Effect of antecedent matric potential on the stability of soil aggregates subjected to cyclic freezing and thawing as evaluated by three structural indices

Abstract

Summary Using three texturally-contrasting soils from Modena, Vicarello and Cremona in North-central Italy, the extent to which the antecedent contents of soils predispose them to frost-induced alterations in aggregate stability were studied using three procedures for evaluation of structural stability. Antecedent moisture content was expressed in terms of matric potentials. The three indices, mean-weight diameter of water-stable aggregates (MWD), specific dispersion energy of soil clods (D) and clay dispersion index (CDI) were consistent in placing these soils in the following order of structural stability: Modena (clay) > Vicarello (clay loam) > Cremona (sandy clay loam). This reflected increasing CaCO 3 content and decreasing sand content and SiO 2 /Al 2 O 3 ratio. However, the sensitivity of these soils to cyclic freezing and thawing, expressed in terms of a frost-susceptibility factor (Fi) decreased with decreasing silt + clay content and varied in the order, Cremona (5.7%) With cyclic freezing and thawing treatments, moisture contents between saturation (0.0 MPa) and the −0.033 MPa matric potential reduced substantially MWD and D. At the −1.5 MPa and airdry conditions, little changes in these two indices were observed. The microaggregation index, CDI, did not reflect the effect of moisture content on structural stability.