SOIL FRIABILITY IN RELATION TO MANAGEMENT HISTORY AND SUITABILITY FORDIRECT DRILLING

Friability was determined for a selection of soils from the southern w heatbelt of New South Wales. Samples were taken from the surface of a range of soils that included a red-brown earth, a red earth, and a non -calcic brown soil, and covered a range of management histories. Diffe rences in soil management history explained most of the variation in f riability. Uncultivated woodland soils were highly friable in the top 20 mm [mean friability index (k) = 0.66], with intensively tilled soil the least friable (mean k = 0.05). Soils under direct drilling (DD) h ad friability similar to that from woodland sites (mean k = 0.55). Int ensive cultivation of hardsetting soils over a number of seasons decre ased their friability. Aggregates of 50 mm effective diameter had tens ile strengths that ranged from 18 to 1087 kPa at woodland and DD sites , while the tensile strengths for the same size aggregates of soils un der traditional tillage (TT) were between 1061 and 4419 kPa. Aggregate s of 2 mm diameter had tensile strengths of 17 884-63 432 kPa for wood land and DD soils, and 2012-5268 kPa for TT soil. Significant relation ships were detected between friability and the tensile strength of agg regates of 2, 20 and 50 mm size and this might present an easier means of determining friability. Friability was found to be significantly r elated to a number of other soil structural properties, including hydr aulic conductivity, bulk density, organic carbon, aggregate stability, and sorptivity. Friability might be a useful indicator of the suitabi lity of soil structural condition for crop establishment by direct dri lling. Soils with low friability appear difficult to direct drill succ essfully; this reduces the management options available for their amel ioration. Further work is necessary to relate friability directly to s eedbed conditions following direct drilling and subsequent plant emerg ence and growth, and to establish firmly the wider applicability of re lationships between friability and other soil structural properties.