Soil organic carbon sequestration and tillage systems in the Mediterranean Basin: a data mining approach

This study has reviewed 66 long-term experimental comparisons on Soil Organic Carbon (SOC) and tillage systems in Mediterranean arable crops (from 15 sites located in Greece, Italy, Morocco and Spain), with the aim to identify the biophysical and agronomic variables most associated with C sequestration rate. Data were organized in a dataset containing basic environmental descriptors (elevation, temperature, rainfall), information on soil tillage system (conventional, minimum, no-tillage), soil attributes (pH, particle size distribution and texture), crop rotation, fertilization, time length of the experiment, initial and final SOC stocks. The collected information were analyzed using a data mining approach including Spearman non-parametric correlations, Principal Component Analysis (PCA), hierarchical clustering and step-wise multiple regression. Tillage, crop rotation, and fertilization were the most significant factors affecting C sequestration rate. Non-parametric correlations reported negative coefficients for initial SOC stock, length of the experiment, mineral fertilization, tillage and production system. C sequestration rate increased significantly under no-tillage. Hierarchical clustering indicates that geographical proximity reflects similarity in biophysical conditions and agronomic practices. PCA outlined a positive correlation of SOC with soil depth, elevation and sites located in Spain and a negative correlation with mean air temperature, mineral fertilization, irrigation, experiment's length and sites located in Greece. C sequestration rate was positively associated with mean air temperature. Finally, a step-wise multiple regression indicated that C sequestration rate increased in sites exposed to colder climate conditions and under no-tillage.