Traffic and tillage damage soil biota

Reducing or avoiding tillage has often been shown to be beneficial for soil biota, but less attention has been paid to the effects of field traffic. Traffic is unavoidable in mechanised cropping, so the objective of this study was to compare wheel traffic and tillage effects on soil biota in a grain cropping system, with particular attention to earthworms. The study was carried out on an alluvial soil in southern Queensland, using a pre-existing site with main treatments of conventional and zero tillage management, with six replicate plots. These were randomised over four blocks, two of which were double cropped and two annually cropped, with each plot split into annually wheeled or non-wheeled (i.e. controlled traffic farming, CTF) sub-plots. Most soil biota were assessed at intervals of approximately 7 weeks from August 1999 to June 2001 (13 times), taking 3 samples/plot to a depth of 15 cm with a 15 cm soil auger. Soil water content was sampled, with earthworms and macrofauna counted after sieving in the field, and before laboratory assessment of other soil biota. Microfauna, soil bulk density and soil organic matter were assessed at 4-month intervals (6 times). Incidence of earthworms was significantly greater under zero tillage (61%) than conventional tillage 35%), and greater under controlled traffic (55%) than wheeled soil (41%). Overall mean earthworm populations in controlled traffic zero tillage, wheeled zero tillage and controlled traffic tilled soil were consistently greater than those in wheeled tilled plots by mean factors of 7.7, 2.9 and 2.6 respectively but the absence of statistically significant population results has prompted reflections on the methodology used here. Arthropod populations demonstrated a smaller but generally similar mean treatment response, but microfaunal response was small. Soil water content also appeared to have a large impact on earthworm populations in the absence of tillage and traffic effects, and larger earthworm populations were observed in annually cropped plots. In subsequent exploratory field trials, more and larger earthworms developed rapidly in response to high levels of surface mulch. These results confirm anecdotal reports of improved “soil health” following CTF adoption. Elsewhere, CTF has been shown to improve infiltration rates, plant available water and crop yields, while reducing soil emissions, denitrification and power requirements. CTF is a solution to the productivity and environmental damage caused by heavy farm machinery, and its acceptability has been demonstrated now by widespread adoption in Australian grain production. • Earthworm incidence in CTF soil was double that of tilled, wheeled soil. • Tillage impact on earthworm incidence was slightly greater traffic impact. • Mean earthworm population in CTF was > 7 times that of tilled wheeled soil. • Sample size suspected as the issue in earthworm population statistics.