Abstract

Andisols cover approximately 50-60% of the arable land in The high porosity of volcanic soils changes continuously due to mechanical and hydraulic stresses, which can lead to an increase of drought vulnerability in crops, even though precipitation exceeds 2,000 mm annually. The aim of this work was to describe the shrinkage behaviour of volcanic soils as function of land use and aggregate scale. To describe the effect of different land uses (Native Forest, 1 and 50 years old grassland) on the shrinkage behaviour of an Andisol at different scales, undisturbed soil samples (230 cm3) and aggregates (between 2 and 20 cm3) were collected at 5, 20 and 40 cm depth. The weight and deformation of aggregates and undisturbed soil samples were registered at different water contents. The aggregate shrinkage was measured using the Saran resin technique. The coefficients of linear extensibility (COLE) and pore shrinkage index (PSI) were used to characterize the shrinkage behaviour. The intensification of the land use induced a decrease in the total porosity (TP) and total PSI measured at 5 cm depth: TP by 7% and PSI by 38% from NF to P50. This soil deformation occurred not only due to soil compaction but also as consequence of an intense drying. When land use changes from native forest to pasture, soils dry out more intensively, leading to smaller shrinkage properties, e.g. COLE decreased as a result of the increasing bulk density, which is also related to the amount of allophane. The smaller aggregates presented higher bulk densities than soil cores. Finally, significant scaling relationships were not observed for initial soil volume and COLE, therefore, further conceptual and experimental development are required to understand these scaling effects.