I don't know a lot about tractors, but I know quite a bit about fuel.
Low Sulfur Diesel has higher lubricity than kerosene. In my younger days I fueled aircraft and managed QC for the fuel facility I worked at while working on my pilot ratings. The old ford fuel trucks we ran loved running Jet-A mixed with diesel in the winter when straight diesel would gel. Jet-A is essentially kerosene. We would run straight diesel in the summer because mixing it was a great way to burn up piston rings, fuel pumps, etc.
They're probably doing this thinking it helps with the reduced lubricity of modern low sulfur fuel, but they're exaggerating the problem by adding kerosene.
