Subsoil loosening does little to enhance the transition to no-tillage on a structurally degraded soil

Abstract

Long-term cropping with conventional cultivation on New Zealand’s easily compacted soil causes soil structure degradation. The objective of this study was to ascertain if soil physical properties, and crop establishment and yield could be improved by subsoil loosening in the first year of conversion from conventional tillage to no-tillage. Plots on a Milson silt loam (Argillic Perch-Gley Pallic Soil, Typic Ochraqualf) were Paraplowed (PP), straight-legged subsoiler (SL), mole ploughed (M), or left as non-loosened controls (C) in the autumn of 1997. Forage brassica was sown with a Cross-Slot™ no-tillage drill. Wheat was established on the plots in the spring of 1997. Subsoil loosening resulted in some transient improvements in measured soil physical properties. Initially, subsoil loosening significantly reduced soil strength. Shortly after subsoil loosening, cone indices showed disruption to 300 mm with PP, 350 mm with SL and 100 mm with M. About 80% of profile cone indices from the PP and SL treatments were less than the critical value of 2 MPa compared to 48% for C and M. At 267 days after subsoil loosening, PP continued to have significantly lower cone index values than C and M. In May, the bulk density of PP plots was significantly lower than SL, M and C although reconsolidation in all plots was observed 9 months later after the wheat was harvested. Air permeability for PP, SL and M was significantly greater than C in June. Subsoil loosening did not increase plant populations or yield of the brassica or wheat crops. Vertical rooting depth was greater in the PP treatment. Few significant differences in wheat rooting patterns were found at depth.