Carbon saturation and translocation in a no-till soil under organic amendments

Studies suggest that intensively tilled soils have lost 25-75% of their original soil organic C (SOC) content. No tillage (NT) can restore SOC in response to increased C inputs and reduced soil disturbance. Organic amendments provide faster recovery of SOC, ultimately promoting the saturation of soil layers. Here we present evidence of additional SOC accrual through translocation of SOC after saturation of the topsoil layer in a NT soil. Both processes were observed in a long-term (25 yr.) experiment comparing soil tillage systems (chisel tillage − CT, and NT) in central Kansas. Plots with continuous corn were amended with mineral (MF) and organic N (OF), in addition to a control treatment without N fertilization (CO). Accumulation of SOC was limited to the surface layer (0-5 cm) of the NT soil amended with MF. Organic fertilization increased SOC in the 0-5 cm soil layer from 9.5 Mg C ha−1 to a level of 16.2 and 30.2 Mg C ha−1 in CT and NT, respectively. Further analysis confirmed the saturation of physically protected SOC in the surface of NT soil under organic amendments. After saturation, significant SOC accrual (1.3 Mg C ha−1 yr−1) was observed in the 5-15 cm soil layer. Isotopic assessment confirmed the occurrence of SOC translocation between saturated and C-depleted NT soil layers. No evidence of SOC translocation was observed between non-saturated soil layers. Further research is needed to elucidate the mechanisms regulating this process. Nonetheless, SOC translocation and subsequent SOC accrual suggests a greater C sink potential for NT soils than previously thought.