Long-term Impacts of Tillage and Cover Cropping on Soil Organic Carbon and Carbon Oxidizable Fractions in a Tropical Sandy Soil

A growing body of evidence has pointed out diverse factors limiting carbon (C) sequestration in soils under conservation tillage. This suggests the need for site-specific evaluations for better understanding agricultural practice effects and deployment of sustainable agriculture.

We used a long-term experiment (18 years) to explore 12 scenarios of corn production [conventional (CT), minimum (MT), and no-tillage (NT) combined with four cover crops] in a tropical sandy soil. The soil organic carbon (SOC), nitrogen (N) and C-pools with different turnover rates (active and passive) were measured over 60 cm depth. C-pools were determined under a gradient of C-oxidation.

Increments in SOC stocks in MT and NT were observed up to 40 cm depth, but it relied upon the cover crop choice. NT resulted in higher increments in the active-C pool (23%), while MT increased both the active (26%) and passive-C pools (78%) at 0–40 cm depth compared to CT. Higher N stocks were observed in conservation tillage systems than CT. Cover cropping did not influence SOC pools in superficial layers of CT. Conversely, it dictated the maximum C accrual over the soil profile (60 cm) of MT (53.9 Mg C ha^− 1) and NT (47.8 Mg C ha^− 1) systems. The combination of MT and leguminous species resulted in increments of up to 6 Mg C ha^− 1 in the active and passive-C pools when compared to CT.

Our study demonstrates that higher soil C and N storage downward tropical sandy soils profile can be achieved by a long-term combination of reduced soil disturbance and cover crop choice. MT has the ability to increase both labile-C and stable-C pools, thereby potentially promoting biological activity and acting as a longer-term C sink simultaneously.