Marianna Deppe

How does reduced summer precipitation affect greenhouse gas emission from agricultural soils? Can nitrous oxide (N₂O) emissions from agriculture be reduced by placed N fertilization? These questions were addressed by Marianna Deppe during her dissertation project at the Thünen-Institute for Climate-Smart-Agriculture.

In collaboration with the Thünen-Institut for Biodiversity, the first project dealt with the effect of induced summer drought on fluxes of methane (CH₄) and N₂O, both potent greenhouse gases, between soil and atmosphere in sorghum and maize stands. Reverse effect were found: While CH₄ uptake in soil increased during drought phases, N₂O emissions slightly increased in winter. These results may help to predict feedback effects of greenhouse gas emissions.

In collaboration with the Julius-Kühn Institute of Soil Science and Plant Nutrition, a second project dealt with N₂O formation in soil in and around ammonium (NH4+) depots of the so-called CULTAN (Controlled-uptake-longterm-ammonium-nutrition) fertilization. Field experiments with summer wheat at sandy loam and loam sites did not confirm the expected decrease in N₂O emission. ¹⁵N isotope tracer experiments showed that (1) the formation of nitrate from ammonium fertilizer was not effectively inhibited and (2) only a small part of the N₂O emitted stemmed from the applied fertilizer. Increased yields with CULTAN fertilization show the potential for reduced N fertilization and thus imply an indirect mitigation potential for greenhouse gas emissions.