The effect of ant biopores on water infiltration in soils in undisturbed bushland and in farmland in a semi-arid environment

Data were collected on the morphology of selected ant species' nests in farmland and naturally vegetated environments on two contrasting soils. The majority of ant nests have one central channel or biopore with chambers branching off the channel. The ant biopore ranges in diameter from 1-200 mm and can extend to depths of 60 cm below the soil surface. The nest entrance or biopore remains open virtually all through the year. Biopore densities range from 0.7 to 1.9 biopores m - 2 in the various habitats with lower biopore densities in grey sandy loam compared with yellow sand sites regardless of land use. The effect of ant biopores on water infiltration was measured in situ using the disc permeameter at negative ( - 5, -10, - 40 mm) tensions and at positive ( + 10 mm) pressure. The effect of ant biopores on steady-state water infiltration rates was not significant at -10 and - 40 mm negative tensions. However, when tensions were raised to - 5 mm there was a detectable difference between water infiltration rates over the control area and the rates recorded over ant nests. But it was only under positive pressure that water infiltration over ant nests was significantly greater than the control soil. Hence ant biopores will only transmit water down the soil profile when the soil is saturated and water is ponding on the soil surface.