Have we reached the turning point? Looking for evidence of SOC increase under conservation agriculture and cover crop practices

Increasing soil organic carbon (SOC) stocks in agricultural soils is currently of special interest because it can help mitigate global warming through atmospheric carbon (C) sequestration. Recommended management practices, such as conservation agriculture (CA) and conventional tillage with cover crops (CC), could have significant implications for C sequestration potential. A field experiment was carried out in northeast Italy to compare the implementation of CA and CC with conventional agriculture (CV). The experiment began in 2010 on three farms to evaluate SOC stock variation over a 6-year period. Two extensive soil sampling operations were conducted in 2011 and 2017 in 240 locations, for a total of 1,440 analysed soil samples, considering the SOC stratification within a 0–50-cm profile. The results suggested that CA changed the SOC distribution rather than the total amount of SOC. Compared to CV, after the introduction of CA, a general increase in SOC (0.25 Mg C ha−1 y−1) was observed in the 0–30-cm layer, whereas no stock variation was observed in the 0–50-cm layer. In contrast, compared to CV, the use of CC decreased the SOC stocks by 0.74 Mg C ha−1 y−1 in the 0–50-cm layer. Over a 6-year period, no benefit in SOC sequestration was observed with CA and CC. However, we hypothesize that these findings could still be affected by transitory dynamics, highlighting the low soil reactivity to soil-improving agricultural systems. A longer study period would be required to better understand the potential benefits of CA and CC on SOC sequestration. Highlights: We hypothesized that conservation practices increase SOC after a 6-year adoption No-tillage enhanced SOC stratification in conservation agriculture C addition with cover crops induced SOC stock reductions due to a priming effect An SOC increase was not observed after 6 years of conservation practices.