Agree with everyone about DPF should regen every 20-50 hours or so.
That said, there seems to be a common misconception here between DPF (diesel particulate filter) and DEF (Diesel exhaust fluid). From 2013 (I believe as I’m new to this), tractors over 25 HP are subject to tier IV emissions which in most cases means that these tractors have a DPF. The DPF in layman’s terms, collects diesel particulates and once it get full enough, the engine throws extra fuel into cylinders to increase exhaust gases to burn out the particulates in the filter. This process is called regeneration, or regen.
On the flip side, I didn’t research this as it wasn’t applicable to be but from reading this thread, tractors over 75 horsepower may have DEF along with a DPF. This DEF is injected into the exhaust to form a chemical reaction with the NOx gases to convert them into elements (I think water and…. Something else, not sure) to essentially help with greenhouse gases.
Hope that clears the air regarding the emissions. If it’s anything like trucks, the DEF system is usually the more unreliable side to the emissions components. Trucks also have the SCR (selective catalytic reduction) which is part of the DEF, not sure if that’s the case for tractors.