In cropping soils compaction is caused by compression from agricultural machinery traffic with the compacted layer forming between 10 and 40 cm (Davies 2007). Compaction results in decreased pore space around the root zone of the plant, creating an environment high in density and strength. Less pore space reduces soil water holding capacity, and water that is available to plants is held more tightly in the smaller pores (Hamza and Penny, 2005). Therefore the plant has to exert more energy to extract water rather than using that energy for producing yield. Low soil porosity can also be detrimental to soil biological activity. There are limited options for ameliorating subsurface compaction apart from physical tillage of the compacted zone. However, management practices can be implemented to reduce or avoid subsurface compaction.
Figure 1: A crop being harvested with the chaser bin driving on permanent wheel tracks. (Photo by Paul Blackwell, DAFWA).
More precise operations and segregation of the paddock into different zones (traffic lanes, row, inter-row, ‘soil type’) allow the farm and regional environment to benefit from:
All these benefits will result in improved crop yields (table 1). An added benefit of CTF if removing subsurface or seedbed compaction through deep ripping, is that soil will continue to remain loose and friable for many years after natural ‘settling’ as soil is not being trafficked back to its original compacted state.
Table 1: Grain yield and value from 9 m wide harvester cuts for normal (NT) or controlled traffic (CT) after initial deep cultivation in 1997 at Mullewa, Western Australia (average annual rainfall = 320 mm).
CT yield (t/ha)
NT yield (t/ha)
CT vs NT (%)
Grain $ at gate
New approaches to avoiding the risks of soil loss from heavy rainfall for downhill controlled traffic systems are being evaluated. Widespread use of techniques such as tramline farming, controlled traffic and auto-steer means that working on the contour is often not practical. Queensland research has shown that controlled traffic systems working downhill on slopes up to 2% can reduce the incidence of gully erosion from intense storms compared to contour planting, provided there is good ground cover and water infiltration.
The greatest runoff rate at Pindar and Buntine paddocks in Western Australia was from tramlines in a downhill working system (slopes of 1.5–3%), and the least runoff from a deep cultivated soil between the tramlines, where compaction had been removed. As the tramlines cover only 15–20% of the overall paddock area, there was less runoff from downhill working than across slope system provided the soil was not compacted. Technical difficulties of grass weed control and rutting in permanent tramlines still persist, but chaffy (furry) tramlines, zero tramline disturbance and better tyre choice may offer improvements, as well as improved management of water flow.
Where the soil is compacted or groundcover levels are low (especially after grazing), runoff from downhill systems can be larger than when working across the slope. This indicates a need for appropriate earthworks to control the rate of overland water flow and minimise the risk of soil erosion from intense rainfall events.
Technical difficulties of grass weed control and rutting in permanent tramlines still persist, but chaffy (furry) tramlines, zero tramline disturbance and better tyre choice may offer improvements, as well as improved management of water flow.
Davies S (2007). Subsurface Soil Compaction. Fact sheet for Soil Quality website.
Hamza M and Penny S (2005). Improving compacted soils in the eastern wheatbelt. Department of Agriculture and Food, Western Australia Farmnote No. 53/2005.
The Controlled Traffic Farming website.
The NSW Department of Primary Industries maintains soil information resources on the website.
The National Soil Quality Monitoring Program is being funded by the Grains Research and Development Corporation, as part of the second Soil Biology Initiative.
The participating organisations accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.