004; Niggli et al., 2007, 2009; El-Hage Scialabba and Müller-Lindenlauf, 2010; Mul-ler et al., 2011; Muller and Aubert, forthcoming; Muller et al., forthcoming.

MITIGATION

1. Maintaining and increasing soil organic carbon in agricultural systems is the option with the largest mitigation option in agriculture (Smith et al., 2008). Organic agriculture (OA) has a significant potential contribution in this respect: practices that are commonly used on organic farms (use of organ-ic fertilizers, fertility building leys with legumes and cover crops) further the production of soil or-ganic matter (Smith et al., 2008; Leifeld and Fuhrer, 2010, Chirinda et al. 2010a).
2. Organic agriculture has lower N2O emissions from nitrogen application, due to lower overall ni-trogen input per ha than in conventional agriculture (Mäder et al., 2002, Olesen et al. 2006). In those cases, where the yields are lower on organic farms, comparisons made per kg of product are less fa-vourable for organic systems (Chirinda et al., 2010b) unless N use efficiency is higher on organic farms (cf. 4 below). The type of N input and how it is managed most likely plays a considerable role for N2O emissions, but much still needs to be un-derstood regarding the role of N inputs in organic form.
3. Open burning of crop residues and biomass waste is prohibited for agriculture in most industri-alized countries, but it is still common practice in conventional agriculture in many developing coun-tries. In organic agriculture, biomass is not burned, but recycled to the soil to improve fertility. This re-duces the CH4 and N2O emissions in comparison to conventional agriculture, where crop residues are often burnt on the field (Smith et al., 2007)
4. Conventional stockless arable farms depend on the input of synthetic nitrogen fertilizers, while stockpiled manure and slurry on livestock farms create additional emissions and other environmen-tal problems. Organic farms mitigate such problems by on-farm or cooperative use of farmyard manure between crop and livestock operations (El-Hage Scialabba and Müller-Lindenlauf 2010). In particu-lar where this leads to an overall increase in N us efficiency, the result is a reduction in emissions per kg of product (Olesen et al., 2006).
5. Due to reduced concentrate feed use in rumi-nant animal husbandry, organic animal agricul-ture causes less direct land use change (deforesta-tion to gain cropland for concentrate feed produc-tion) and thus also less CO2 emission from soil car-bon losses due to this change. Since organic grass-land and fodder production is often equally produc-tive as with conventional systems there are little in-direct land use change effects. On the other hand, higher roughage diets can lead to higher methane emissions from ruminants (Shibata and Terada, 2010). The net effect of increased roughage none-theless yields an overall reduction in emissions. Research comparing ruminant livestock production systems also shows that organic farming systems perform favourably, in terms of energy use, due to energy savings associated with reliance on clover-grass leys and high forage/low cereal diets (Lamp-kin, 2007). In addition, animal welfare is improved, as a high roughage diet is more natural for rumi-nants (Zollitsch et al., 2004). Furthermore in-creased longevity within organic systems reduces the relative emissions from the unproductive rear-ing phase of dairy cows (Lynch et al., 2011).
6. Ca. 1% of global fossil energy consumption is used for chemical nitrogen fertilizer production. Organic agriculture does not contribute to these emissions, as no chemical nitrogen fertilizers are used. In organic agriculture, nitrogen input stems from the use of nitrogen fixing leguminous plants and the application of manure and compost. Bio-logical N fixation is not in itself a source of N2O (Rochette and Janzen, 2005 ), but soil incorporation of N-rich plant residues from legume crops can lead to high emissions of N2O (Moller and Stinner, 2009). More research is however needed to deter-mine the relative performance of organic vs. chem-ical fertilizers, based on lifecycle emissions and in-cluding interactions with soil carbon levels. To give justice to the systemic aspects of organic agricul-ture, one needs to go beyond the mere comparison of fertilizer types. The fact that organic systems are based on lower nitrogen inputs, closed nutrient cy-cles and combined animal and plant production needs to be accounted for, and this requires a holis-tic perspective on the accounting of greenhouse gas emissions from farming systems. Furthermore, there are strong indications from many cases that application of synthetic nitrogen fertilizers can lead to losses of soil organic matter (Khan et al. 2007, Mulvaney et al. 2009). Generalisation of these find-ings is however discussed controversially (Ladha et al. 2011; see also the various comments and replies on the two articles mentioned above).

Authors: Adrian Muller, Joergen Olesen, Joan Davis, Laurence Smith, Karolína Dytrtová, Andreas Gattinger, Nic Lamp-kin, Urs Niggli

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