Reduced Tillage Increases Population Density of Soil Macrofauna in a Semiarid Environment in Central Queensland

The effects of modified tillage practices on population densities of beneficial and harmful soil macrofauna were investigated. Soil-inhabiting macrofauna were sampled during 5 yr in a field experiment on a black Dermasol and Vertisol in semiarid central Queensland. The experimental treatments were 4 tillage practices applied during the fallow periods between grain crops. Reduced frequency and intensity of tillage increased the level of crop residues providing surface cover. Zero tillage had the highest population of macrofauna (74/m2), followed by reduced tillage (50/m2), stubble mulch tillage (44/m2), and traditional tillage (31/m2). Detritivore populations also were highest in zero tillage (44/m2) followed by reduced tillage (29/m2), stubble mulch tillage (26/m2), and traditional tillage (15/m2). Earthworm populations were highest in zero tillage (17/m2) and lowest in traditional tillage (5/m2). The incidence of termite colonies was higher in zero tillage (7.0/m2) than in reduced tillage (0.9/m2), stubble mulch tillage (0.3/m2), or traditional tillage (0.2/m2). Zero tillage usually had the greatest diversity of macrofauna species. Population density of herbivores, which are generally agricultural pests, was similar in all tillage treatments. These results indicate that long-term reduced or zero tillage will not lead to increased problems with soil insect pests.