Enhancing soil C sequestration through organic matter recycling: A comparative study of paddy and upland fields

Winter cover crops are expected to increase soil organic C (SOC) stocks, but the magnitude of SOC gain could be greater in paddy fields where decomposition is constrained by anaerobic soil conditions, compared to upland fields. This study examines the impact of winter cover crop recycling on SOC accumulation over two years in South Korea. Plots were established in a rice paddy field and a nearby upland maize field, and each field was fertilized with organic or chemical inputs. In chemical treatments, where no cultivation occurred during winter, synthetic fertilizers (NPK) were applied at recommended doses for rice and maize. In organic treatments, barley and hairy vetch were grown during the winter fallow season and terminated by incorporation as organic amendments in the warm cropping season, prior to planting the annual rice or maize crop. Compared with chemical treatments, no significant effect of organic treatments on grain productivity was observed. However, organic treatments increased net primary production (NPP) by 46–81 %, regardless of field conditions. The higher C inputs with organic amendments were accompanied by greater C respiration—63–73 % more in paddy fields and 15–39 % higher in upland fields—than with synthetic fertilizer. Net ecosystem carbon balance (NECB) increased by 343–347 % in paddy fields and 15–39 % in upland fields under organic amendments. Consequently, rice paddy fields with organic amendments had an annual C accumulation of 1773–2168 kg C ha⁻¹. Conversely, despite extensive recycling of winter cover crops, maize cultivated in upland fields still experienced an annual net C loss of 4663–7789 kg C ha⁻¹. Recycling organic residues as a C source in rice paddy fields promotes SOC stock accumulation in temperate regions. Conversely, in maize upland fields, where organic plant recycling alone is insufficient for C sequestration, incorporating additional biomass, such as maize stover, is essential to offset the net SOC loss.