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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2018-455
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2018-455
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Reviews and syntheses 27 Nov 2018

Reviews and syntheses | 27 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Review of key causes and sources for N2O emissions and NO3-leaching from organic arable crop rotations

Sissel Hansen1, Randi Berland Frøseth2, Maria Stenberg3, Jarosław Stalenga4, Jørgen E. Olesen5, Maike Krauss6, Paweł Radzikowski4, Jordi Doltra7, Shahid Nadeem8, Torfinn Torp9, Valentini Pappa10, and Christine A. Watson11,12 Sissel Hansen et al.
  • 1Norwegian Centre for Organic Agriculture, 6630 Tingvoll, Norway
  • 2Department of Grain and Forage Seed Agronomy, Norwegian Institute of Bioeconomy (NIBIO), 1431 Ås, Norway
  • 3Department of Soil and Environment, Swedish University of Agricultural Sciences (SLU), Skara, Sweden
  • 4Department of Systems and Economics of Crop Production, Institute of Soil Science and Plant Cultivation - State Research Institute, 24-100 Puławy, Poland
  • 5Department of Agroecology, Aarhus University, 8830 Tjele, Denmark
  • 6Department of Soil Sciences, Research Institute of Organic Agriculture (FiBL), 5070 Frick, Switzerland
  • 7Cantabrian Agricultural Research and Training Centre, CIFA, 39600 Muriedas, Cantabria, Spain
  • 8Department for Feed and livestock, Norwegian Institute of Bioeconomy (NIBIO), 1431 Ås, Norway
  • 9Department of Research, Norwegian Institute of Bioeconomy (NIBIO), 1431 Ås, Norway
  • 10Texas A&M, Energy Institute, College Station, TX 77845-3372, USA
  • 11Department of Crop Production Ecology, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden
  • 12SRUC, Craibstone Estate, Aberdeen, AB21 9YA, UK

Abstract. The emissions of nitrous oxide (N2O) and leaching of nitrate (NO3) have considerable negative impacts on climate and the environment. Although these environmental burdens are on average less per unit area in organic than in non-organic production, they are not smaller per unit of product. If organic farming is to maintain its goal of being an environmentally friendly production system, these emissions should be mitigated. We discuss the impact of possible triggers within organic arable farming practice for the risk of N2O emissions and NO3 leaching under European climatic conditions, and possible strategies to reduce these. Organic arable crop rotations can be characterised as diverse with frequent use of legumes, intercropping and organic fertilizers. The soil organic matter content and share of active organic matter, microbial and faunal activity are higher, soil structure better and yields lower, than in non-organic, arable crop rotations. Soil mineral nitrogen (SMN), N2O emissions and NO3 leaching are low under growing crops, but there is high potential for SMN accumulation and losses after crop termination or crop harvest. The risk for high N2O fluxes is increased when large amounts of herbage or organic fertilizers with readily available nitrogen (N) and carbon are incorporated into the soil or left on the surface. Freezing/thawing, drying/rewetting, compacted and/or wet soil and mixing with rotary harrow further enhance the risk for high N2O fluxes. These complex soil N dynamics mask the correlation between total N-input and N2O emissions from organic arable crop rotations. Incorporation of N rich plant residues or mechanical weeding followed by bare fallow increases the risk of nitrate leaching. In contrast, strategic use of deep-rooted crops with long growing seasons in the rotation reduces nitrate leaching risk. Reduced tillage can reduce N leaching if yields are maintained. Targeted treatment and use of herbage from green manures, crop residues and catch crops will increase N efficiency and reduce N2O emissions and NO3 leaching. Continued regular use of catch crops has the potential to reduce NO3 leaching but may enhance N2O emissions. A mixture of legumes and non-legumes (for instance grasses or cereals) are as efficient a catch crop as monocultures of non-legume species.

Sissel Hansen et al.
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Short summary
Soil mineral nitrogen, nitrous oxide emissions and nitrate leaching are low under growing crops in organic arable crop rotations, but large losses may occur after crop termination. Continued regular use of catch crops has the potential to reduce nitrate leaching but may enhance nitrous oxide emissions. Mixtures including legumes are as efficient catch crops as monocultures of non-legumes. Good soil aeration and restricted incorporation of plant material will reduce nitrous oxide fluxes.
Soil mineral nitrogen, nitrous oxide emissions and nitrate leaching are low under growing crops...
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