I would expect that if big farm tractors came out with DEP or DEF then the first thing the farmer would do is unhook all the smog stuff just like folks did when cars first came out with anti-smog pumps and catalytic converters. Spending money on off road equipment to reduce particulates to me is a waste and that money should be spent on developing more fuel efficient, less polluting ON road vehicles. There is more pollution put into the air in wood burning for heat/cooking, burning off cane fields, wheat fields etc than all the tractors in the world produce.
I am all for saving fuel, however most of the stuff I am reading about now cost us in fuel consumption and in effect may be raising the pollution levels rather than retarding them. The American automobile is at least 20 years behind European standards for MPG, some of it due to our demand for 800 pound feet of torque in our daily drivers but others in just plain manufacturer negligence in using the latest technology. Ever notice that everytime an new standard for mileage is set the auto makers complain about not being realistic and cant be done, but always meet the goal. I hate to say more tax, but It is time for America to match world standards for engine size and performance and make the gas guzzler tax for engines big enough to discourage buying the 6-9 liter engines. I have done quiet a bit of working in foreign countries and can tell you that many of them have no large than 2.5L engines and most places the engines are all diesel and easily get 40+ MPG in a family sedan. I drove a Jaguar station wagon in Scotland that averaged 50 MPG and ran like a scalded dog but it had a 6 speed std, turbocharger and 2.5L diesel engine. Why cant we buy something like that here? (MPG rating not necessarily a Jag)