Management options to lower N2O emissions can be derived from the presented experiments. For example, the incubation experiment suggests avoiding N fertilizer application to post-harvest soils with a high availability of residue-C.
Mitigation options from the presented experiments can be derived from high N2O emissions events. The amount of N fertilizer should be closely related to the N demand of the respective crop to reduce soil mineral N concentrations. Several studies (Kim et al., 2013, Shcherbak et al., 2014) demon-strated a linear relation of N fertilizer rate and N2O emissions as long as plant demand was satisfied whereas an N surplus led to non-linear and over proportionally high N2O emissions. Especially, N fer-tilizer rates above plant demand led to an exponential response of N2O emissions. This highlights the importance for a precise calculation of N application.
To maintain a supply of mineral N forms to plants nitrification inhibitors (NI) are discussed re-cently. NIs are chemical substances, like 3,4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD), also several others are commercially produced. As NIs differ in their chemical structure, the biochemical processes diverge. NIs modify the soil N cycling by blocking the first enzymatic step of
Figure 5.4 Climate conditions at the site Merbitz in the years a 2013 and 2014. Pictures were taken in the beginning of April in the respective years (2013: April 8th, 2014: April 10th).
less NOx species. Especially NO3 is mobile in the soil and prone to leaching. NO3 is also a substrate for denitrification. Wu et al. (2017) showed that a high NH4 concentration with the addition of a C source (wheat straw) to soil led to high N2O emissions. The NO3 concentration was lower in the treatment with a NI. The N2O emissions were decreased by 40% when adding a NI to straw amended soil. Although, the long-term effect of NIs is not clear yet, studies should focus on NIs and their effect on post-harvest NO3 concentrations under field conditions. Here, data sets of a full year with measurements are needed to be able to evaluate the effectiveness under specific conditions (Ruser and Schulz, 2015).
5.7 References
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Congreves, K.A., Hooker, D.C., Hayes, A., Verhallen, E.A., van Eerd, L.L., 2017. Interaction of long-term nitrogen fertilizer application, crop rotation, and tillage system on soil carbon and nitrogen dynamics. Plant Soil 410 (1-2), 113–127. 10.1007/s11104-016-2986-y.
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Gan, Y.T., Liang, B.C., Liu, L.P., Wang, X.Y., McDonald, C.L., 2011. C:N ratios and carbon distribu-tion profile across rooting zones in oilseed rape and pulse crops. Crop Pasture Sci. 62 (6), 496.
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Garcia-Marco, S., Ravella, S.R., Chadwick, D., Vallejo, A., Gregory, A.S., Cardenas, L.M., 2014. Rank-ing factors affectRank-ing emissions of GHG from incubated agricultural soils. Eur. J. Soil Sci. 65 (4), 573–583. 10.1111/ejss.12143.
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Increasing crop diversity mitigates weather variations and improves yield stability. PloS one 10 (2), 1–20. 10.1371/journal.pone.0113261.
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Kim, D.-G., Hernandez-Ramirez, G., Giltrap, D., 2013. Linear and nonlinear dependency of direct ni-trous oxide emissions on fertilizer nitrogen input: A meta-analysis. Agric., Ecosyst. Environ. 168, 53–65. 10.1016/j.agee.2012.02.021.
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Shcherbak, I., Millar, N., Robertson, G.P., 2014. Global metaanalysis of the nonlinear response of soil nitrous oxide (N2O) emissions to fertilizer nitrogen. Proceedings of the National Academy of Sci-ences of the United States of America 111 (25), 9199–9204. 10.1073/pnas.1322434111.
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I am indebted to Prof. Dr. Klaus Dittert who made this thesis possible and assigned me to the project
“Minderung von Treibhausgasemissionen im Rapsanbau unter besonderer Berücksichtigung der Stick-stoffdüngung”. I am thankful to him for guiding my research for the past four years, the constant sup-port, friendly supervision and critical reading of abstracts and manuscripts.
I am grateful to my supervisor Prof. Dr. Mehmet Senbayram, who has brought me in touch with gas chromatography and giving me enthusiastically helpful advices not only technical, but also on all other questions concerning agricultural research and manuscript writing.
I also thank Dr. Reiner Ruser for his willingness to be member of the examination board.
I am grateful for the patient assistance in data management, statistics and manuscript writing given by Dr. Roland Fuß.
