Residual effects of a slant-legged subsoiler on some soil physical conditions and the root growth of spring barley

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Abstract
Summary: Soil disturbance caused by a slant-legged subsoiler (Trade name, ‘Paraplow’) and the duration of its effect was investigated in an experiment comparing long-term direct drilling with shallow tine cultivation and mouldboard ploughing. The ‘Paraplow’ significantly reduced soil strength, measured by cone resistance, to the depth of cultivation (33–35 cm) for up to 20 months, after which soil recompacted. The ‘Paraplow’ increased the volume of soil with cone resistance < 1·5 MPa by 52% within its working depth, compared with an equivalent depth of undisturbed soil. Contour diagrams of cone resistances clearly illustrate the patterns of soil loosening caused by the ‘Paraplow’.Measurements on soil cores (73 mm diameter × 50 mm) show that the ‘Paraplow’ did not appear to increase significantly the volume of macropores (> 60 μm) in direct-drilled soil, nor did it reduce the bulk density in the top 5 cm as effectively as the mouldboard plough.The root density of spring barley, measured at the beginning and end of tillering, was significantly increased within the horizon disturbed by the ‘Paraplow’ but below the depth of loosening there were no differences. This improvement of root growth probably resulted from an increase in the number of large pores (which could not be measured adequately in the soil cores), as well as the reduced soil strength. Better drainage of the soil loosened with the ‘Paraplow’ suggested that macroporosity was improved. The need to sample large volumes of soil to detect changes in bulk density and macroporosity is stressed.