EFFECTS OF ANT HILLS ON SOIL PHYSICAL-PROPERTIES OF A VERTISOL

The effects of ant hills on soil physical properties of an intensively cropped Vertisol of eastern Australia were studied in a 1 ha site loc ated at Narrabri, New South Wales, during the summer of 1993. Prior to soil sampling, number, height, and location of ant hills at the study site were determined. Soil was sampled to a depth of 100 mm from ant hills located on ridges and in furrows, and from surrounding soil. Soi l properties determined were, coarse (particle diameter of 212-2000 mu m) and fine (particle diameter of 53-212 mum) particulate soil organic matter (SOM), dispersion index, plastic limit, particle size distribu tion, soil reactivity (a measure of the self-mulching ability), soil a ggregate density and associated shrinkage indices. A total of 62 ant h ills were observed in the study site with approximately equal numbers occurring in ridges and furrows, although no ant hills were found in w heel-tracked furrows. Compared to surrounding soil, ant hill soil was less reactive, had more coarse and total particulate SOM, lower fine p articulate SOM/coarse particulate SOM ratios, greater sand and lower c lay contents, lower plastic limit, and lower soil density (in dry soil ) and greater slope of residual shrinkage in the specific volume-soil water content relationship.