[Edit of June 18: Giants confirms that he uses a displacement mapping technique to achieve his goals. Nevertheless, if the ground will have good relief, it will not be deformable for all that under the wheels of the tractor. But this technique puts the game on the right track.]
Have you seen this story on the Farming Simulator instagram account ? It displays the American farmhouse in the background of a freshly plowed field. Obviously the ground has changed a lot, showing a much more marked relief. It is therefore very likely to have terrain and earth effects totally in 3D, and why not, as a result, a deformation of the terrain under the wheels of the machines. Let's cross as many fingers as possible!