Björn Kemman

On June 29th, 2022, Björn Kemmann successfully defended his PhD thesis “Assessment of field-derived greenhouse gas mitigation potential in biomass production by replacing maize with cup plant (Silphium perfoliatum L.) in low mountain ranges” at the Faculty of Agricultural and Nutritional Sciences in the Department of Agronomy at the Christian Albrechts University in Kiel (Prof. Dr. Henning Kage). The dissertation was part of the joint project "BESTLAND", which dealt with the cultivation of cup plant on periodically waterlogged sites in low mountain ranges.

Together with the emissions from indirect land-use change (iLUC), direct field-derived greenhouse gas (GHG) emissions have a strong impact on the GHG balance of bioenergy. The competition of biomass production with food production for arable land is the cause of the so-called iLUC emissions. To mitigate iLUC emissions due to the competition for arable land, biomass production should be restricted to marginal sites. The low mountain ranges in Germany might represent such marginal land. However, silage maize does not exploit its full yield potential in the cold, wet climate of the low mountain ranges. Moreover, the cultivation of maize on slopes carries a high risk of soil erosion. The newly introduced cup plant (Silphium perfoliatum L.) with its winter hardiness and high water demand is particularly suitable for low mountain ranges and due to its persistent roots, cup plant might prevent soil erosion. Therefore, cup plant represents a more sustainable alternative to maize on marginally productive sites of low mountain ranges.

Whether cup plant also provides a GHG mitigation potential on these sites, which are prone for denitrification due to their hydrology, was the question of Björn Kemmann’s thesis.

In a two-year field experiment field GHG emission were measured in cup plant and maize fields. The GHG emissions were related to the energy yield of both crops. Parallel to the field experiment, two incubation experiments were conducted under controlled conditions in the microcosm facility of the Thünen Institute of Climate-Smart Agriculture in order to elucidate nitrogen cycling and denitrification in maize and cup plant soil on a process scale.

Under field conditions cup plant emitted significantly less N₂O than maize. However, the energy hectare yield of cup plant was around 30% lower than that of maize, which increases the risk of iLUC emissions. Therefore, the GHG mitigation potential is strongly dependent on the yield potential at the marginal site and the field-derived GHG emissions during cultivation. Under laboratory conditions, no N₂O mitigation was observed in cup plant compared to maize soil. Cup plant soil generally exhibited higher denitrification rates than maize soil, but also a more pronounced reduction of N₂O to N₂. Hence, the observed lower field emissions of cup plant than maize are most likely due to the lower nitrate levels in the soil and the increased reduction of N₂O to N₂.