Effects of moisture condition and freeze/thaw cycles on surface soil aggregate size distribution and stability

Wang, E., Cruse, R. M., Chen, X. and Daigh, A. 2012. Effects of moisture condition and freeze/thaw cycles on surface soil aggregate size distribution and stability. Can. J. Soil Sci. 92: 529-536. Freeze/thaw cycles can affect soil aggregate stability. which in turn impacts wind and water erosion. The objectives of this laboratory study were: (1) to determine the effect of variable freeze/thaw cycles and soil water conditions on aggregate size distribution and stability; and (2) to evaluate differences in aggregate size distribution and stability between disturbed soil and undisturbed soil cores as affected by freeze/thaw cycles and soil water conditions. Surface soil was collected before freezing in late fall of 2009. Aggregates isolated from disturbed soil or intact soil cores were subjected to a factorial combination of 3 gravimetric water content treatments: 0.15 m(3) m(-3), 0.23 m(3) m(-3) or 0.30 m(3) m(-3), and 3 freeze/thaw treatments: 0, 3, or 9 cycles. A freeze/thaw cycle involved soil freezing at 10 degrees C for 24 h, followed by thawing at 5 degrees C for 24 h. Most aggregate size classes were affected significantly (P <0.05) by freeze/thaw cycles except for wet-sieved aggregates >5 mm. Dry-sieved aggregates were relatively more sensitive to the freeze/thaw treatment than wet-sieved aggregates. The mean weight diameter (MWD) of dry-sieved aggregates was significantly (P <0.05) greater at 0.30 m(3) m(-3) than 0.15 m(3) m(-3) water content, but the opposite trend was observed for MWD of wet aggregates and aggregate stability. There was a significant (P <0.05) response of the MWD in dry-sieved aggregates to the interactive freeze/thaw x water content effect that differed for aggregates obtained from disturbed soil and those in the undisturbed soil core, but not for the MWD of wet-sieved aggregates and aggregate stability.