Abstract
The size of agricultural machinery has been increasing in the last decades. The magnitude of the wheel loads is now exceeding the limits for sustainable agriculture, and soil compaction has become a major concern. Soil compaction can be defined as the decrease in soil porosity and increase in density when stresses are applied. It has numerous adverse effects, from reducing crop yields due to root impedance or decreased nutrient uptake to increased greenhouse emissions and soil erosion. Both topsoil and subsoil compaction have detrimental effects, but whereas tillage operations can easily fix topsoil compaction, subsoil compaction can last for decades. Subsoil compaction is caused by heavy wheel loads; thus, there is a tendency toward recommending lightweight machinery for protecting the soil. In addition, the automation of agriculture is occurring at a fast pace, and companies and universities are developing lightweight autonomous robots to work collaboratively in the fields in fleets or swarms. Working in fleets could solve operational and productivity challenges but at the expense of increasing field traffic and repeated wheeling.
One of these autonomous field robots is Robotti, which is developed by the Danish company AgroIntelli. Robotti is a 4WD, relatively lightweight autonomous field robot (3000 kg) with two 55 kW engines and multiple sensors capable of doing crop monitoring operations and light tillage. It is entirely driverless, thus having a particular design that differs from traditional standard tractors. Robotti can also work in fleets and on the field for up to 60 hours (depending on the version); thus, intensive traffic is expected. Within this context, this project aimed to study the impacts of Robotti on soil properties. For this purpose, a series of studies were conducted aiming to quantify (i) the stresses from Robotti while repeated wheeling, (ii) the impacts of those stresses on soil physical properties, and (iii) the evolution of soil structure after using Robotti for multiple operations during a season.
Due to its suspension design and lifting capacity, it was found that the wheel load was not evenly distributed among the four wheels and that it changed considerably from static to dynamic conditions during repeated wheeling. The changes in dynamic load did not allow the correct adjustment of tire inflation pressures necessary for the tire to work correctly. Thus values of mean ground pressures were found in the range of larger and heavier tractors than Robotti. This high mean ground pressure caused significant (but not critical for crop growth) topsoil compaction, affecting pore geometries and functionality, especially gas and water transport. In addition, thanks to its lightweight, the simulated Robotti stresses for different situations, implements, and fields did not reach subsoil depths. Thus, despite affecting the topsoil, Robotti showed promising results in protecting the subsoils effectively.
Although traffic should still be limited to avoid multiple passes in the same places on the fields, the quantified impacts from intensive traffic with Robotti showed generally positive results. In a field experiment covering a seven-month growing season, preliminary biological activity was observed using X-ray CT images from soil samples taken in compacted wheel tracks. This activity was observed despite soil regeneration mechanisms not being the most active during those months (October – May). Therefore, besides limiting damage to the subsoil, the impacts on the topsoil might be alleviated faster than for large machinery due to its limited extent. Future studies using lightweight machinery must include assessing potential soil recovery times over extended periods.
The weight imbalances and high mean ground pressures that result in topsoil compaction could be fixed by changing the suspension system and equipping slightly wider or bigger tires than 320/65R16 models. However, more studies are needed to validate this recommendation. Robotti is already being manufactured and used in several countries. The results of this PhD work show that while the subsoil is unaffected, traffic with Robotti can cause significant topsoil compaction after several passes (between 2 and 10, depending on the initial soil strength and structure). However, the success of this technology will depend not only on its potential to prevent soil compaction but also on whether or not it can compete in terms of productivity and sustainability against traditional tractors. Thus multidisciplinary studies are needed in multiseasonal scenarios where all these aspects are considered.
One of these autonomous field robots is Robotti, which is developed by the Danish company AgroIntelli. Robotti is a 4WD, relatively lightweight autonomous field robot (3000 kg) with two 55 kW engines and multiple sensors capable of doing crop monitoring operations and light tillage. It is entirely driverless, thus having a particular design that differs from traditional standard tractors. Robotti can also work in fleets and on the field for up to 60 hours (depending on the version); thus, intensive traffic is expected. Within this context, this project aimed to study the impacts of Robotti on soil properties. For this purpose, a series of studies were conducted aiming to quantify (i) the stresses from Robotti while repeated wheeling, (ii) the impacts of those stresses on soil physical properties, and (iii) the evolution of soil structure after using Robotti for multiple operations during a season.
Due to its suspension design and lifting capacity, it was found that the wheel load was not evenly distributed among the four wheels and that it changed considerably from static to dynamic conditions during repeated wheeling. The changes in dynamic load did not allow the correct adjustment of tire inflation pressures necessary for the tire to work correctly. Thus values of mean ground pressures were found in the range of larger and heavier tractors than Robotti. This high mean ground pressure caused significant (but not critical for crop growth) topsoil compaction, affecting pore geometries and functionality, especially gas and water transport. In addition, thanks to its lightweight, the simulated Robotti stresses for different situations, implements, and fields did not reach subsoil depths. Thus, despite affecting the topsoil, Robotti showed promising results in protecting the subsoils effectively.
Although traffic should still be limited to avoid multiple passes in the same places on the fields, the quantified impacts from intensive traffic with Robotti showed generally positive results. In a field experiment covering a seven-month growing season, preliminary biological activity was observed using X-ray CT images from soil samples taken in compacted wheel tracks. This activity was observed despite soil regeneration mechanisms not being the most active during those months (October – May). Therefore, besides limiting damage to the subsoil, the impacts on the topsoil might be alleviated faster than for large machinery due to its limited extent. Future studies using lightweight machinery must include assessing potential soil recovery times over extended periods.
The weight imbalances and high mean ground pressures that result in topsoil compaction could be fixed by changing the suspension system and equipping slightly wider or bigger tires than 320/65R16 models. However, more studies are needed to validate this recommendation. Robotti is already being manufactured and used in several countries. The results of this PhD work show that while the subsoil is unaffected, traffic with Robotti can cause significant topsoil compaction after several passes (between 2 and 10, depending on the initial soil strength and structure). However, the success of this technology will depend not only on its potential to prevent soil compaction but also on whether or not it can compete in terms of productivity and sustainability against traditional tractors. Thus multidisciplinary studies are needed in multiseasonal scenarios where all these aspects are considered.
| Originalsprog | Engelsk |
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| Forlag | Århus Universitet |
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| Status | Udgivet - okt. 2023 |