Tillage and cropping effects on soil organic carbon in Mediterranean semiarid agroecosystems: Testing the Century model

Carbon sequestration in agricultural soils can contribute to offsetting CO2 anthropogenic emissions and also to enhance soil fertility, soil water retention and crop production. In this experiment, our main objective was to validate the Century model for Mediterranean semiarid agroecosystems and to investigate management effects on soil organic carbon (SOC) dynamics in these areas. Data from a long-term experiment in NE Spain comparing three tillage systems (no-tillage, NT; reduced tillage, RT; conventional tillage, CT) and two cropping systems (barley-fallow rotation, BF and continuous barley system, CB) was used to simulate SOC with the Century model in the 0–30 cm soil depth. The model was able to accurately simulate SOC and above-ground C inputs under different tillage systems although it over-estimated C inputs in some growing seasons (e.g. 2000). Simulated and measured C inputs showed a significant relationship (P < 0.001; R2 = 0.83) and both tended to decrease as tillage intensity decreases but differences were not statistically significant. However, SOC content was greater under NT than under CT and RT. Also, intensification of cropping systems (i.e. eliminating bare fallow) led to greater SOC in all tillage treatments. Consequently, SOC sequestration rates were greatest in NT followed by RT and CT in the CB system with 0.46, 0.24 and 0.18 Mg C ha−1 yr−1, respectively. In the BF rotation lower SOC sequestration rates were found with values ranged from 0.15 to −0.004 Mg C ha−1 yr−1 in NT and CT, respectively. Both simulation and measured values showed that reduction in tillage intensity and an intensification of the cropping system are promising strategies to increase SOC sequestration under semiarid Mediterranean conditions. The Century model is a useful tool to simulate tillage and cropping system effects on SOC dynamics in semiarid Mediterranean agroecosystems.