Carbon storage in agricultural topsoils and subsoils is promoted by including temporary grasslands into the crop rotation

Authors: GUILLAUME, THOMAS - AGROSCOPE; MAKOWSKI, DAVID - INRAE; Libohova, Zamir; ELFOUKI, SAID - AGROSCOPE; FONTANA, MARIO - AGROSCOPE; LEIFELD, JENS - AGROSCOPE; BRAGAZZA, LUCA - AGROSCOPE; SINAJ, SOKRAT - AGROSCOPE

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2022
Publication Date: 5/9/2022
Citation: Guillaume, T., Makowski, D., Libohova, Z., Elfouki, S., Fontana, M., Leifeld, J., Bragazza, L., Sinaj, S. 2022. Carbon storage in agricultural topsoils and subsoils is promoted by including temporary grasslands into the crop rotation. Geoderma. https://doi.org/10.1016/j.geoderma.2022.115937.
DOI: https://doi.org/10.1016/j.geoderma.2022.115937

Interpretive Summary: Agricultural soils are considered as one of the major sources for sequestration of the atmospheric C. Converting agricultural land to permanent grasslands has the highest potential for increasing the amount of C stored in the soil. However, such scenario is unrealistic given the increased pressure on existing agricultural land to support growing demand for food. This study found that incorporating temporary grassland in rotations in agricultural systems in modest amounts (10%) would increase the soil organic carbon in soil. In addition, significant amounts of C will be stored in the subsoil (20-50cm), which would also contribute to the stability of C in agricultural systems.

Technical Abstract: Atmospheric C sequestration in agricultural soils is viewed as one of the most promising negative emission technologies currently available. Nonetheless, the soil organic carbon (SOC) storage potential in cropland soils remains highly uncertain. In particular, it remains unclear how strongly subsoil SOC stocks respond to agricultural practices. Here, we assess the SOC storage potential in croplands and how the presence of temporary grasslands (TG) in the crop rotation affects SOC stocks. We developed a new approach to correct for bias in bulk density (BD) induced by stone, sampling conditions and land-use effects using a data-driven model to predict the BD of fine soil (< 2 mm) for reference condition. Using 54 permanent grassland and cropland sites with various proportion of TG from a monitoring network in Switzerland, we showed that SOC stocks differences down to 50 cm depth between cropland and permanent grasslands (maximum: 2.96 ± 0.77 kg C m-2) depended on the TG proportion in the crop rotation regardless of clay content and pH. An increase of the TG proportion by 10 % would induce a SOC gain of 0.395 ± 0.130 kg C m-2. The responses of topsoil (0-20 cm) and subsoil (20-50 cm) SOC stocks to TG proportion were linear and equivalent. The effect of TG on SOC storage would have been underestimated by 58% without including subsoil and by 15 % without BD corrections. The conversion of all croplands to permanent grasslands in the study region would potentially store SOC that is equivalent with the total greenhouse gas emissions generated by the same region during one year. Although the potential of agricultural soils as negative emission technology is relatively modest compared to former expectations, the findings demonstrate the potential to manage SOC and its associated ecosystem services at large scales and in deep soil layers.