Effects of transmission gear selection on tractor performance and fuel costs during deep tillage operations

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Deep tillage operations required to alleviate soil compaction common in the Southeastern US remain energy intensive and expensive. Equipment performance and in-field efficiency are two variables that can be improved to minimize fuel consumption and ultimately reduce input costs for crop production. The objective of this study was to investigate the effects of transmission gear selection on fuel costs, draft, and other equipment performance variables using two deep tillage implements. Three different transmission gears were selected which represented slow, normal, and fast operating speeds for two typical in-row, integral subsoilers (KMC generation I rip-strip and Bigham Brothers Paratill™). Tractor fuel consumption, slip, axle torque, and engine speed were measured in real-time along with transverse and vertical draft forces. Results indicated a 105% increase in fuel consumption rate, a 28% increase in implement draft, and a 255% increase in power between the slow and fast speed for the Paratill™. The KMC showed a 115% increase in fuel consumption rate, a 37% increase in implement draft, and a 283% increase in power between the slow and fast speeds. Good comparisons were found between measured and estimated, using published equations, for fuel consumption (−5.3% to 4.9%) and draft (−3.6% to 17.7%). For the Paratill™, the normal speed produced the lowest fuel cost ($ 5.10/ha) but operating at this speed reduced productivity rate from 4.55 ha/h at the fast speed down to 3.23 ha/h. Conversely, the KMC fast speed provided the lowest fuel cost ($ 5.35/ha) and highest productivity rate (4.35 ha/h) for this implement. In general, the Paratill™ provided the highest productivity and lowest fuel cost when operated at the typical speeds in the Southeastern US (around the normal to fast) mostly likely due to the lower required draft. In summary, the minimum fuel usage for each implement occurred at a different ground speed however, productivity was maximized at the fast speed with data reported useful to practitioners managing these style tillage implements.