Macro- and micro-aggregate stability of soils determined by a combination of wet-sieving and laser-ray diffraction

Abstract

Soil structural stability affects the profitability and sustainability of agricultural systems. Different-sized structural units have different stability mechanisms and respond differently to such external factors as rain, wind, irrigation and management. A comprehensive analysis of the soils structural stability requires its characterization at the macroand micro-aggregate scales. We determined the aggregate stability of 36 soils at the macro-aggregate scale using wetsieving methods and of 20 soils at the micro-aggregate scale using laser-ray diffraction techniques. All the tests gave consistent estimates of aggregate stability. Most soils were homogeneous and quite stable at the macro-aggregate level as determined by the "water stable aggregate" parameter, but differed significantly among them and were quite unstable at the micro-aggregate level as determined by the "mean weight diameter of micro-aggregates" parameter. Slaking induced by the fast wetting of aggregates was the main destabilizing mechanism in these soils (88% of the soils had slaking stability index values < 0.5), whereas most soils were quite tolerant to the mechanical shaking of aggregates (89% of the soils had stirring stability index values > 0.5). The combination of the macro- and micro-aggregate stability tests is a consistent way for describing the structural stability of the studied soils.