Long-term impact of farming systems on soil organic carbon restoration in sandy soil in the southeastern US

Implementing optimal management practices is crucial for restoring soil organic carbon (SOC), mitigating climate change, conserving resources, and preserving biodiversity. This study evaluated the long-term (~23 years) impact of diverse farming practices on soil organic matter (SOM) fractions in sandy coastal soil in the southeastern United States. The treatments included conventional tillage, no-till with winter cover crops, organic systems with intense or reduced tillage, integrated crop-livestock systems, and agricultural abandonment. Results showed that the organic carbon (OC) and nitrogen (N) content (g kg−1 fraction) in the mineral-associated organic matter (MAOM) and coarse particulate organic matter (cPOM) were highest (P < 0.05) in the organic systems compared to the conventional systems. The correlation between SOC and the OC and N in the different fraction content was significant (r=0.5-0.9, P < 0.001). The ninhydrin reactive-N in the conventionally tilled system was 70-160% higher (P < 0.05) than in other systems. Our results indicate that leguminous cover crops and organic fertilizers were crucial for POM-OC restoration. In addition, organic treatments increased the OC and N content of MAOM without changing the mass concentration of MAOM, suggesting an influence on MAOM composition but not the total quantity of MAOM in the soil. The study highlights the significance of the quality of N inputs due to diverse management systems on SOC restoration.