Completed doctorates

Two IGZ employees successfully defend their dissertations

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Anton Gasser (left, photo: private) and Eric Bönecke (right, photo: IGZ/E. Piontek) successfully defended their dissertations in April and May.
Anton Gasser (left, photo: private) and Eric Bönecke (right, photo: IGZ/E. Piontek) successfully defended their dissertations in April and May.

In April and May, the two IGZ employees Anton Gasser and Eric Bönecke successfully completed their doctorates at the Martin Luther University of Halle-Wittenberg. Both conducted the work on their PhD in the IGZ-Programme Area "Next-Generation Horticultural Systems" in the Research Group “Open Field Horticultural Systems”.

Anton Gasser's work was part of the FNR-funded "HUMOR" project and focused on assessing the quality of organic residues in terms of their carbon, nitrogen and phosphorus dynamics in agricultural soils. The dissertation was mainly carried out at the Helmholtz Centre for Environmental Research (UFZ) in Halle under the supervision of Dr Uwe Franko and Prof. Dr Martin Volk.

In the first part of his work, Anton Gasser focused on the evaluation of organic residues. The quality assessment was based on the mineralization dynamics of incubation experiments in which the carbon dioxide release was measured over a certain time period. Anton Gasser used mechanistic carbon landscape models to capture these turnover processes. A quality parameter (EHUM) was derived from the distribution of carbon in the various pools, which provides information on the contribution of an organic residue to the formation of humus. A value of one stands for a high humus formation efficiency and zero for no contribution of the analyzed residues to the humus formation, whereby this is independent of the incubation time.

Anton Gasser was then able to show that the parameters obtained from the incubation experiments, which describe the turnover dynamics of various organic and plant residues, are also suitable for modelling the carbon and nitrogen turnover of the same substances. The parameterization of the organic residues in the incubation trials means that no further optimization or parameterization is required for modelling their turnover under field conditions.

Finally, the environmental scientist focused on the phosphorus dynamics on agricultural soils. To this end, he extended the carbon turnover model CCB to include a phosphorus module that can model the dynamics of plant-available and total P. In addition to the organic phosphorus pool, the new CNP model also takes into account two mineral phosphorus pools, which are in a dynamic equilibrium with each other. The model was tested on four continuous field trials, and consistently good results were achieved with relative mean square deviation of less than 10% for plant-available phosphorus across all continuous field trials.

The results were published in peer-reviewed scientific journals.

Field trial in Thyrow (Brandenburg). Photo: J. Spiesecke.

In his cumulative doctoral thesis, Eric Bönecke dealt with the causes of temporal and spatial fluctuations in wheat yields and how these can be visualized using various methods on different temporal and spatial scales. The geographer also demonstrated a solution for managing soil-related heterogeneity in an environmentally friendly way.

In the first part of the thesis, he used mixed-effect models and data from a metadata collection to analyses the effects of climate change and weather extremes over the last six decades on yield variation and the yield level of winter wheat at various locations and regions in Germany. For the first time, the coefficient of determination for mixed-effect models, which was developed during the project time, was used to separately evaluate the magnitude of the various influencing environmental and agronomic factors on wheat growth. The work was carried out as part of a DFG-funded project at the Leibniz University of Hanover under the direction of Prof. Dr Hartmut Stützel.

In the second part of the work proximal-soil data from the Geophilus sensor platform was inverted for the first time in order to create soil texture maps from field samples and make them usable for process-oriented agricultural modelling at the field scale. The combination of methods was tested on a chernozem soil site and showed the strongest influence of small-scale soil variability on winter wheat yields, particularly through water availability in the subsoil in a relatively dry year. This part of the work was carried out as part of a BLE-funded project and was mainly supervised by Dr Uwe Franko at the Helmholtz Centre for Environmental Research in Halle.

In the final part of his doctoral thesis, he then proposed a solution as to how proximal soil sensors can improve the data basis for a site-differentiated fertilization strategy. For the first time, the work also used the stepless approach developed at IGZ to calculate fertilizer requirements. The example of liming clearly demonstrated that this precise farming method has significant advantages compared to conventional field-uniform management approaches. This part of the thesis was executed within the EU-funded project (EIP-Agri) "pH-BB - Precise Liming in Brandenburg" –  a joint project of the Eberswalde University of Sustainable Development (HNE), the Leibniz-Institute of Agrotechnology and Bioeconomy (ATB) and IGZ – which was lately awarded with the EIP-AGRI Innovation Prize in the category of Digitalization.

The doctoral thesis resulted in three peer-reviewed scientific articles published in high-ranked journals. The dissertation was reviewed by Prof. Dr Hans-Jörg Vogel from the Helmholtz Centre for Environmental Research (UFZ) and Martin Luther University Halle-Wittenberg and Prof. Dr Dr Kurt-Christian Kersebaum from the University of Göttingen and Leibniz Centre for Agricultural Landscape Research (ZALF).

We congratulate Dr Anton Gasser and Dr Eric Bönecke on completing their doctorates and wish them all the best for their future careers!

Publications of A. Gasser’s and E. Bönecke’s cumulative dissertations:

  • Gasser, A. A., Diel, J., Nielsen, K., Mewes, P., Engels, C., & Franko, U. (2022). A model ensemble approach to determine the humus building efficiency of organic amendments in incubation experiments. Soil Use and Management, 38(1), 179-190.
  • Gasser, S. A. A., Nielsen, K., & Franko, U. (2023). Transfer of carbon incubation parameters to model the SOC and SON dynamics of a field trial with energy crops applying digestates as organic fertilizers. Soil Use and Management, 39(1), 342-356.
  • Gasser, S. A. A., Nielsen, K., Eichler‐Löbermann, B., Armbruster, M., Merbach, I., & Franko, U. (2023). Simulating the soil phosphorus dynamics of four long‐term field experiments with a novel phosphorus model. Soil Use and Management, 39(2), 867-880.
  • Bönecke, E., Breitsameter, L., Brüggemann, N., Chen, T.W., Feike, T., Kage, H., Kersebaum, K.C., Piepho, H.P. and Stützel, H., 2020. Decoupling of impact factors reveals the response of German winter wheat yields to climatic changes. Global Change Biology, 26(6), pp.3601-3626.
  • Boenecke, E., Lueck, E., Ruehlmann, J., Gruendling, R. and Franko, U., 2018. Determining the within-field yield variability from seasonally changing soil conditions. Precision Agriculture, 19(4), pp.750-769.
  • Bönecke, E., Meyer, S., Vogel, S., Schröter, I., Gebbers, R., Kling, C., Kramer, E., Lück, K., Nagel, A., Philipp, G. and Gerlach, F., Palme, S., Scheibe, D., Zieger, K., Rühlmann, J., 2021. Guidelines for precise lime management based on high-resolution soil pH, texture and SOM maps generated from proximal soil sensing data. Precision Agriculture, 22(2).