Department of Plant Sciences

There is growing concern that greenhouse gas (GHG) emissions during agricultural energy crop production might negate GHG emission savings. Here a study is presented evaluating two favourable biogas crops in two agro-ecological regions of Northern Germany for their productivity and GHG emissions. A 2-year field experiment was conducted at two sites with different soil type but similar temperate maritime climate. We compared silage maize which is currently the standard crop grown for biogas fermentation purposes to an alternative bioenergy crop at each site. Three forms of fertilizers/manures were given: calcium ammonium nitrate, cattle / pig slurry, biogas waste. GHG emissions of all biogas crops were strongly dominated by N2O emissions. There were very short CH4 emission events immediately after application of slurry and biogas waste. N2O flux patterns usually followed fertilizer application events in all crops and at both sites. Flux patterns indicated pronounced effects of soil moisture which was also seen as responsible for the 20–30 % higher N2O fluxes in maize compared to the other tested crops. Overall, N2O emissions at the loamy soil site were at least 3 times higher than in all crops examined at the site with sandy soil. The present study provides a very good basis for the assessment of direct emissions of greenhouse gases from relevant biogas crops in North-West Europe. It is intended to use measured and simulated data on soil moisture and the N/C inputs by fertilizer/manure application as drivers for a nitrification/denitrification module linked to a crop growth model.