Soil organic carbon stock on the Majorca Island: Temporal change in agricultural soil over the last 10 years

For quite a long time, soil organic carbon stock (SOCS) has reduced from reconverting forest areas into agricultural land or by inadequate agronomic practices. However in recent decades in Mediterranean areas, abandonment of agricultural areas due to lack of economic profits and to promoting tourism has fostered a change in land use that has impacted soil carbon. In line with this, the Majorca Island (Spain) could be a good study area to evaluate temporary changes in carbon stocks in soils in areas with a Mediterranean climate. The present study analysed the spatial distribution of SOCS and evaluated the temporal changes over 11 years in agricultural soils in relation to the influence of land use and land management'. The global carbon budget (estimated at 30 cm depth) on the Majorca Island was estimated at 31.23 Tg C, and showed wide spatial variability. As expected, SOCS was higher in the forest areas of the Tramuntana Mountain Range ( > 100 Mg ha(-1)), while the lowest contents were found in agricultural use (79.3 Mg ha(-1)), located mainly in the centre and south of this island. The total C stored from 2006 to 2017 increased by 2.62 Tg C (15%) in agricultural areas on the island. We noted a major increase in SOCS in the agricultural zones on mountain slopes ( > 2-fold higher), associated with abandoned crops in terrace cultivation, but grassland systems also increased. Nonetheless, the present study shows a sharp drop in SOCS in the centre and south of this island. This decrease was more pronounced in annual crops ( -14.5%), which could be attributed to intensive soil management and increased irrigated land. Land abandonment has been indicated as the main potential to carbon sequestration in soil, but this potential for carbon sequestration is a finite process. Certain changes in agricultural practices on Majorca, and in rural Mediterranean areas in general, are necessary to avoid carbon loss in cropland soils. Adoption of conservation agriculture practices, e.g. cover crops, crop rotation, organic additions and reduced tillage techniques, can help increase SOC levels in rural Mediterranean areas.