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3/5/2012 - 3/11/2012

Improving Diesel Fuel Efficiency for Spring Field Operations

By Mark Hanna and Dana Petersen, Department of Agricultural and Biosystems Engineering

Spring is here and, not surprisingly, diesel prices are trending upward. Taking time to implement a few simple management techniques can reduce farm fuel consumption and keep machinery running smoothly.

Even with an established tillage strategy, it may be time to review profitability potential. Once you till beyond the first 3 to 4 inches of soil in a given tillage operation, the amount of fuel used increases directly with tillage depth. Even on some colder, wetter glacial till soils on Iowa State University research farms in north central and central Iowa, corn yields have been as good or better from chisel plowing at a 6 to 8 inch depth as compared to subsoiling or ripping at depths of 12 inches or more. Three-to-five year averages from tillage plot comparisons at ISU research farms around the state generally have shown no yield differences  across systems (e.g., no-till, chisel, subsoil/rip) when soybeans were grown (PM 2089D, Limiting field operations).

Regardless of tillage management, some spring tractor operations will be required. Several techniques can help to save 5 to 15 percent or more of fuel. Consistently changing engine air and fuel filters on a timely basis, as suggested in the tractor operation manual, saves 3 to 4 percent of fuel (PM 2089L, Tractor maintenance to conserve energy). Cooling system maintenance is also important to ensure that the optimal combustion occurs.

Tractor operations required for row crops often don’t demand peak power from the tractor. When pulling lighter drawbar loads such as small tillage equipment or a planter that many be mismatched to the tractor’s power, improve fuel  efficiency by shifting the transmission to a higher gear and reducing the engine throttle setting (PM-2089M, Shift up and throttle back to save tractor fuel). Tractor tests indicate average fuel savings of 10 percent can be obtained when operating at three-fourths tractor load and approximately 20 percent savings at one-half load. Some newer, higher horsepower tractors offer the option to do this automatically through use of electronic load sensors and a continuously variable transmission.

Tractor drive wheels must slip a bit to develop optimal fuel efficiency on soil surfaces. Optimal slip varies with conditions, but for heavier drawbar loads slip should be in a range of about 8 to 13 percent on firm (untilled) soil and slightly greater, about 10 to 15 percent slip on tilled soil throughout most of Iowa. Slip is difficult to see with the naked eye at these levels, but measurement is often available from the dashboard on newer/higher horsepower tractors. If slip is outside these ranges, consult the operation manual (or PM 2089G, Ballasting tractors for fuel efficiency) for further information on proper ballasting.

Tire inflation also affects wheel slip and fuel economy. Know the correct inflation pressure for the weight the tire is carrying, use a good tire inflation gauge capable of reading lower pressures – less than 30 pound per square inch (psi) – in 2 psi increments and check pressure periodically. 

Most diesel tractors are relatively fuel efficient even at partial loads when the operator follows these tips, and shifting to a higher gear and reducing the throttle setting is particularly important for partial loads. Before purchasing a new or used tractor, it’s still a good idea to consider size requirements, including engine power, hydraulic system capacity and braking ability. Information from OECD (Nebraska) tractor tests can be used to help compare projected fuel use by tractors under consideration (PM 2089O, Fuel efficiency factors for tractor selection). 

More information on these and other farm energy management topics from ISU Farm Energy can be found at .


Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. Hanna can be reached at or (515) 294-0468. Dana Petersen is  an extension program coordinator for ISU Farm Energy. She can be reached at  or 515-294-5233.

Evaluate Forage Stands for Winter Injury

By Stephen K. Barnhart, Department of Agronomy

What an unusual winter – warmer than most; not much snow cover. Our perennial forage plants have experienced the same conditions.

Perennial forages respond to the cooling days of autumn and “cold harden” to their genetic winter hardiness limits. As long as temperatures in the crown area, or upper few inches of the soil, remain between near 0 degrees F and 35 degrees F the plants remain dormant. Snow cover and residual vegetative cover help to insulate the soil and stabilize soil and crown temperatures. Under ideal conditions, as spring temperatures warm through March, the plants break dormancy and regrow normally into the spring. Winter injury and winter kill can occur if crown temperatures go much below 0 degrees F, and when mid-winter warm spells cause the plants to break dormancy early and become more susceptible to late-winter cold crown temperatures.  Freezing of ponded water in low-laying areas frequently causes localized spots of winterkill in fields.

This winter, the crown temperatures have likely not been cold enough for direct cold injury, even without snow cover. While day temperatures have been warmer than normal through February, night temperatures have, hopefully, been cold enough to prevent the plants from breaking dormancy. How well did they handle this winter? It is time to go find out.  

Stand Evaluation
When evaluating alfalfa in late winter for winter injury, consider both the number of plants per square foot, and for alfalfa, the age of the stand. Crown and root diseases also have a major effect on stand reduction of legumes, so plants should be checked for dead, dying or diseased crown and root tissue. Winter-injured plants may survive satisfactorily, but are often slow to recover in spring, so a quick decision to destroy a winter injured stand is not recom¬mended.

  1. Wait until the spring regrowth is about three to four inches high.
  2. Select random stand count sites. Check at least one 1-square-foot site for every five to ten acres.
  3. Dig up all of the plants in the 1-square-foot area. Pick at the crown and buds with a knife to determine if the tissue is still alive. 
  4. Then count the number of live plants per square foot. Use Table 1 to begin your rating of the stand.
  5. Next, split the taproots and evaluate their general health. The core of a healthy taproot is firm and creamy-white. Damaged or dying taproots are yellowish-brown to chocolate-brown in color and watery or dry and fibrous in texture. Only healthy plants will contribute significantly to yield, so if the taproots are more than 50 percent diseased, reduce your initial stand count accordingly.

Table 1.  Age of stand and rating of winter survival

Plan your management this season, based on your stand evaluation.

  • If stands are winter-injured, but will be harvested this season, allow plants to mature to 10 to 25 percent bloom or later, before cutting.
  • Increase cutting height to three to four inches
  • Maintain good fertilizer and insect management  
  • If stands are severely winter injured, and you have incurred a significant loss to planned stored forage, plan to reestablish a new hay field this spring, and begin to plan for any needed supplemental harvested and stored forage needed until the new seeding becomes adequately productive.

Assess red clover stands similarly.    

Perennial forage grasses often survive better than winter hardy legumes. However, orchardgrass and ryegrasses are more susceptible to winter injury. Visual evaluation of grass regrowth and vitality of crown tissue is suggested when evaluating winter survival of pastures.

Reseeding in hayfields or pastures might be needed
Reseeding more alfalfa into or immediately after a 2-year old or older stand is not recommended. Overseedng or drilling grasses or red clover into thin or winter damaged stands should be done from now through April. Delaying seeding increases the risk of weed and surviving forage plant competition and seedling loss to increasingly dry and hot soil surface conditions of early summer.

Additional Iowa State University Extension and Outreach publications for further information:
Evaluation for winter injury 
Selecting forage species 
Establishing new forage stands
Interseeding and No-till renovation 

Stephen K. Barnhart is an ISU Extension forage specialist; he can be reached at

This article was published originally on 3/12/2012 The information contained within the article may or may not be up to date depending on when you are accessing the information.

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