During her PhD studies, Azhar Zhartybayeva worked with long-term field experiments to quantify carbon inputs and soil organic carbon (SOC) turnover in agricultural soils cropped with silage maize. Changes in SOC stocks are primarily driven by C inputs from crops and other organic amendments. However, key uncertainties remain in estimating the C in above- and belowground harvest residues and in determining how C inputs contribute to different SOC pools over time.

Azhar combined field-based measurements of above- and belowground maize residue with yield-based allometric functions used in SOC simulation models, natural-abundance δ13C to assess whether nutrient-induced differences in harvest yield lead to differences in harvest-residue C inputs, and to quantify the contribution of maize-derived C to SOC pools.

The findings improve understanding of how silage maize cropping influences SOC turnover in long-term field experiments under contrasting nutrient regimes and provide an empirical basis for improving model representations of crop-derived C inputs and SOC pool dynamics.

Time: 22/04/2026 at 12 : 00 
Place: 8814-3075, Auditorium, AU Viborg, Aarhus University, Blichers Alle 20, 8830 Tjele 
Title of PhD thesis: Carbon inputs and turnover in soil cropped with maize 
Contact information: Azhar Zhartybayeva, e-mail: azhara@agro.au.dk, tel.: +45 9193 7473
Members of the assessment committee:
Professor Claire Chenu Université Paris-Saclay, INRAE, AgroParisTech, UMR ECOSYS, France
Senior Scientist Christopher Poeplau, Thünen Institute of Climate-Smart Agriculture, Germany
Senior Researcher Henrik Skovgård (chair), Department of Agroecology, Aarhus University, Denmark
Main Supervisor:
Professor Jørgen Eriksen, Department of Agroecology, Aarhus University, Denmark
Co-supervisors:
Assistant Professor Johannes Lund Jensen, Department of Agroecology, Aarhus University, Denmark
Language: The PhD dissertation will be defended in English.