Soil organic carbon saturation in cropland-grassland systems: storage potential and soil quality

Authors: GUILLAUME, THOMAS - Agroscope; MAKOWSKI, DAVID - Inrae; Libohova, Zamir; BRAGAZZA, LUCA - Agroscope; SALLAKU, FATBARDH - Agricultural University Of Tirana, Albania; SINAJ, SOKRAT - Agroscope

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2021
Publication Date: 10/18/2021
Citation: Guillaume, T., Makowski, D., Libohova, Z., Bragazza, L., Sallaku, F., Sinaj, S. 2021. Soil organic carbon saturation in cropland-grassland systems: storage potential and soil quality. Geoderma. 406. Article 115529. https://doi.org/10.1016/j.geoderma.2021.115529.
DOI: https://doi.org/10.1016/j.geoderma.2021.115529

Interpretive Summary: Reliable estimations of soil organic carbon (SOC) deficits in agroecosystems are crucial in evaluating the potential of agricultural soils to store carbon and support management decisions at the farm level. Adequate SOC levels can also improve soil health. In this study we assessed the potential of soils to store SOC and identify the properties that contribute to increasing the SOC storage capacity. The agriculture soils had less SOC stored than the grassland soils. This difference presents a potential for agroecosystems with crops and grassland in rotation to store more SOC. The increase of the proportion of grassland in relation to the crops in the farming systems was identified as one of the efficient ways to increase the SOC storage. Also, the maximum storage SOC capacity and stability was related to soil texture. Soils with finer texture (like clay and silty soils) have larger capacity to store SOC compared to coarser textured soils (sandy soils). This research shows that finer textured soils should be targeted for increasing carbon storage in soils. However, it takes longer for these finer texture soils to achieve the maximum storage SOC capacity compared to sandy soils, but on the other hand, the SOC is more stable in finer texture soils. Although grasslands may have more capacity to store SOC than what this study found, the current SOC represents a realistic benchmark for estimating the potential of agricultural soil to sequester atmospheric C and for setting management priorities for agricultural soils under farm management systems.

Technical Abstract: Here, we assessed SOC saturation and soil physical quality in permanent grasslands (PG) and croplands (CR) by applying the C-saturation concept and the SOC:clay ratio as an indicator of soil physical quality to a set of long-term monitoring sites in western Switzerland. For this goal, we produced a new relationship between the silt + clay (SC) particles and the C stored in the mineral-associated fraction (MAOMC) and we tested the assumption that grasslands can be used as carbon-saturated reference sites. The saturation in PG was not coincidental as it depended on the C accrual history. Hence, PG with the lowest MAOMC have not reached their C-saturation level and present a potential SOC storage under optimal management. The MAOMC saturation in CR was low (62 ± 4%) and corresponded to a deficit of - 8.8 ± 1.2 mg C g-1 soil as compared to the current level in PG. The saturation was mainly affected by the proportion of temporary grassland in the crop rotation. The relative distribution of C between MAOM (~80%) and the fine and coarse particulate organic matter (POM) was not affected by land-use types. The MAOMC saturation in this study (MAOMC = 0.372 x SC + 4.23) was similar to that reported by other studies, but discrepancies appeared when the silt and clay contents were considered separately. By contrast to other studies, the C content of MAOM in PG (up to 54 mg C g-1 SC) was not related to the SC content. The SOC:clay ratio was correlated with MAOMC saturation in CR but not in PG. This shows that targeting SOC accrual in CR optimizes benefits between soil C sequestration and soil quality.