2.3. Incubation experiment
A short-term aerobic incubation procedure was used to determine the potential of the soil samples to mineralize organic C. Soils sampled at the end of the trial (February) from the upper, middle, lower trams of the plot C4-SOC strip and the Control site (soil neighbor to the plot) were used for the incubation experiment. Soil samples (10 g) at 50% of their water holding capacity were pre-incubated for five days at room temperature; then, after readjustment of the moisture, they were incubated at 25 °C in 125 cm3 air-tight glass bottles. CO2 measurements were done after 1, 3 and 7 days from the start. Twenty-four hours before the CO2 sampling, all flasks were ventilated for 30 min with fresh room air and then immediately sealed with rubber stoppers. Thus, evolved CO2 from soil was allowed to accumulate for 24 h and then sampled. To correct the dilution by atmospheric CO2 in the incubation glass bottles, for each sampling date, the CO2 concentration and isotopic