Soil carbon and nitrogen changes after 28 years of no-tillage management under Mediterranean conditions

• Continuous NT increased SOC and STN content in the 30 cm soil depth by 22%.
• Continuous CT decreased SOC and STN content by 3% and 5% in the same soil layer.
• 28-yr SOC accumulation under NT was negligible in deep soil layers (10–60 cm).
• Under NT mean annual C sequestration rate in the 0–30 cm soil layer was 0.40 Mg ha−1 yr−1.
• Under NT a new steady state of SOC was estimated to occur after 40–50 years.

Mouldboard ploughing is known to accelerate soil organic matter (SOM) mineralization rate in Mediterranean regions. Long-term reduced tillage intensity potentially diminishes soil organic carbon (SOC) and total nitrogen (STN) depletions. Here, we compared long-term no-tillage (NT) and conventional tillage (CT) impact on SOC and STN sequestration rates at different depths ranging from 0 to 30 cm. The long-term experiment started in 1986 on a Typic Xerofluvent soil in Central Italy using a randomized complete block design with four replications. Ten years after the experiment began, SOC and STN concentrations in the 0–30 cm soil layer were already higher under NT compared to CT. The shallow layer (0–10 cm) showed the highest SOC and STN concentration increments. However, no differences between tillage systems were observed in the deeper layers. After 28 years, continuous NT increased SOC and STN content in the 30 cm soil depth by 22% compared to initial values. In the same period, continuous CT decreased SOC and STN content by 3% and 5%, respectively. On average, the total SOC and STN gains under NT may be attributed to the shallow layer increments. In the 10–20 and 20–30 cm soil layers, SOC accumulation over time was negligible also under NT. In the whole profile (0–30 cm), the mean annual SOC variation was +0.40 Mg ha−1 yr−1 and −0.06 Mg ha−1 yr−1 under NT and CT, respectively. Under NT, SOC content increased rapidly in the first ten years (+0.75 Mg ha−1yr−1); later on, SOC increments were slower indicating the reaching of a new equilibrium. Data show that NT is a useful alternative management practice increasing carbon sequestration and soil health in Mediterranean conditions.