Irrigation and SOC sequestration in the region of Navarre in Spain

The project REGADIOX, funded by the European Commission LIFE Program was based on the establishment of a regional-scale network of representative agricultural plots in three irrigation districts in Navarre (NE Spain). The project allowed for a rational evaluation of soil organic C (SOC) sequestration and greenhouse gases (GHG) emissions balances by using paired comparisons in terms of soil characteristics in irrigated vs rainfed plots. The results showed a clear influence of irrigation in soil condition, arising from greater SOC storage. The net effect was however modulated by soil characteristics and management practices, in so far as the different agricultural strategies did have different potential to sequester SOC and/or reduce GHG emissions. While permanent crops with green cover (which was possible thanks to irrigation) or semi-permanent crops as alfalfa were win-win strategies with positive C balances, intensive systems with two crops per year, although they also contributed to SOC gains, represented increased GHG emissions. The observed changes in SOC associated to irrigation with different managements also showed that irrigation adoption can alter the soils’ capacity to provide key ecosystem services beyond biomass production, as changes in soils properties related to SOC, such as water-holding capacity or soil erodibility were also observed. These changes were, however, not straightforward and varied depending on soil type, climate and time under irrigation