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Change the ways you burn diesel

11/06/2013 @ 1:00pm

You can’t change the price, but maybe you can change some practices and habits to reduce pressure on your diesel budget.

It’s always a good time to consider a few tactics that could shave some diesel dollars.

The price of retail diesel fuel has increased every year in the past 12 years between March and May, according to the U.S. Energy Administration (the only exceptions were 2012, 2005, and 2003). 

Looking at likely price increases, Iowa State University Extension agricultural engineer Mark Hanna and ISU Farm Energy Initiative program coordinator Dana Petersen offer some suggestions. 

Fuel prices have gone on the upswing each spring since 2005 (except in 2012). If you’re confident about what’s ahead, it may be a good strategy to buy spring diesel late this winter. 

“Before buying fuel ahead of time, look at your management strategy and see what you need,” Petersen says. “For instance, you might want to check with people who do commodity marketing to estimate where fuel prices are heading.” 

Also, it’s a good time to take a fresh look at field operations in the coming growing season. 

“It sounds trite, but leaving the equipment parked in the shed saves 100%, and it can be a good decision for some folks,” says Hanna. “Think about what the benefit is to being in the field. Is it profitable for your operation? If you can leave equipment parked in the shed, that’s a direct savings.”

According to Hanna, most farms have four approaches for reducing diesel fuel consumption: tillage operations, tractor operation, wheel slippage, and tire inflation. A fifth opportunity may be open if a tractor trade or purchase is on the planning board. 

On a typical Iowa farm, Hanna says, about half the energy bills are for diesel fuel and gasoline. If total fuel use is about 5 gallons per acre, approximately half the fuel goes into planting, spraying, and harvesting operations for corn and soybeans. The other half goes into tillage. Similarly, farms using minimum-tillage or no-till may use 2 gallons (or less) total fuel per acre. 

Carefully calculate how that tillage will affect profit, Hanna says. The deeper the tillage, the more fuel it takes. At approximately 2 to 4 inches of soil disturbance, the fuel consumed will be pretty constant. Going deeper, however, is costly. Doubling the working depth from 6 to 12 inches, for example, will nearly double the fuel consumption.  

These efforts need to be considered in light of the crop response. Will the corn or soybeans respond to the deeper soil disturbance?

“When you compare chisel plowing to deeper tillage of subsoil,” Hanna says, “we don’t find any yield difference for corn in our research plots. You need a valid reason for doing tillage, such as soil compaction.

“Here in the western Corn Belt, we don’t see soybeans responding to tillage, either,” he continues. “When we compare soybeans in a no-till system vs. a full-width tillage system over three or four years, it’s hard to see any yield advantage for the tillage side.” 

Locally, the ISU team at Ames suggests using a low-tillage system for soybeans, in preference to conventional tillage with two or three machinery passes. Cutting out a second pass may save .75 gallon per acre; eliminating a primary pass saves twice that. 

Combining two operations into one pass also can save diesel, Hanna says. A combination tool will take more diesel than a single-purpose tool, but it reduces the time pressure and eliminates one tractor pass in the field.  

Tractor operation

Review all of your options when you are considering the tractor setup for each field job. “It may come as a surprise, but it’s not uncommon in row-crop operations for your tractor to be working at 60% or 70% of its full capacity, or even less,” Hanna says. 

“For partial loads, go one or two gears higher and pull back on the throttle. That’s where a 10% savings would be pretty common for a three-quarter load. For a one-half load of maybe a sprayer operation or a light disking, you can expect about 20% fuel savings.”

Maintenance on a tractor – new or old – has a direct effect on fuel economy, Hanna says. He recalls a University of Missouri test on used tractors with a PTO dynamometer. The tractors were retested after their air and fuel filters were changed, and they got about a 4% boost in fuel economy.

“If there’s a 200-hour service life on a filter, you want to change it at least every 200 hours and maybe a little bit ahead of that. Filters do have a bit of a cost, but you can make that back pretty quickly,” Hanna says.

Wheel slippage

Traction requires a little slippage. Top fuel efficiency requires that tractor drive wheels slip slightly on the soil surface. The amount of slip that’s optimal will vary with conditions. 

Slippage should be in the range of 8% to 13% on firm soil with a heavy load on the drawbar. For tilled (softer) soil, the optimal range for fuel economy is 10% to 15% slippage. If the slippage goes higher, the tractor may not be ballasted properly or the tires are overinflated. 

The dashboard of most newer tractors will display the slippage. “See if you are in an appropriate range. If not, you want to get that operator’s manual out and look at the tractor ballast for the operation you’re doing,” he says.


Tire inflation

Tire inflation will affect wheel slip and fuel economy, but inflation may not show up on the slip indicator. Overinflated tires can waste 5% to 10% of the fuel – or even more. 

That’s not new. About 20 years ago, four Ohio farmers found they could save 5% to 15% of their diesel on fall tillage by correctly inflating their tires. A fifth farmer cut his fuel consumption by a third or more when he dropped the tire pressure to the recommended level. 

Proper tire inflation requires that you know the real load on the front axle and on the rear axle. 

“Next time you’re in town, go across the scales at the local elevator to check axle weight,” Hanna recommends. “Then, get those tires inflated properly. It’s important, and your slip indicator might not pick up that difference.” 

A good tire-inflation gauge will read low pressures accurately. It should read pressure in increments of 1 psi or less. 

Changing tractors

Part of the process for choosing a tractor for the farm – whether it’s new or used – should include thoughts about fuel economy. 

“Folks may not consider comparing tractors for fuel efficiency,” Petersen says. “We don’t have an EPA sticker to suggest fuel mileage for tractors, so it’s a good idea to read the Nebraska Tractor Test lab reports.”

If you do compare similar horsepower tractors with 10 or 15 years difference in age, she says, remember that the fuel-consumption figures need a bit of interpretation. 

Today’s engines definitely are more efficient, but they also are tasked with more performance demands that take a toll on gallons per acre. For example, instrument displays demand more power than in the past, but tractor exhaust is also cleaner. 

“Fuel efficiency may not be in your top three reasons to buy a certain tractor, but I would hope that it is in your top five to 10,” she says.  

The ISU Farm Energy Initiative website has several fact sheets on energy efficiency, including fuel consumption. To find recently updated information and farm energy management topics, go to farmenergy.exnet.iastate.edu/.