The Contribution of the Management of Landscape Features to Soil Organic Carbon Turnover among Farmlands

Background: Landscape features (LF—i.e., the natural and semi-natural areas in agricultural landscapes) positively contribute to soil organic carbon (SOC) sequestration and storage among farmlands. LF-related SOC partitioning still needs context-specific investigation to properly address climate change mitigation goals. Not many studies address LF phytocoenoses traits relation with SOC partitioning. Our study investigates SOC partitioning (total organic carbon [TOC]; labile dissolved organic carbon [DOC]; stable recalcitrant organic carbon [ROC]) between arable fields (AGR) and semi-natural/natural components (NAT: herbaceous field margins, young/mature hedgerows, young/mature woods) in a temperate alluvial pedoclimatic context (Po Plain, Northwestern Italy). Methods: We compared topsoil SOC and its fractions (0–20 cm depth) between: AGR-NAT sites; hedgerows (HED)-AGR sites; and different ecological quality degrees (phytocoenoses were classified by Biological Territorial Capacity [BTC] values and Index of Vegetation Naturalness categories [IVN]--). Results: Our results confirmed a significantly different SOC partitioning behaviour between AGR and NAT sites (NAT: +79% TOC; +409% ROC); AGR sites were negatively correlated with ROC. TOC was a robust ROC predictor. HED had significantly higher TOC (+71%) and ROC (+395%) compared to arable fields, with the highest values in mature hedgerows. DOC showed contrasted behaviours. A linear regression model on BTC and IVN (predictors) and TOC and ROC showed significant positive relationships, especially for ROC. Conclusions: Our study confirmed the LF role in long-term SOC storage among farmlands, which should be coupled with AGR management (with prevalent short-term SOC fractions). LF ecological quality was a determining factor in total and long-term SOC. Proper LF management is pivotal to aligning climate change mitigation goals with other ecological benefits.