The impact of controlled traffic farming on energy use and timeliness of field operations

The impact of controlled traffic farming on energy use and timeliness of field operations

Over the past few decades, farm machinery has simultaneously become more powerful, efficient and heavy. This increasing heaviness however, has increased the risk of deep soil compaction. Deep compaction may be rectified by deep tillage, but this is an energy-intensive process and therefore expensive. It is also often temporary as subsequent field traffic causes new compaction problems. Consequently, compaction avoidance is the best management strategy.

Controlled traffic farming (CTF) systems achieve this by confining all load-bearing wheels to the smallest possible area of permanent traffic lanes. Whilst up to 80% of cereal crops area can be wheeled in non-CTF systems each time a cereal crop is produced, the permanent traffic lanes of CTF typically occupy less than 15% of the field cropped area in well-designed grain-cropping systems.

Controlled traffic farming systems eliminate the need to disturb the compacted soil of wheel-tracks when tilling and seeding; they also minimise or eliminate the need to re-compact soft, disturbed soil for traffic and traction associated with field operations. Both aspects of CTF reduce the energy requirement of grain cropping activities. The main objectives of this work are, therefore to quantify:

- The effect of CTF on the draught requirements and soil impact (soil surface roughness and soil physical properties) of tillage and seeding operations

- The effect of driving a farm vehicle on permanent traffic lanes on the motion resistance encountered during field operations

- The implications of CTF for timeliness of field operations as motion resistance is related to trafficability and field access.

Field work was conducted during three years (2015-2017) on farms located in two Australian grain cropping regions with contrasting soils: heavy clays in the Northern region sites and lighter sands and loams in the Southern region sites. Four sites were used within each region and, where possible, experimental sites were on broadacre grain farms in long-term CTF. Northern region sites were all in Queensland, and Southern region sites were in Victoria and South Australia.

The field work was designed to assess wheel traffic effects on draught force and soil surface roughness, with replicated measurements on sweep, chisel and narrow opener tines at three depths for wheeled traffic lanes and non-wheeled traffic lanes (adjacent crop beds). Motion resistance was assessed by replicated runs towing tractors on permanent traffic lanes, adjacent crop beds and the nearest available hard surface at three different speeds. In all cases, soil textural, physical and mechanical properties were determined together with tine parameters of width of foot (tip) and rake angle, and tyre parameters including tyre inflation pressure, wheel load, tyre section width, overall unloaded tyre diameter, tyre section height and tyre deflection.

Results derived from field studies showed that wheel traffic had a significant effect on draught force for all tines and depths in CTF sites, but was non-significant in most cases in non-CTF sites. This showed that the soil of non-CTF sites was affected by historic traffic compaction therefore, in non-CTF sites there were no differences in draught forces measured in wheeled soil and non-wheeled soil. This observation confirmed that most of the compaction damage to the soil likely occurred after the first wheel traffic.

At the Northern region sites established with CTF on clay soils, draught force measurements showed that wheel traffic increased draught by up 74% and 47% for conservation tillage system (CTS) (sweep and chisel tines) and no-tillage (NT) (seeder opener tines) respectively, compared with draught forces measured on non-wheeled soil (≈2.21 vs. 3.85 kN, and 2.7 vs. 3.18 kN for CTS and NT for non-wheeled and wheeled soil, respectively). While at the Southern region sites, the draught force increased by up to 28% and 25% respectively for CTS and NT at the Swan Hill site (loam soil), compared to draught forces measured on non-wheeled soil (≈ 0.95 vs. 1.22 kN and 1.09 vs. 1.36 kN for CTS and NT for non-wheeled and wheeled soil, respectively). At the Loxton site (sand soil), the draught force increased by up 22% and 9% for CTS and NT, respectively, compared to draught forces measured on non-wheeled soil (≈ 0.94 vs. 1.18 kN, and 0.97 vs. 1.06 kN, for CTS and NT for non-wheeled and wheeled soil, respectively).

Wheeled traffic also resulted in greater soil surface roughness. The results showed that the Northern sites had 37% for NT systems and 59% for CTS and the Southern sites had 23% for NT systems and 27% for CTS.

