Emission of N2O from Biogas Crop Production Systems in Northern Germany

There is a growing concern that greenhouse gas (GHG) emissions during agricultural energy crop production might negate GHG emission savings which was not intended when promoting the use of renewable energy. Nitrous oxide (N2O) is a major GHG, and in addition, it is the most powerful ozone-depleting compound that is emitted by human activity. The use of N fertilizers and animal manures is the main anthropogenic source of N2O emissions. In spite of their high relevance, we still have limited understanding of the complex underlying microbial processes that consume or produce N2O and their interactions with soil types, fertilizers (rate and types), plants, and other environmental variables. In a 2-year field experiment, we compared two important biogas crops in two different agro-ecological regions of northern Germany for their productivity and GHG emissions, using the closed-chamber technique and high time-resolution sampling. Silage maize, which is currently the most widespread crop grown for biogas fermentation purposes in Germany, was compared with an alternative bioenergy crop at each site. The three forms of nitrogen fertilizers/manures were given: calcium ammonium nitrate, cattle/pig slurry, and biogas residue. The greatest N2O flux activity occurred in the period of May–July in all crops and at both sites. Flux patterns indicated pronounced effects of soil moisture-soil mineral-N interactions which were also seen as causation of the higher N2O fluxes in the bioenergy crop maize compared to the other tested energy crops. ...