Nitrous oxide : Effects of soil management on soil micro-organisms that form and decompose nitrous oxide

Agricultural soils represent an important source of nitrous oxide that has a strong effect on the climate. The “Nitrous oxide” project examined the role of microbial communities regarding production and decomposition of nitrous oxide in the soil, and how agricultural practices affect these micro-organisms.

  • Background (completed research project)

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    Nitrous oxide can be produced and degraded by microorganisms in the soil and it has a strong impact on the climate. The research was based on field trials covering distinct soil management practices that are currently being debated in agricultural research: the Frick long-term trial on reduced tillage, the DOK long-term trial on farming systems and a newly established field trial on biochar. In field and laboratory experiments, nitrous oxide emissions and functional microbial communities were quantified after the fertilisers had been added.

  • Aim

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    The project aimed at delivering basic knowledge on the impact of soil management on the structure and function of the microbial communities. The project aimed at determining the impact of soil management strategies on nitrous oxide emissions; evaluating the impact of soil management strategies on functional microbial communities during nitrous oxide production and reduction; assessing to what extent functional gene analyses can explain nitrous oxide emissions.

  • Results

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    Among the three investigated soil management practices (tillage; farming system; biochar), biochar application seemed to bring about the strongest reduction in nitrous oxide in agricultural soils. In all investigated soils, the reduction of nitrous oxide (N2O) to nitrogen (N2) was an important nitrogen transformation process and in biochar-amended soils it was the key process.

    Keeping pH of agricultural soils above 6 will help to retain the functionality of nitrous oxide consuming bacteria and thus support climate smart agricultural practices.

    Soils rich in organic carbon tended to have an increased nitrous oxide emission potential. Adapted fertilisation strategies are therefore crucial for maintaining climate smart agriculture. This includes the timing of fertilisation as well as the amount and type of fertiliser.

    The expression of functional genes could serve as a general indication of nitrification and denitrification activity but, except for biochar, there were no variations between treatments. This was presumably due to spatial and temporal heterogeneity in the field.

    Knowledge about the structure and functions of soil microbial communities helps to enhance the sustainable use of soils and agricultural inputs such as fertilisers.

  • Implications for research

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    The project will contribute to a better understanding of the functional role of microbial diversity. In particular, the project provides basic information on the variations observed in nitrous oxide fluxes in the field and on the possible impact of soil management in this context.

    The Swiss DOK trial is one of the few long-term field trials worldwide that can present a comprehensive nitrous oxide balance at the field level backed up by detailed process studies. This project will further strengthen its reputation. It will also strengthen the competitiveness of research in Switzerland by linking established soil ecological research methods with cutting-edge techniques in molecular biology.

    The project also addresses the “Forschungskonzept Umwelt für die Jahre 2013-2016” of the Federal Office for the Environment, where research gaps in soil biodiversity and its functions are explicitly identified.

  • Implications for practice

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    The project provides detailed information on the key factors in soil-derived nitrous oxide emissions and the role of soil microbial communities. It describes the impact of different agricultural practices in this regard. This project and other ongoing projects worldwide provide data that is urgently needed to evaluate biochar application as a possible alternative management option in temperate agriculture.

    The results will help to identify the main drivers of soil-derived nitrous oxide emissions and to meet one of the goals of the strategy against greenhouse gas emissions in agriculture devised by the Federal Office for Agriculture (FOAG). The project also contributes to the implementation of the strategy of the FOAG on soil protection and cultivation by closing knowledge gaps with regard to reduced tillage. Moreover, the project is linked to the “Soil Thematic Strategy” of the European Commission, in which conservation tillage practices are explicitly addressed to reduce greenhouse gas emissions and stop erosion.

  • Original title

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    Structure and function of N2O producing and reducing microbial communities as influenced by soil management