Like Messicks says, over 75 use DEF; however, it is possible to meet the regs without DEF but at a performance cost. DEF allows hotter combustion which burns in ft more soot allowing a lesser, or for some, no DPF. There are trade with offs and each tractor corporation has its own plan. CNH uses a combination of everything. Soot is a much larger concern in Europe than in North America and the rational at their Stage 4, our Tier 4 final, was that DPFs would be required. The engine companies told them so. So now many do not have DPFs and very fine soot particles continue to be a problem and the EU is pushing for their Stage 5. The engine companies want North America, Japan, and other first world countries to follow slong to reduce the number of engine models.
Kubota announced their Tier 4 final larger tractors (over 75 HP) in 2014 but the M7 series is still not available in North America. It's now a year past their first promised introduction date.
The under 25 HP have been Tier 4 final since 2008. The over 25 and under 75 went Tier 4 final in 2014 (at least that's when I got my quote to replace my L5740 with a L6060. I thought, reading this forum, that the earlier tractors would hold their resale value but in my case that proved not to be true. I took an enormous depreciation hit on my L5740 when the L6060 came out do I still have the L5740. I hate the exhaust smoke. My wife can't work with me without using her rescue inhaler from m the asthma attack the smoke triggers. Same with my partner whose asthma is even worse. At least my M135GX to s clean relative to soot although the NOX is high. Due to breathing problems possibly induced by the diesel exhaust we have all relatively clean burning engines except for the L5740. Now if somebody would just give me $10k less than what a new L6060 would cost I would snap the offer up in an instant but the coldest I have come is $30k plus my L5740 (kept in a heated garage unless it's out working) to put me in a L6060 so I watch for my asthma suffering relatives to avoid them and continue on, and my wife's learned to love the M135GX for little jobs she needs to do.