Cup plant outperforms silage maize as a sustainable bioenergy crop

The cup plant (Silphium perfoliatum) offers an ecologically advantageous alternative to silage maize for bioenergy production. This is the conclusion of a multi-year comparative study conducted by researchers at the University of Bayreuth. Their findings have now been published in the journal GCB Bioenergy.

The search for sustainable alternatives to energy production from agricultural crops is a key concern in light of the European climate goals to achieve climate neutrality by 2050. In Germany, maize currently dominates as an energy crop, but its cultivation poses ecological challenges: soil erosion, nutrient leaching, and especially nitrate contamination of groundwater are well-known issues.

For this reason, research must identify suitable alternative crops that can minimize these environmental problems while maintaining similar levels of biomass production and energy yield.

The cup plant, a perennial species native to North America, is characterized by a deep-reaching root system and long-term usability. It is cultivated as an alternative to maize for energy production. Researchers from the Agroecology research group and the Botanical Garden (ÖBG) at the University of Bayreuth studied its growth and ecological potential over a four-year period using the lysimeter facility at the ÖBG—a system that allows for sampling of leachate.

This enabled the plants to grow under controlled conditions, both with adequate water supply and under moderate drought stress, simulating the challenges of climate change.

"Our findings clearly show that from the second year onwards, the cup plant produces more biomass than maize. Particularly noteworthy is the cup plant's ability to efficiently absorb nitrogen from the soil, drastically reducing nitrate—a nitrogen compound—leaching into groundwater," says Anna Hollweg, master's student in the University of Bayreuth's Agroecology research group and lead author of the study. In the third and fourth years of the experiment, nitrate leaching under the cup plant was up to 99% lower than under maize.

Even under moderate drought conditions, the cup plant remained comparatively stable. While maize produced less biomass under drought stress, the cup plant showed only minor losses. "In general, the cup plant's deep root system enables it to access water and nutrients in deeper soil layers. It also promotes the activity of soil microorganisms, which contributes to long-term improvement of soil quality," says Prof Dr. Johanna Pausch, Professor of Agroecology at the University of Bayreuth.

Thus, the cup plant not only represents an ecologically beneficial alternative to maize, but also proves to be a reliable energy crop under climate change conditions such as increasing drought.

"We propose a combination of maize and the cup plant during the establishment phase in the field to harness the advantages of both crops. Overall, the cup plant offers a promising perspective for agriculture that combines productivity with environmental protection," says Hollweg.