At Northern region sites, Controlled traffic farming resulted in improved soil physical properties. The results showed that soil penetration resistance (PR), bulk density of soil (BD), soil moisture content (MC) and shear strength (SS) at depth 0-150 mm were higher (1.58 MPa, 1.19 Mg m-3, 38 % (w/w) and 0.19 MPa, respectively) and (2.18 MPa, 1.6 Mg m-3, 22% (w/w) and 0.31 MPa, ) on Permanent Traffic Lanes (PTL) for the Felton and Pittsworth sites respectively, compared with Permanent Crop Lanes (PCB), where the results were lower (1.04 MPa, 1.08 Mg m-3, 36% (w/w) and 0.06 MPa, respectively) and (0.93 MPa, 1.17 Mg m-3, 22% (ww), and 0.08 MPa, respectively), for Felton and Pittsworth sites, respectively.

At the Southern region sites of Hopetoun (VIC), Swan Hill (VIC) and Loxton (SA) respectively, results also showed that PR, BD, MC and SS were higher (3.4 MPa, 1.66 Mg m-3, 11% (w/w) and 0.21 MPa, respectively), (3.68 MPa, 1.75 Mg m-3, 13% (w/w) and 0.28 MPa, respectively) and (2.44 MPa, 1.67 Mg m-3, 6% (w/w) and 0 MPa, respectively), with PTL, compared with PCB where the results were lower (1.91 MPa, 1.44 Mg m-3, 10%(w/w) and 0.09 MPa, respectively),(2.3 MPa, 1.32 Mg m-3, 8%(w/w) and 0.13 MPa, respectively) and (1.20 MPa, 1.54 Mg m-3, 5% and 0 MPa, respectively).

Motion resistance (MR) results showed that wheeled traffic and ground speed both had significant effects on MR, and that traffic on permanent wheel tracks reduced MR at all CTF sites. Mean energy input to permanent traffic lane soil, that is MR on soil-motion resistance on a hard surface, was up to 23% lower in Northern region clay soils (≈9.22 vs. 11.92 kN for PTL (CTF) and non-wheeled soil (non-CTF), respectively), and up to 20% lower in Southern region sands and loams (≈10.26 vs. 12.81 kN for PTL (CTF) and non-wheeled soil (non-CTF), respectively), compared with non-wheeled soil.

Modelling of draught force and motion resistance, based on soil, tine and tyre parameters was used to validate and extend the usefulness of the field results of draught force and motion resistance. The integrated tillage force prediction model of Godwin and O’Dogherty (2007) was used to predict the draught required by the implements employed in this study. Regression analyses showed a reasonably good agreement between predicted and observed draught for the range of different tines and soil types investigated, with the exception of the Hopetoun (Victoria) site. This was because the soil of the Hopetoun site was affected by non-homogeneous compaction as a result of using different track width of equipment (incomplete CTF).

In the Northern region CTF sites, which are dominated by clay soils, model predictions of draught were within an error range between 3% and 5%, -17% and 2%, and -12% and 1% for sweep, chisel and opener tines, respectively. In the Southern region CTF sites, which are dominated by medium and light-textured soils, model prediction of draught was in the range of 5% to 26%, -13% to -8%, and -21% to -15% for sweep, chisel and opener tines, respectively.

Prediction of motion resistance was conducted with the Gee-Clough and Brixius models. Linear regression analyses showed that measured and predicted data did not correlate well, and this was observed for all soil types. But, predictions of Brixius’s model was better corresponding with most experimental data of motion resistance compared with the Gee-Clough’s model.

For timeliness implications, the results derived from this study showed that the improvement in trafficability for CTF can be up to 50% and 80% for NT and CT (conventional tillage), respectively at Northern region sites on clay soil, while at Southern region sites on medium and light textured soils, the improvement in trafficability was 38%.

The results of this study clearly demonstrate the potential of CTF to significantly reduce the energy requirements of cropping operations. The results demonstrate the validity and usefulness of the Godwin and O’Dogherty (2007) model. This study also demonstrates that permanent traffic lanes can significantly improve the trafficability of soil. These findings also confirm that CTF resultes in improved soil physical properties, which reduce the energy requirements of cropping operations including draught force and motion resistance, and improve trafficability and timeliness. These are expected to increase the sustainability of soil and enhance crop and environmental performance.