Indexes of residual shrinkage to quantify the comparative effects of zero and mechanical tillage on a vertisol

Differences in the soil physical condition of the surface layer of a Vertisol (near Warwick, Queensland) under a zero versus mechanical tillage trial were investigated by using indices derived from a limited part of the soil's shrinkage curve. Shrinkage data were generated by coating initially air-dry clods in SARAN resin, then oven-drying them in six temperature increments to 105°C. Values of both the slope and y-axis intercept of a straight-line fit to the data were significantly greater in the mechanically tilled treatment. This showed that mechanical tillage led to decreased bulk density (increased porosity) and caused the soil to have greater shrinkage potential.