Due to particular soil and climate conditions and inappropriate agricultural practices, Aragon (NE Spain) is a
region prone to land degradation by water erosion. For this reason, the adoption of conservation tillage systems
has been encouraged as an alternative to preserve soil and water in this region. However, little information
concerning soils on which these techniques are applied is available. The main objectives of this study were to
assess the effect of long-term no tillage (NT) on water aggregate stability infive different cereal production
areas of Aragon and identify the main mechanisms involved on aggregate breakdown. The study was conducted
under on-farm conditions where pairs of adjacentfields under NT and conventional tillage (CT) were compared.
In all cases, a nearby undisturbed soil under native vegetation was included. Soils were slightly to highly calcareous with medium textures ranging from sandy loam to silty clay loam. Results indicate that NT increased surface
aggregate stability with respect to CT systems through lower soil disturbance and higher organic carbon (OC)
content at the soil surface (0–5 cm depth). Slaking was the dominant disaggregation process of the cultivated
soils, representing 40–80% of total soil disruption, and was strongly and negatively affected by aggregateassociated OC. This soil property together with the silt content (weak and positive effect) explained more than
80% of the slaking variation. Swelling and clay dispersion were less frequent processes and their occurrence
seemed to be associated with high silt and CaCO3contents. This study shows that, under the rainfed conditions
of semiarid Aragon, NT reduces the susceptibility of soil surface to crusting and water erosion as compared to CT
systems.
© 2012 Elsevier B.V. All rights reserved