This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

No abstract

European policy recommends that biomass production occur on marginal land, such as poorly draining Stagnosols. Compared to annual cropping, perennial crops may better mitigate N2O emissions at such sites, through more complete denitrification. To test that hypothesis, we compared N2 and N2O fluxes from the soils of a perennial crop (cup plant, Silphium perfoliatum L.) and an annual crop (silage maize, Zea mays L.). Intact soil columns (35 cm height, 14.4 cm diameter) were incubated for 37 days. The soils were fertilized with 60 or 120 kg N ha−1 and exposed to successive phases of waterlogging: free drainage, waterlogging of 1/3-, and waterlogging of 2/3- of the column. Source-specific N2O and N2 fluxes were measured using the 15 N gas flux method. Denitrification was higher in cup plant than maize soil and total N losses from denitrification were dominated by emissions from the third phase. Cup plant soil emitted 33.6 ± 78.1 mg N m−2 and 95.8 ± 64.4 mg N m−2 more N2O than maize soil in the low and high N treatments, respectively. The product ratio of denitrification (N2Oi = N2O/(N2 + N2O)) increased with waterlogging in maize soil, while remaining stable in cup plant soil. Emissions from the top 10 cm dominated the N2Oi rather than N2 fluxes from the saturated soil. This study did not show N2O mitigation in cup plant soil, instead highlighting the complexity of plant-soil effects on denitrification. We clearly showed that the application of a general N2Oi for agricultural soils across annual and perennial cropping is not recommended.

<p>In the last two decades, acreage for biomass production has strongly increased in Germany due to the Renewable Energy Act. Recently, discussion about soil, climate, and biodiversity protection is receiving more and more public attention throughout broad parts of the society. The project BESTLAND focuses on the effect of land use change from the common annual maize cropping system to a perennial cropping system, as a measure against increasing environmental constraints in biomass production. A suitable perennial biomass crop as an alternative for maize is S. perfoliatum (cup plant). On one hand, the yellow flowering plant produces high biomass yields and on the other hand it provides a variety of ecosystems services. Field experiments were carried out in the Saar-Nahe mountain range in the state of Saarland on a fine textured planosol. The experimental sites are characterized by temporal waterlogging and slopes and therefore these sites are prone for soil compaction and soil erosion. Under these conditions perennial crops are assumed to have soil preserving benefits. Maize was compared to cup plant by establishing four paired sites, where each pair consisted of a maize and a cup plant field in close vicinity (< 500 meters) to each other. All sites are grower fields and were managed by the farmers according best management practices. Nitrous oxide and methane fluxes were measured weekly using the static chamber technique all year round. Besides greenhouse gas measurement, soil samples for determination of soil mineral nitrogen were taken at each gas sampling date. Furthermore, soil temperature and water content were continuously monitored using sensors. Biomass yields at each site were determined at harvest. In the first year average nitrous oxide emissions from cup plant fields were lower than from maize fields by more than 70 % on area and dry matter yield basis. These results indicate that perennial bioenergy crops not only offer a wider range of ecosystem services but can also decrease GHG emissions from bioenergy production.</p>

Background The sustainability of bioenergy is strongly affected by direct field‐derived greenhouse gas (GHG) emissions and indirect emissions form land‐use change. Marginal land in low mountain ranges is suitable for feedstock production due to small impact on indirect land‐use change. However, these sites are vulnerable to high N2O emissions because of their fine soil texture and hydrology. Aims The perennial cup plant (Silphium perfoliatum L.) might outperform silage maize (Zea mays L.) on cold, wet low mountain ranges sites regarding yield and ecosystem services. The aim of this study was to assess whether the cultivation of cup plant also provides GHG mitigation potential compared to the cultivation of maize. Methods A t‐year field experiment was conducted in a low mountain range region in western Germany to compare area and yield‐scaled GHG emissions from cup plant and maize fields. GHG emissions were quantified using the closed chamber method. Results Cup plant fields emitted an average of 3.6 ± 4.3 kg N2O‐N ha–1 year–1 (–85%) less than maize fields. This corresponded to 74.0 ± 94.1 g CO2‐eq kWh–1 (–78%) less emissions per produced electrical power. However, cup plant had a significantly lower productivity per hectare (–34%) and per unit of applied nitrogen (–32%) than maize. Conclusion Cup plant as a feedstock reduces direct field‐derived GHG emissions compared to maize but, due to lower yields cup plant, likely increases emissions associated with land‐use changes. Therefore, the increased sustainability of bioenergy from biogas by replacing maize with cup plant is heavily dependent on the performance of maize at these sites and on the ecosystem services of cup plant in addition to GHG savings.