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SOIL & WATER MANAGEMENT & CONSERVATION

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

^a Departamento de Suelo y Agua, Estación Experimental de Aula Dei, Consejo Superior de Investigaciones Científicas (CSIC), POB 202, 50080-Zaragoza, Spain
^b Present address: Natural Resource Ecology Lab., Colorado State Univ., Fort Collins, CO 80523
^c Departament de Producció Vegetal i Ciencia Forestal, Universitat de Lleida–IRTA, Rovira Roure 177 25198 Lleida, Spain
^d Dep. of Soil and Crop Science, Colorado State Univ., Fort Collins, CO 80523
^e Lab. of Applied Physical Chemistry, Ghent Univ., Ghent, Belgium
^f Dep. of Geological Sciences, Univ. of Colorado, Boulder, CO 80309

^* Corresponding author (jalvaro.fuentes{at}gmail.com).

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 Peñaflor site, PN-BF and continuous barley at the Peñaflor 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 µm) was found under NT than under CT in the 0- to 5-cm depth. Macroaggregate organic C concentration (250–2000 µm) was greater in NT compared with CT in the BB cropping system, but did not differ with tillage treatment in the PN-BF rotation. Greater proportion of microaggregates within macroaggregates in 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.

Abbreviations: AG, Agramunt site • CT, conventional tillage • IC, inorganic carbon • iPOM, particulate organic matter occurring within aggregates • LF, light fraction • mSOC, mineral associated soil organic carbon • NT, no-tillage • PN, Peñaflor site • PN-BB continuous barley at Peñaflor site • PN-BF, barley-fallow rotation at Peñaflor site • POM, particulate organic matter • RT, reduced tillage • SOC, soil organic carbon • SOM, soil organic matter • SV, Selvanera site • Total mM-C, total microaggregate-associated carbon