The soil-water cost of heavy machinery traffic on a Queensland Vertisol, Australia

Abstract

The development of larger, more powerful agricultural machinery to increase field efficiency has occurred in broad-acre agricultural systems, at the risk of significant soil compaction. The effect of heavy machinery on the increase in soil bulk density is often recorded as an indication of this compaction, but the soil-water effects are rarely directly measured. It is therefore important to understand the impact of soil compaction on the soil water characteristic under such machinery, which was the objective of this work. Using the John Deere 7760 (JD7760) cotton picker as a case study, a Vertisol from Jimbour, Queensland, Australia was investigated for changes in soil water potential after traffic from a conventionally and a controlled traffic farming (CTF) configured JD7760 to determine the magnitude of impact non-CTF systems have on Australian cotton production systems. Bulk density, saturated moisture content, and cracking pattern were also determined. The saturated hydraulic conductivity decreased significantly in response to traffic with the greatest relative reduction occurring in the lower depths. Bulk density increased significantly in response to traffic, with the greatest relative increase occurring nearer the surface. The cracking pattern and area of void represented by soil cracks was shown to be related to change in soil bulk density due to traffic. Plant available water was demonstrably reduced, and this significant decrease was inferred from cracking pattern analysis. Basic economics for the traffic systems are presented to provide an economic and environmental imperative to traffic system management.