Perennial Cup Plant (Silphium perfoliatum L.) Outperforms Silage Maize (Zea mays L.) in Root Biomass and Nitrate Retention

Achieving European climate neutrality by 2050 will require an increase in energy production from renewable sources. Silage maize (Zea mays L.), the most commonly used crop in Germany, is increasingly subject to yield losses associated with soil degradation and nutrient depletion. The perennial cup plant (Silphium perfoliatum L.) has emerged as an alternative to reduce nutrient losses, mainly nitrogen (N), while maintaining similar biomass production. A lysimeter experiment was conducted to evaluate N dynamics between plant, soil, and leaching for maize and cup plant under moderate drought and well-watered conditions over 4 years. After the first year of growth, cup plant had higher shoot and root biomass than maize regardless of the watering conditions (e.g., in 2021 mean shoot biomass of maize was 266 g m⁻¹ compared to 2696 g m⁻¹ of cup plant). Notably, moderate drought did not affect shoot biomass in either crop (except in 2021 and 2022 for the cup plant). The higher biomass production of the cup plant was associated with higher N concentration in the shoot tissue compared to maize, likely due to its more efficient soil N utilization. This result was further supported by the lower soil dissolved N concentration and a reduction of nitrate leaching of 88% in 2021 and by up to 99% in 2022 under cup plant compared to maize. A higher microbial biomass N under cup plant suggests enhanced N immobilization by microorganisms. This is further supported by a higher microbial C/N imbalance under cup plant than maize in 2022, indicating a stronger N relative to C limitation. Our results showed that cup plant can provide high shoot and root biomass and significantly reduced nitrate leaching, indicating its potential as an alternative to maize and thus as a bioenergy crop for environmental sustainability in a changing climate.