The influence of tillage practices on soil macrofauna in a semi-arid agroecosystem in northeastern Australia

Soil-dwelling invertebrates were sampled over a 5-year period in a study comparing zero, reduced, and conventional tillage practices for grain crop production on a vertisol in semi-arid northeastern Australia. Soil animals were classified into ecologically distinct functional groups (herbivores, detritivores, and predators); ants and spiders were categorised separately. Zero tillage generally had the highest population densities of detritivores and predators, while conventional cultivation had lowest abundance in these groups. Numbers of herbivorous soil insects were similar between tillage treatments at each sampling time. Numbers within each functional group fluctuated over time, with low population densities coinciding with periods of low rainfall. It is hypothesised that the retention of crop residues on the soil surface in zero tillage, favours decomposer and predatory soil fauna, in contrast to conventional disc ploughing where stubble is buried soon after harvest. The density of predators was correlated with density of detritivores in zero tillage ( r 2 = 0.45, P < 0.04). Zero tillage is promoted as a soil conservation practice in the semi-arid tropics. Zero tillage may further increase the ecological sustainability of agroecosystems by maintaining high populations of soil-ameliorating fauna, and predators of insect pests.