Reducing Compaction in Alfalfa Fields

Research has shown that wheel traffic can impact alfalfa yield by as much as 25 to 30%.

By Tharran Gaines

“Forty years ago, back before we even had hay conditioners on windrowers, it could be six or seven days between the time we cut the crop and we got the bales off the field, even though it might be 110 degrees in the shade,” recalls Stan Azevedo, who manages about 4,000 acres of hay and forage crops near Hanford, California. “All the while, that hay was still growing,” he adds. “And you could see the damage from the wheel tracks on the next cutting.”

25% Yield Loss

According to research in both California and Wisconsin, Azevedo’s early experience isn’t unusual. Fact is, such damage can easily reduce alfalfa yield by 25% or more. Dan Undersander, Extension forage agronomist at the University of Wisconsin, Madison, insists, “Yield reduction occurs in part due to wheel traffic that causes both deep soil compaction and surface soil compaction. However, the major damage and cause of yield loss for alfalfa harvested more than two days after cutting is due to breaking shoots that have begun to regrow.

“The amount of wheel traffic yield reduction is likely going to vary from field to field and cutting to cutting, depending on plant and soil conditions,” he continues. “However, yield loss at the next cutting becomes greater as time passes between mowing and the occurrence of traffic.”

Hesston® by Massey Ferguson WR9770 windrower.

Hesston® by Massey Ferguson WR9770 windrower.

Undersander says yield loss has generally been 4 to 6% per day for each day after mowing; hence, the yield loss of 20 to 30% when traffic occurs five days after mowing.

Reduce Traffic, Reduce Losses

Fortunately, Azevedo has discovered at least one solution since those early days of hay-making. Approximately seven years ago, he purchased a Hesston® Model 9260 windrower equipped with a Model 9070 header, which was one of the first with the optional TwinMax™ Advanced Conditioner. Today, all three of his windrowers, including the newest Hesston by Massey Ferguson® WR9770, are equipped with the TwinMax header.

“Now, with these new rotary headers and double conditioners, there are about three months in the summer when we can get the hay baled and off the field in three days,” Azevedo says. “Of course, the faster you get the hay off, the less regrowth you have that can be damaged when you drive over it.”

Dan Putnam, alfalfa and forage Extension agronomist, Department of Plant Science, University of California, Davis, agrees, “It only stands to reason that reducing the amount of traffic will reduce the amount of damage done by traffic. Traffic occurring at cutting or within a few days is less damaging to alfalfa shoots than traffic during the later harvest operations.

“Compaction due to the multiple trips is a factor, but breaking shoots that may have started to grow for the second time after cutting, has a depleting effect on stored root carbohydrates,” he adds.

That’s part of the reason Azevedo’s brother-in-law, Mark Rosa, uses an accumulator with his Hesston by Massey Ferguson Model 2170 big square baler. Because he hires somebody to pick up and stack the bales, Rosa says he typically collects and drops bales within 100 yards of each end of the field. He also drops them in a line, instead of side-by-side, so the bale loader doesn’t have to back up and run over the crop a second time.

“Not only does he save time and fuel picking up the bales, but he doesn’t have to go as far into the field to pick them up,” says Rosa, who does custom baling within an eight-mile radius of his home near Laton, California. “If it’s already been four or five days since I cut the crop and he’s running a day or two behind, it could be six days before the bales are picked up. As a result, you can generally see the tracks where he went.”

The situation gets even worse when the landowner gets in a hurry to start irrigating the field again, Rosa adds, noting that he prefers to wait a week before restarting the system. “Here in the valley, it can be anywhere from 95 to 110 degrees in the middle of summer,” he relates. “So when you put water on a field that already has traffic damage, it collects in those wheel tracks and kills the hay. Between the broken crowns, the heat and then water standing on them, the plants don’t have a chance. It’ll cook ‘em.”

Additional Solutions

Dean Morrell, AGCO product marketing manager for hay and forage equipment, says that even if a customer doesn’t have a bale accumulator or TwinMax windrower header, there are things he can do to reduce wheel traffic damage.

“Anything you can do to speed up drying time and reduce the amount of time between mowing and bale removal will certainly help reduce crop damage,” Morrell says. “That may involve spreading hay into a swath with the windrower or mower conditioner for faster drying or using one of our TD Series tedders, in some areas, to spread the crop and reduce drying time.”

Using a smaller tractor to rake two windrows together can also reduce the number of trips that a larger tractor and baler have to make over the field. Plus, it can reduce baling time substantially, especially in light crops.

“Even if a producer reduces drying time by one day, it can mean a significant reduction in crop damage.” Morrell continues. “In the meantime, we continue to look at the issue of compaction when it comes to equipment design. The use of turf tires on balers and windrowers for a larger footprint and less crop damage is one example,” he concludes. “But even features like independent header flotation on our WR Series windrowers help reduce field compaction.”

Steps to Reduce Field Compaction and Regrowth Damage

• Plant alfalfa varieties that are more tolerant of wheel traffic.

• Use a small tractor when possible (to reduce soil compaction).

• Conversely, consider using larger equipment in larger fields. While the soil on which the tractor is driven will experience a greater likelihood of compaction, larger equipment will allow for less traffic lanes in a given field and, therefore, less of the field will be compacted.

• Drive over the field as soon after cutting as possible.

• Raking at 24 hours causes less damage than raking at 48 hours.

• Merge swaths into large windrows so harvesting equipment has less driving on the field.

• Making haylage at one to two days after cutting causes less yield loss than making haylage at three to five days after cutting.

• Avoid unnecessary trips across the field when harvesting.

• Get full wagons/trucks off the field with as little driving as possible.

• If bales are dropped and collected, can it be done with less driving?

• Do not drive on an alfalfa field when harvesting crops from an adjacent field.

• Using duals on harvesting machinery is not recommended unless necessary to avoid ruts.

• Stay off wet fields. When soil moisture in the top three to six inches is near field capacity, the potential for soil compaction increases as clay content increases and soil organic matter decreases.

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