Soil Aggregation and Soil Organic Carbon Stabilization: Effects of Management in Semiarid Mediterranean Agroecosystems

In semiarid agroecosystems of the Ebro valley (NE Spain) soils are characterized by low soil organic matter (SOM) and a weak structure. In this Study we investigated the individual and combined effect of tillage system (no-tillage, NT; reduced tillage, RT; conventional tillage, CT) and cropping system (barley-fallow rotation at the Penaflor site, PN-BF and continuous barley at the Penaflor site, PN-BB) on soil organic carbon (SOC) storage as well as the physical protection of SOM fractions by soil aggregates in three long-term experimental sites. In both cropping systems, total SOC content was more than 30% higher in NT compared with CT in the 0- to 5-cm depth. The suppression of fallowing in the PN-BB cropping system led to a greater SOC stabilization only in NT In all the three sites, greater proportion of water-stable macroaggregates (>250 mu m) was found under NT than under CT in the 0- to 5-cm depth. Macroaggregate organic C concentration (250-2000 mu m) was greater in NT compared with CT in the 1313 cropping system, but did not differ with tillage treatment in the PN-BF rotation. Greater proportion of microaggregates within macroaggregates ill NT compared with CT was only found in the Agramunt site (AG). However, greater C stabilized inside these microaggregates was observed in AG, Selvanera site (SV), and PN-BB in the 0- to 5-cm depth. The results of this study demonstrate that in the semiarid Mediterranean agroecosystems of the Ebro valley, the adoption of NT together with the suppression of long-fallowing period can significantly increase the amount of SOC stabilized in the soil surface and improve soil structure and aggregation.