How do long-term land uses affect the organic carbon contents associated with aggregate fractions in an alluvial plain?

Abstract Due to the negative impacts of climate change, soil degradation and losses of soil organic carbon (SOC) in arable agricultural ecosystems are gradually increasing worldwide. Therefore, implementing agricultural management practices that increase organic carbon (OC) sequestration in soils with intensive agricultural production is essential for maintaining soil quality (SQ) and enhancing sustainable crop production. Understanding the effects of management practices on SOC stability requires understanding the resulting changes in the SOC fractions (labile or recalcitrant), the OC contents associated with aggregates, and the soil organic carbon stocks (SOC Stocks ). In the present study, soil samples were collected from three different depths in the Çarşamba Alluvial Delta Plain, located in Turkey’s semi-humid climate zone, to investigate the long-term effects (>5 years) of six different land use types (LUTs). Our results regarding average values revealed that the labile soil organic carbon (SOC LC ) and recalcitrant soil organic carbon (SOC RC ) fractions, OC contents associated with aggregates, and SOC Stocks changed significantly (p<0.01) in response to the effects of different LUTs. Compared to pasture land use, the contents of SOC LC and SOC RC were statistically decreased from 5.98 g/kg to 3.16 g/kg and from 6.37 g/kg to 3.43 g/kg (p<0.01), respectively, in soils under soybean land use. Also, it was found that both SOC fractions reduced statistically (p<0.01) with increasing soil depth. This study, which evaluated the long-term effects of different LUTs on SOC, revealed that SOC LC and SOC RC fractions can be successful indicators in assessing the effects of different LUTs and soil depths.