The influence of dispersible clay and wetting/drying cycles on the tensile strength of a red-brown earth

The tensile strength of aggregates is a dynamic property under field conditions and for any given soil reflects the integration of processes leading to a strengthening and weakening of failure zones. The objectives of this study were to determine if variation in the tensile strength of natural aggregates from a red-brown earth could be related to the combined effects of (a) conditions favouring dispersion of clay and a subsequent increase in strength by cementation on drying and (b) wetting/drying cycles which would result in a decrease in strength. Aggregates were collected from the A horizon of different long-term rotations. The seasonal variation in tensile strength was assessed using data collected in 1988 and unpublished data which had been collected annually between 1978 and 1981. Trends in tensile strength over 5 years confirmed the importance of an interaction between climatic conditions which could lead to increased dispersion of clay and wetting/drying cycles. The extent of weakening of failure zones by wetting/drying cycles varied with the rotation. The nature of the impact of cropping history on tensile strength was dependent on antecedent climatic conditions.