Is it more conservative to use the crab steering during sugar beet harvesting? A case study from Lower Saxony, Germany

Sugar beet is one of the crops grown in Germany with the highest intensity of traffic on the field. Not only are there very high numbers of passes by the machines during the season, but the sugar beet harvesting vehicles are also among the largest and heaviest machines in use in Germany. The heavy harvesters are also used elsewhere in the world. In order to avoid multiple passes with the heavy wheel loads, the machines can often offset their rear axles parallel to the direction of travel - the so-called crab steering (CS). This distributes the load over a larger area, but also means that more area is covered in the field. This study examines whether the distribution of wheel loads over a larger area using CS shows a significant difference in soil settlement and deformation compared to traffic without the use of crab steering (wCS). Different moisture contents of the soil are taken into account. The model named FiTraM was used to model the traffic. The calculation of the soil deformation is based on empirical formulas, which are specially adapted to this field and the harvester. The subsoil in particular is considered, as soil deformation should be avoided there, since it is difficult and cost-intensive to repair. The results show that there are no significant differences in the distribution of soil deformation between CS and wCS.  In general, the moisture content of the soil determines the extent of deformation. In moist to very wet conditions (approx. 35 - 37 Vol-%), the first pass already achieves such a high degree of soil deformation that it should be avoided in practice. When the soil is dry (approx. 25-30% by volume), no soil deformation occurs in the subsoil in any of the variants - only slight deformation occurs in the topsoil. There are likewise no significant differences between the two traffic variants between 31 and 34 Vol.-% soil moisture. In summary, it can be assumed that a wheel or axle of the beet harvester is already so heavy that it makes little difference whether the machine is running in CS or not. The limiting factors are the total weight and the soil moisture content during traffic.