INTERACTIONS BETWEEN SOIL TYPE AND TILLAGE LEVEL IN A DRYLAND SITUATION

Soil physical conditions were measured under conventional, minimum and zero soil disturbance cropping systems. Seedbed differences were small in soils cropped after stubble, but significantly different on light sandy soils cropped after pasture. Soil resistance to penetrometer was significantly higher at 10 cm with direct drilling. Soil porosity, and properties dependent upon it, varied more with tillage level on loamy sand than on clay loam soil. Root distributions and associated soil interactions were measured by means of soil cores. Root growth rate varied with soil texture and with tillage level. Soil water contents were at matric potentials well above -1-5 MPa at 6 weeks, but root depth in the finer-textured soil was only half that of the loamy sand. Root extension rate was restricted by soil strength rather than water shortage in the early part of the growing period. Direct tillage with a triple disk drill reduced root extension rate at both sites in the early phase. Evidence of a compaction pan on the loamy sand is presented. © 1979, CSIRO. All rights reserved.