With its atmospheric half-life time of 113 years, nitrous oxide (N2O) is a potent greenhouse gas which contributes to the ozone layer destruction. Agriculturally managed soils hold for the gross of anthropogenic N2O release. In order to develop effective mitigation strategies, a detailed understanding of processes and mechanisms leading to N2O formation and reduction in croplands is urgently needed. Although the influence of single parameters on N2O emissions is relatively well understood, knowledge on the underlying mechanisms especially under complex farming systems is still sparse. As N-transformation processes in soils are almost entirely controlled by microbial activity, the understanding of the factors influencing abundance and activity of functional microbial communities is crucial. Special interest is addressed to the last step of the denitrification chain, the reduction of N2O to N2, as it may define the overall function of soils as source or sink for N2O. In this project, the impact of tillage (reduced vs. conventional) and fertilization systems (biodynamic vs. organic vs. conventional) on N-cycling microbial communities are investigated in addition to long term N2O measurements in established field trials.
N2O is a major greenhouse gas, which also contributes to ozone layer destruction. Due to its long atmospheric half lifetime its global warming potential exceeded that of CO2 around 300 times. As N2O is produced and reduced by soil microorganisms during N-transformation processes, croplands cause the biggest share of anthropogenic N2O emissions.
n order to develop effective mitigation strategies for N2O emissions it is essential to develop a deeper understanding of controls and mechanisms influencing N20 emissions. Although there is a good knowledge basis on single parameters influencing GHG emission from soils, only little is known about how complex farming systems (conventional vs. organic management, tillage, fertilization) influence GHG fluxes in croplands. As N-transformation processes in soils are almost entirely controlled by microbial activities it is crucial to understand the factors influencing abundance and activity of functional microbial communities. This is especially valid for the reduction of N2O to N2 representing the last step of denitrification. The extent of this process determines the overall function of soils as sources or sinks for N2O. As one third of the known denitrifying bacteria lack the genetic capability of performing this reaction, the structure of the denitrifying microbial community is of great importance.
In order to investigate how soil management strategies impact functional N transforming microbial communities, research on well-established field trials is conducted. The DOK trial in Therwil/CH serves as research platform to investigate effects of conventional and organic farming systems. In the field trial in Frick/AG, the impact of reduced and conventional tillage is investigated. Furthermore the impact of biochar addition in investigated in a field trial established 2013 in Reckenholz.
Analyses of N-transforming microbial communities on a structural and functional level are complementing ongoing, long-term N2O measurements. Abundance and activity of these communities are quantified using the qPCR approach. Furthermore the 15N tracer technique is used to determine sources of N2O geochemically. We expect that by combining geochemical and molecular-biological methods new insights on mechanisms of N2O production and reduction will be revealed.
