Potential C-storage in soils when cultivating the perennial cup plant (Silphium perfoliatum L.) – a field trial study in western Germany

In contrast to other energy crops, cup plant features numerous ecological benefits. Based on the ecophysiology of the cup plant as a perennial and deep rooting crop, a significant potential for soil organic carbon (SOC) accumulation can be assumed. However, such data under practice farming conditions are missing up to now.

A field study was performed on 17 newly established cup plant sites on arable farm land in 2018. They were located in a low mountain range in Western Germany and managed by the respective farmers. Shortly after establishment, soil organic carbon stocks in topsoil and subsoil down to 45 cm depth were determined and repeated five years later in 2023.

Predominantly, increases in SOC stocks could be observed. Annual accumulation rates ranged between 400 kg C ha⁻¹ yr⁻¹ and approx. 1500 kg C ha⁻¹ yr⁻¹. Significant accumulation of SOC was especially observed in the subsoils whereas several topsoils lost SOC. The losses in the topsoil may result from high tillage intensity for seedbed preparation for cup plant establishment in combination with the low aboveground biomass development in the first two years of cultivation resulting in low amounts of aboveground litter. Increases in subsoil SOC indicate for the higher translocation of assimilation products into the root system. Root exudation and root biomass turnover in combination with lower SOC turnover rates in the subsoil likely present the basement for intense SOC accumulation in subsoils under cup plant cultivation.

Our results reveal that the cultivation of cup plant may contribute to climate change mitigation and may further improve soil quality.