Mitteilungen der Gesellschaft für Pflanzenbauwissenschaften Band 23

Mitt. Ges. Pflanzenbauwiss. 23: 43–44 (2011)
Processes and drivers of N2O emissions from soils
after application of organic fertilizers such as biogas residues
Mehmet Senbayram 1,2 , Jan Reent Köster 1 , Karl H. Mühling 1 and Klaus Dittert 1,3
1 Institute of Plant Nutrition and Soil Science, Christian-Albrechts-University Kiel; 2 Present address:
Hanninghof Research Center, Yara GmbH & Co. KG, Dülmen; 3 Present address: Plant Nutrition and
Crop Physiology, Department of Crop Sciences, University of Göttingen. E-Mail:
khmuehling@plantnutrition.uni-kiel.de
Introduction
Greenhouse gas (GHG) emissions during agricultural production of energy crops are
a serious constraint to one of the central aims of bioenergy production: reducing CO2
emissions by reducing fossil fuel consumption. The biogas fermentation process
produces substantial amounts of fermentation effluents, also called biogas residues
(BGR), that may serve as nutrient source for agricultural production but that are also
a new source of GHG emissions. Therefore the present study aimed at evaluating
favorable biogas crops (maize, wheat and grassland) in two agro-ecological regions
of Northern Germany for their productivity and their environmental impact. We
focused on nitrous oxide, carbon dioxide, and methane fluxes from soil with various
rates and types of nitrogen fertilizers. The objectives of our study were i) obtaining
year-round trace gas flux data of biogas crops, and ii) evaluating effects after
application of biogas residues as manure in comparison to other organic and mineral
fertilizers. Attribution of nitrous oxide (N2O) emission to organic and inorganic N
fertilizers requires understanding of how these inputs affect the two biological N2O
generating processes, i.e. denitrification and nitrification. Therefore, we setup three
additional pot trials in order to study these relationships.
Materials and Methods
A two-year field experiment was conducted at two sites with different soil type and
soil fertility but similar temperate maritime climate (ø 684 mm, 9.0°C). Site one was
characterized by its Luvisol soil with sandy loam texture and the soil type at the
second site was a gleyic Podzol derived from glacio-fluvial deposits of the last
glaciation with a texture being dominated by sand. As silage maize is currently the
standard crop grown for biogas fermentation purposes, we compared silage maize to
alternative bioenergy-crops. Thus at site one, we evaluated trace gas fluxes from
silage maize and wheat (whole crop) - Italian ryegrass (catch crop) rotation that was
grown in parallel plots (12 x 12 m) with both main crops in both years. At site two,
maize monoculture was compared to a four-cut silage grass system. We evaluated
three levels of nitrogen fertilizer rates (0, 120, 360 kg N ha -1 for maize and wheat; 0,
160, 480 kg N ha -1 for grassland), with the highest level - chosen for modeling purposes
- being clearly beyond recommended rates. Three forms of fertilizers/manures
were given: calcium ammonium nitrate, cattle / pig slurry, biogas residue. Fertilizers
were applied in 2 to 4 split dressings. In the pot experiments, we compared mineral N
(ammonium sulfate) and biogas residues for their effects on N2O fluxes using either
stable isotope labeling or N2O isotopomer measurements for differentiation of nitrification
and denitrification-derived N2O emission. In another experiment we tested the
effect of more than 40 years of organic fertilizer application on the denitrification
potential of soils and the denitrification product stoichiometry (N2O / N2 ratio) by using
an anoxic incubation system.