*Note - this report may contain independently supported projects which complement the work in this GRDC research program.

Take home messages

• Traffic can depress crop yield on clays gravels and loams by up to 60%. Similar yield depression was shown with pre-seeding traffic. Financial benefits of $5 to $20/ha are possible in the first year of adoption of tramline farming on clay or gravel soils following deep ripping.
  
  
• It is possible to design a simple and practical solution to provide sound statistical analysis of tramline benefits as used in these trials.

Aims

• To quantify the effects of agricultural traffic on crops yields for 'heavy soils' i.e. other than sands.
  
  
• There is a need to develop a simple on-farm trial technique to replace high management requirements of small plot trials comparing whole systems (e.g. normal vs controlled traffic). One such technique was used in these trials.

Methods

Four sites were set up with deep cultivated zones parallel to the direction of sowing the paddock and cropping traffic applied at right angles to the direction of sowing. This strategy helped distinguish trial traffic from other traffic in the paddock. Colour coded sighting posts were installed in the fenceline to assist traffic navigation; in one case the autosteer guidance system was used. The traffic varied from site to site according to available farm equipment The analysis was therefore not comparative between specific traffic operations at different sites but expressed as whole effects of a cropping system for those circumstances at each site.

Traffic effects on the soil were measured by wheel sinkage and visual tactile methods (McKenzie 2001). Traffic effects on the crop were measured with hand harvesting in and between the wheelmarks as well as some plant tissue analysis and dry weight measurement at one site showing symptoms of waterlogging. Standard methods for soil pH EC and dispersibility as well as the visual-tactile SOILpak analysis assessed deep ripping effects and the original soil condition. SOILpak is a best practice management manual produced by New South Wales Agriculture. The manual provides farmers with information on the skills required to assess the condition of the soil (predominantly soil structure) and understand the management options for maintaining or improving soil conditions.

Calculations of Tramline Farming (TLF) benefits were made by using the yield depressions by traffic and assumed traffic patterns (refer to extended paper). The financial value of the grain yield differences is calculated for each site using $180/t for malting barley at Esperance and $200/t for wheat at the other sites.

Results

All sites had SOILpak scores that suggested some poor structure (Table 1). The Esperance site at 10-20 cm soil depth had a dense soil fabric between the gravel stones and showed severe surface waterlogging in the wheelmarks during the winter; chlorosis was also noticeable in the unripped areas.

At Esperance the cropping traffic on ripped or unripped soil reduced plant growth and nitrogen uptake by about 50% and the growth and nitrogen uptake of the crop on ripped soil (10 kg N/ha) were about twice that of the unripped. Nasal evidence of waterlogging was also found at 0-10 cm during soil examination in winter (Table 1).

¹ McKenzie (2001) < or =1 needs improvement.
² Spontaneously dispersive (Emerson test).
³ 70% gravel from 15 to 50 cm.
⁴ Winter waterlogging and 'septic tank' smell.

Wheeling conditions at all sites were moist except for the spreading treatment at Geraldton. Wheel sinkage was up to 15 cm at wet deep ripped locations at Esperance and Lake Varley. The conditions at each site were not alike and the cropping traffic had differences between sites. However the range of equipment and conditions represent a wide range of conditions found in the wheatbelt outside the sandplain. The range of yield reductions by traffic (average 28% in Table 2) showed larger yield reductions from traffic on ripped soil (33%) than unripped soil (24%). This resulted in the average yield in the wheelmarks being very similar in the ripped or unripped condition at the same site. The yield of the treatment with all traffic equivalent to a sown tramline was not as low as anticipated.

Significant yield reductions by cropping traffic were found at all sites but weed invasion reduced the data set from the Geraldton site. The Esperance site was typical of localised areas on farm poorly drained and suffering from surface waterlogging.

* Significantly greater than unripped yield (P > 0.05).
^# 4WD truck.
¹ Post seeding like the effect of a tow-behind air seeder box.
² Dry surface conditions.
³ Identified in 2002 stubble for trial site.

Effects of traffic on grain quality were less than seen in the trials on sand at Mullewa in 2002. At Esperance however the grain from outside the wheelmarks (GOW) had 12% protein; 55.4 colour units; 70.3 kg/hL and 2.5% screenings; traffic may have increased screenings by 2%.

At Lake Varley the GOW was 10% protein 81.7 kg/hl and 0.1% screenings; traffic had no effect.

At Wubin the GOW was 12.3% protein 81.2 kg/hl and 1.3% screenings; traffic increased screenings by 2% and reduced hectolitre weight by 3 kg.

At Geraldton the GOW was 9.1% protein 79 kg/hl and 1.8% screenings traffic had no effect. Grain quality was not used to help quantify the financial benefits of controlling traffic because there were so few differences.

The financial value of controlling cropping traffic was calculated from the trial results and compared to earlier trials on sand (Blackwell 2000). The financial benefits from tramline farming on clay soils in inland areas are similar to the benefits on sands such as seen in trials at Mullewa in 1999 if preceded by decompaction with deep ripping (refer to Table 4 extended paper).

The gravel soil on the south coast showed less benefit from ripping and controlling the traffic than the Mullewa site in 1999. The need for initial deep ripping to gain most benefits from the system is obvious. However it is essential to assess the soil conditions within 50 cm depth to determine the need for decompaction and the possible need for stabilisation from dispersion and structural collapse. For example at the Wubin site decompaction beyond 20 cm seems unnecessary according to the SOILpak score and the response to deep ripping at the site came from working the tines of the airseeder only to 20 cm depth.

Conclusions

Cropping traffic in one season can depress yield on clays gravels and loams by up to 60%. The yield depression of pre-seeding traffic was similar. Financial benefits of $5 to $20/ha are possible in the first year of adoption of tramline farming on clay or gravel soils following deep ripping. The larger benefit is comparable to that calculated from trials on sandplain sites. This should reassure WA grain growers of the potential benefits from tramline farming.

The trial design has proved practical executed at 4 farm locations using on-farm equipment with little supervision and no marking pegs within the paddock. The analysis has proved precise enough to compare different wheelings at most sites.

References
Blackwell P. (2000). Improving sandplain cropping systems by Controlled Traffic. Agribusiness Crop Updates 2000; Observation City; Perth February.
Blackwell P. Webb B. Lemon J. and Riethmuller G. (2003). TRAMLINE FARMING; pushing controlled traffic further for Mediterranean farming systems in Australia. Proc. 16th Int. Conf. Soil and Tillage Res. Org.; St. Lucia Brisbane July 2003.
Bakker D. Hamilton G. Houlbrooke D. and Spann C. (2002). Raised bed farming in the 2001 growing season. Agribusiness Crop Updates 2002; Sheraton Hotel Perth; February.
Hamza M.A. McConnell G. and Anderson W.K. (2002). Economics of improving compact soils. Agribusiness Crop Updates 2002; Sheraton Hotel Perth; February.
McKenzie D.C. (2001). Rapid assessment of soil compaction damage. I. The SOILpak score a semi-quantitative measure of soil structure form. Aust. J. Soil Res. 39 117-125.

Acknowledgments
Maurice Black Mario d'Antuon