摘要：The form and stability of soil structure are important for soil aeration, storage and transmission of water and nutrients, as well as root penetration and development. Soil aggregation and tillage-induced changes to soil structure are not well understood in volcanic ash soils. The objective of this study was to describe aggregate stability, aggregate size distribution, and porosity, and to examine their relationships with some soil properties, and their changes induced by arable cropping. Soil samples (Humic Udivitrand, USDA Soil Taxonomy) were collected from three sites under Pine forest, and three sites on arable land. Aggregate stability is moderately high (45-80%) and MWD indicates that soil aggregation is moderately stable to stable. All soils show a relative decline in aggregate stability under long-term (50 years of potato) cropping, because of macroaggregates breakdown, while microaggregates remain constant. Soil porosity is variable (44-91%) but generally higher in topsoil (65%) than in subsurface horizons (56%). Porosity decreases under cropping as a consequence of macropores (> 10 μm) reduction produced by macrostructure disintegration. Soil aggregation and porosity changes are mostly correlated to total OC and fine sand contents, but are not always appreciable because of the complexation of organic carbon with amorphous forms of Al and Fe and a strong microstructure, which protect these soils from degradation, even after long-term cropping
其他摘要：The form and stability of soil structure are important for soil aeration, storage and transmission of water and nutrients, as well as root penetration and development. Soil aggregation and tillage-induced changes to soil structure are not well understood in volcanic ash soils. The objective of this study was to describe aggregate stability, aggregate size distribution, and porosity, and to examine their relationships with some soil properties, and their changes induced by arable cropping. Soil samples (Humic Udivitrand, USDA Soil Taxonomy) were collected from three sites under Pine forest, and three sites on arable land. Aggregate stability is moderately high (45-80%) and MWD indicates that soil aggregation is moderately stable to stable. All soils show a relative decline in aggregate stability under long-term (50 years of potato) cropping, because of macroaggregates breakdown, while microaggregates remain constant. Soil porosity is variable (44-91%) but generally higher in topsoil (65%) than in subsurface horizons (56%). Porosity decreases under cropping as a consequence of macropores (> 10 μm) reduction produced by macrostructure disintegration. Soil aggregation and porosity changes are mostly correlated to total OC and fine sand contents, but are not always appreciable because of the complexation of organic carbon with amorphous forms of Al and Fe and a strong microstructure, which protect these soils from degradation, even after long-term cropping
关键词：Andisol; estabilidad de agregados; suelo forestal
