Another perspective comes from the Nebraska Tractor Test Lab, known as the supreme court of tractor claims. The lab, located on the campus of University of Nebraska–Lincoln, conducts performance tests to verify manufacturer claims of tractors sold in the U.S.

Roger Hoy, director of the lab, says tests of new Tier 4i-compliant tractors have not been done yet because the tractors are just being launched and testing protocols are still being developed. However, the lab did test a Tier 3 tractor equipped with SCR last year.

“You can find an SCR system on the Massey Ferguson 8600 series and Challenger MT600C series tractors,” Hoy says. “AGCO installed it in some variation for Tier 3, which greatly improved their fuel economy and gave them experience with the system.”

However, the Nebraska Test Report on the Massey Ferguson 8680 states that the “DEF rate was measured at a maximum of 3% of the diesel fuel consumption,” which is an added cost buyers must consider.

“Generally as the engine worked harder creating higher combustion temperatures, more NOx was created resulting in more DEF usage,” Hoy says. “If one assumes DEF to be the same cost as diesel, you can start to compare operating costs of this tractor with a comparable model such as the John Deere 8320R.”

Hoy says a board action is under way that would require the lab to document DEF flow rates much the same as fuel flow rates when the tractors come in for official testing.

“For us and farmers, this subject will get a lot easier for everyone when we start to have some official test data to point to,” Hoy says.

For now, he advises buyers to ask plenty of questions (see “Insider’s tip sheet”). “Both the DPF and SCR systems that we have tested or observed are in my opinion well-designed systems which are not likely to have significant effects on operating costs,” Hoy says. “However, we will probably see variations of these systems that are not so well designed that may have undesirable characteristics such as exceptionally high DEF usage or active regenerations that may require the tractor to stop what it is doing in order to regenerate.”