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Crusting | Waterlogging | Trafficability | Compaction | Cultivation/Tillage for Broadacre Cropping

What do we mean by trafficability?
A soil is trafficable when vehicles, people or animals can pass over it without causing any damage to the soil nor impair its functions.

Trafficability is modified by the intensity of passage of the traffic (i.e. compressive forces and shear forces), and by the load bearing strength of the soil (dependent on soil characteristics and moisture content).

If a soil is to be kept biologically productive, then any compaction by the passage of vehicles or animals is undesirable.
Compaction restricts root growth, limits water and nutrient movement, and thus damages plant production. Livestock moving over a wet paddock can chop up surface soil and damage soil structure, compact near-surface layers, and even facilitate erosion and nutrient loss.

Trafficability is about getting essential movements of machines and animals across the land without causing any long term damage to the soil.

How to manage for improved trafficability?
Establish what traffic is needed.

Establish soil resistance and susceptibility to compressive and shear forces.

Determine the influence of moisture content on resistance and susceptibility.
Work to restrict traffic to times of lowest susceptibility. Know the times when the soil should not be bearing loads (see
soil strength).

Consider using sacrifice areas by geographically controlling traffic with the use of roads and fixed tracking systems in cultivated areas, ‘controlled traffic farming’ (CTF) is the term used for this approach,

What is controlled traffic farming?
In cropping systems, control traffic farming (CTF) is the restriction of all machinery to defined pathways in a paddock.

These pathways are established by either:

  1. a marker implement placed on a tractor working in the paddock and then maintained by the operators continuing to drive their machinery down the wheel marks set by the first machinery; or
  2. using a global positioning satellite guidance system (external link) to establish the pathways. The pathways are then either manually driven from then on, or auto steer machinery that tracks the same pathways is used.
To complete the process all machinery needs to be the same wheel width, a common width being used is 3 metres. By doing this all compaction and soil disturbance is concentrated into a smaller area on which crop is not grown. In a conventional farming system with cultivation practices, some form of machinery is passed over the soil 9 to 12 times per year, and 3 or 4 of these are heavy cultivation machines.

What are the benefits of controlled traffic farming?
The financial benefits of CTF include less expenses on chemicals and fertilisers on the CTF pathways, plus benefits created from less compaction, better soil structure and root growth, and improved aggregate stability so better uptake of water and nutrients and less erosion. Current evidence suggests that depending on the inherent characteristics of the soil, the simple removal of long-term compaction contributes to improving the hydraulic properties of the soil (Peries 2006).

Once established the CTF system optimises machinery operation and plant growth. Plants prefer soft soil while wheels and tracks perform best on hard soils. CTF gives the roots a well structured, aerated medium in which to grow resulting in faster growing and longer roots. A non-compacted soil is more attractive for soil flora and fauna. Growers are reporting increases and return of earthworms, termites colonies and other macro fauna.

What are the implications of poor traffic management?
Uncontrolled traffic movement over paddocks leads to
compaction that affects the ability of plants to grow to their full potential by restricting plant root movement through the soil. Soil porosity is decreased, limiting water infiltration and conductivity across the paddock.

Where is controlled traffic common in Victoria?
Controlled traffic is common in southern Australia in the high rainfall zone (> 550 mm per year), used in conjunction with permanent raised beds.
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