I thank Prof. Dr. Olaf Christen and Hannes Hegewald for the fruitful cooperation.
I thank Dr. Birgit Pfeiffer for discussion of results during meetings and her kind support in difficult questions.
I also thank Dr. Bernd Steingrobe for discussion and manuscript reading even when time was short.
I thank Christiane, Simone, Marlies, Jürgen, Reinhard, Susanne, Kirsten, Ulrike and Ute for the assis-tance and helpful advices in administrative, lab and field issues.
I highly appreciate the help of my student assistants Matthias, Jannike and Henrik. They always had a helping hand for field work, lab analyses and data preparation even on short notice.
I also highly appreciated the conversations with my fellow phd students Merle, Ershad, Balint, Annika, Pauline and Florian who initially converted me to a coffee drinker.
I also thank the section Plant Nutrition and Yield Physiology, the IAPN and the section Quality of Plant Products for welcoming my dog Pepper when she joined me. She enjoyed her time with lots of attention and goodies.
This study was funded by the Agency for Renewable Resources and the Union for the promotion of oil and protein plants; the financial support is gratefully acknowledged.
Peer-reviewed Publications
Köbke S, Senbayram M, Pfeiffer B, Dittert K (2018): Post-harvest N2O emissions related to plant residue incorporation (oilseed rape and barley straw) depends on soil NO3- content. Soil & Tillage Research Soil and Tillage Research 179, pp. 105-113.
Ruser R, Fuß R, Andres M, Hegewald H, Kesenheimer K, Köbke S, Räbiger T, Suarez Quinones T, Augustin J, Christen O, Dittert K, Kage H, Lewandowski I, Prochnow A, Stichnothe H, Flessa H:
Nitrous oxide emissions from winter oilseed rape cultivation. Submitted to Agriculture, Ecosystems and Environment.
Pietzner B, Rücknagel J, Koblenz B, Bednorz D, Tauchnitz N, Bischoff J, Köbke S, Meurer K, Meißner R, Christen O (2017): Impact of slurry strip-till and full-surface slurry incorporation on NH3 and N2O emissions on different plot trials in Central Germany. Soil & Tillage Research 169.
Senbayram M, Wenthe C, Lingner A, Isselstein J, Steinmann H-H, Köbke S (2016): Legume-based mixed intercropping systems may lower agricultural born N2O emissions. Energy, Sustainability and Society 6(2).
Conference Contributions
Oral Presentations
Köbke S, Kesenheimer K, Räbiger T, Andres M, Hegewald H, Suarez T, Fuß R (2015): Yield-scaled N2O emissions of oilseed rape bioenergy crop rotations in Germany; International Workshop “Green-house gas emission from oilseed rape cropping and mitigation options” in Braunschweig, Germany.
Köbke S, Senbayram M, Hegewald H., Christen O, Dittert K (2015): Post-harvest N2O emissions in soils planted with oilseed rape were not affected by the quality of incorporated straw; European Geo-sciences Union General Assembly 2015 in Vienna, Austria. Application for funding and conference grant received from Göttingen International.
Poster Presentations
Köbke S, Senbayram M, Dittert K (2014): Biochemical variations in plant residues (oilseed rape and barley straw) affect N2O emissions and organic matter decomposition rate; 18th Nitrogen Workshop in Lisboa, Portugal.
Köbke S, Senbayram M, Hegewald H, Christen O, Dittert K (2014): Post-harvest N2O emissions from oilseed rape fields do not differ from cereals; International Conference of the German Society of Plant Nutrition in Halle (Saale), Germany.
share of post-harvest N2O emissions – Experiments with oilseed rape & barley straw –NORA-ICOS-SITES workshop "Gas flux measurements in terrestrial ecosystems - state of the art and emerging technologies" in Gothenborg, Sweden.
Göttingen, March 2017
1. Hiermit erkläre ich, dass diese Arbeit weder in gleicher noch in ähnlicher Form bereits anderen Prüfungsbehörden vorgelegen hat.
Weiter erkläre ich, dass ich mich an keiner anderen Hochschule um einen Doktorgrad beworben habe.
Göttingen, den ...
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(Unterschrift)
2. Hiermit erkläre ich eidesstattlich, dass diese Dissertation selbständig und ohne unerlaubte Hilfe angefertigt wurde.
Göttingen, den ...
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(Unterschrift)