Changes in the properties of a Vertisol and responses of wheat after compaction with harvester traffic

Soil compaction has been recognised as the greatest problem in terms of dam age to Australia's soil resource. Compaction by tractor and harvester tyres , related to trafficking of wet soil, is one source of the problem. In this paper an array of soil properties was measured before and immediately afte r the application of a known compaction force to a wet Vertisol, A local gr ain harvester was used on soil that was just trafficable; a common scenario at harvest. The primary aim was to determine the changes in various soil p roperties in order to provide a "benchmark" against which the effectiveness of future remedial treatments could be evaluated. A secondary aim was a co mparison of the measurements' efficiency to assess a soil's structural degr adation status. Also assessed was the subsequent effect of the applied comp action on wheat growth and yield in the following cropping season. Nine of the soil properties measured gave statistically significant differences as a result of the soil compaction. Differences were mostly restricted to the top 0.2 m of the soil. The greatest measured depth of effect was decreased soil porosity to 0.4 m measured from intact soil clods. There was 72% emerg ence of the wheat crop planted into the compact soil and 93% in the uncompa ct soil. Wheat yield, however, was not affected by the compaction. This may demonstrate that wheat, growing on a full profile of stored soil water as did the current crop, may be little affected by compaction, Also, wheat may have potential to facilitate rapid repair of the damage in a Vertisol such as the current soil by drying the topsoil between rainfall events so incre asing shrinking and swelling cycles. If this is true, then sowing a suitabl e crop species in a Vertisol may be a better option than tillage for repair ing compaction damage by agricultural traffic. (C) 2000 Elsevier Science B. V. All rights reserved.