Soil‐derived trace gas fluxes from different energy crops – results from a field experiment in Southwest Germany

Willow coppice, energy maize and M iscanthus were evaluated regarding their soil‐derived trace gas emission potential involving a nonfertilized and a crop‐adapted slow‐release nitrogen (N) fertilizer scheme. The N application rate was 80 kg N ha −1 yr −1 for the perennial crops and 240 kg N ha −1 yr −1 for the annual maize. A replicated field experiment was conducted with 1‐year measurements of soil fluxes of CH 4 , CO 2 and N 2 O in weekly intervals using static chambers. The measurements revealed a clear seasonal trend in soil CO 2 emissions, with highest emissions being found for the N‐fertilized M iscanthus plots (annual mean: 50 mg C m − ² h −1 ). Significant differences between the cropping systems were found in soil N 2 O emissions due to their dependency on amount and timing of N fertilization. N‐fertilized maize plots had highest N 2 O emissions by far, which accumulated to 3.6 kg N 2 O ha −1 yr −1 . The contribution of CH 4 fluxes to the total soil greenhouse gas subsumption was very small compared with N 2 O and CO 2 . CH 4 fluxes were mostly negative indicating that the investigated soils mainly acted as weak sinks for atmospheric CH 4 . To identify the system providing the best ratio of yield to soil N 2 O emissions, a subsumption relative to biomass yields was calculated. N‐fertilized maize caused the highest soil N 2 O emissions relative to dry matter yields. Moreover, unfertilized maize had higher relative soil N 2 O emissions than unfertilized M iscanthus and willow. These results favour perennial crops for bioenergy production, as they are able to provide high yields with low N 2 O emissions in the field.