Self-repair of compacted Vertisols from Central Queensland, Australia

Vertisols have the inherent ability to self-repair because of high clay contents and clay type that govern volume change. A study was undertaken to correlate soil inherent properties with two indicators of structure improvement based on tensile strength and clod porosity of compacted soil cores before and after wet/dry cycles. In order to minimize inter-soil differences Vertisols under similar cropping regimes and from the same climatic region in Queensland, Australia were selected. A soil repair index (RT(1)) based on compressive strength of soil cores was related to soil inherent properties and shrinkage indices, COLESTD and LSMOD using multiple regression. Results showed that compressive strength of soil cores after a single wet/dry cycle after compaction was sufficient to rank Vertisols in terms of their capacity to improve structure after compaction. Clay content and clay activity (CEC/clay) on their own were poor indicators of soil repair. Fine sand was shown to be an important component in the repair process. LSMOD and COLESTD predicted RT(1) equally well and indicated that Vertisols with COLESTD values > 0.15 and LSMOD > 12% would be expected to have sharper reductions in tensile strength compared to those with lower values after just one wet/dry cycle. Clod porosity was poorly related to soil inherent properties.