Blade loosening creates a deeper and near-stable rooting zone that raises the productivity of a structurally unstable texture contrast soil

Abstract

Improving the workability and raising the productivity of structurally weak and/or dispersive texture contrast soils has been the objective of many research projects. These have used applications of gypsum, with and without ripping the top 300–400mm depth of soil, and responses have been moderate and short lived. The approach taken in the present study was to ameliorate the soil by a combination of subtle soil disturbance to a depth of approximately 300mm using a specially designed blade loosener, with controlled traffic and no-tillage crop establishment practices. The aim was to use the roots of the stimulated plant growth to stabilise a loosened and deepened root zone. Comparative conditions in the 0–500mm depth of soil in blade-loosened and normal seedbeds were monitored over three very different growing seasons (2001, 2002 and 2003) using chemical analyses, bulk density (BD), penetration resistance (PR) and soil moisture content measurements. Productivity was monitored by dry matter and grain yield, and profitability by gross margin analyses. Structural stability of the rooting zone soil, or the lack of it, was shown to be a consequence of how the seasonal dynamics of the profile moisture content affected the probability of waterlogged surface soil conditions. In the normal seedbed (control) the surface soil quickly reconsolidated (BD ≥1500kgm–3), and subsoil BD (BD ≈ 1800kgm–3), PR (≥1.8MPa) and percentage saturation (≥95%) remained at levels restrictive of root growth. Conversely, the same properties in the surface and subsoil of the blade-loosened seedbed remained at levels conducive to unrestricted root growth (BD ≤1400kgm–3, PR ≤1.1MPa, saturation ≤70%). The blade-loosened treatment was substantially more productive (average grain yield increase 35%; P<0.05) and profitable (average gross margin increase 56%).