Vertical carbon and biochar transport in a sandy soil lysimeter experiment

Sandy soils are characterized by high water infiltration, low water and nutrient retention, and low soil organic matter (SOM). Organic soil amendments (OSA) can improve hydraulic properties and SOM levels, making them suitable for sustainable agricultural use. Additionally, biochar amendments sequester atmospheric carbon dioxide and interact with SOM, potentially enhancing its stability. This study analyzed carbon dynamics in a sandy soil following the addition of OSA, including dredged sediment (20 %) and compost (5 %), mixed with and without biochar (1 %). For this purpose, a lysimeter experiment was setup in Novi Sad, Serbia, and conducted for 441 days. Total organic carbon (TOC) stocks in the lysimeters were measured after the experiment and compared with the amounts of TOC added at the beginning. Drained water amounts were collected throughout the experiment and analyzed for truly dissolved organic carbon (DOC) and particulate organic carbon (POC) in the first six months. Black carbon was used to specifically analyze biochar in 5 cm increments of the lysimeter columns at the end of the experiment. This molecular marker revealed no significant vertical biochar transport but accumulation trends in intermediate lysimeter levels. The addition of compost exhibited the highest relative TOC loss with 24.5 %, although differences were not statistically significant. DOC leaching with increased by 0.17 % (p < 0.05) if compost was added purely. Mixing compost with biochar did not affect the TOC loss but significantly reduced DOC leaching. Sediment additions led to the highest relative POC loss with 0.023 % but were significantly mitigated (p < 0.05) by co-additions of biochar. Combining both OSA with biochar was associated with lower DOC and POC leaching than adding sediment and compost alone, while the relative TOC loss was not significantly affected. These findings suggest that biochar influences the partitioning and leaching of organic carbon in coarse-textured soil agroecosystems.