Untitled

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 cm 3 ) and aggregates (between 2 and 20 cm 3 ) 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. RESUMENLos Andisoles cubren aproximadamente el 50-60% de los suelos arables en Chile. La alta porosidad de los suelos volcánicos cambia continuamente, debido a estreses mecánicos e hidráulicos, que pueden conducir a un aumento de la vulnerabilidad a la sequía en cultivos, a pesar de que la precipitación excede 2.000 mm anuales. El objetivo de este trabajo fue describir el comportamiento de contracción de los suelos volcánicos en función del uso del suelo y de la escala de muestreo. Para describir el efecto de los diferentes usos de suelo (bosque nativo, praderas de 1 y 50 años) sobre el comportamiento de contracción de un Andisol a diferentes escalas, se recolectaron muestras de suelo no disturbadas (230 cm 3 ) y agregados (entre 2 y 20 cm 3 ) a profundidades de 5, 20 y 40 cm. La masa y la deformación de los agregados y las muestras de suelo se registraron a diferentes contenidos de agua. La contracción de los agregados se midió usando la técnica de resina Saran. Para caracterizar la contracción se determinó el coeficiente de extensibilidad lineal (COLE) y el índice de contracción de los poros (PSI). La intensificación del uso del suelo induce una disminución de la porosidad total (TP) y del PSI registrado a 5 cm de profundidad: TP en un 7% y PSI en un 38% de NF a P50. Esta de...