With Tier 3 diesel emission standards now in effect for large row-crop tractors, manufacturers are already working on engine designs to meet Tier 4. This next tier, to be fully phased in by 2015, calls for an even greater reduction in the amount of soot and nitrous oxide allowable in diesel exhaust. “The way I describe it is if you drove through a large city on a smoggy day with a Tier 4 engine, the air coming out of the tractor would be cleaner than the air coming in,” says Jim Wienkes, John Deere tractor engineering manager.

Getting the engine and tractor to meet the new Tier 4 rules is difficult. “If the engineering challenge to meet Tier 3 was a factor of 1, Tier 4 is going to be a factor of 3,” Wienkes says. Engineers have several methods they can use to create cleaner-burning engines, but each has its own set of trade-offs. Expect to see Tier 4 engines available on some 2009 tractors.