Comment by bri3d

DPF (Diesel Particulate Filter) and SCR (Selective Catalytic Reduction, which uses DEF, Diesel Exhaust Fluid) are two mostly different systems. DPF traps soot in a filter which then burns the soot off into gas later (regen). SCR reduces NOx using urea.

This is important to know in the context of tractors because in the US, 25-74hp tractors generally need only DPF without SCR (there are basically three bins depending on horsepower level). This makes these midsized tractors a bit of a sweet spot for a lot of tasks; of course, you still have to deal with regen (which is where the DPF gets heated up to convert trapped soot into gas), which is annoying, but you at least don't have to fill up with DEF or risk the DEF injection system failing.