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Minimize Traffic Over Fields To Increase Alfalfa Yields

Driving machinery over fields can significantly reduce yields of alfalfa, one of the state”s most important crops, according to a University of Wisconsin-Madison researcher. A preliminary study at the Arlington Agricultural Research Station found that wheel traffic cut alfalfa yields by up to 70 percent for a single cutting, and the average was 30 percent, according to Dan Undersander, an extension forage specialist with the College of Agricultural and Life Sciences.

Farmers can reduce the problem by avoiding unnecessary traffic, minimizing vehicle weight, and growing traffic-tolerant alfalfa varieties, he says.

“Compaction from wheel traffic has a major effect on yields-it can equal effects from pests like the leaf hopper, and may wipe out genetic differences designed to improve yields,” he says. “We recommend that farmers consider whether or not they need to drive across their fields, and try to minimize the weight of their vehicles.”

Farmers must drive over fields to harvest a crop. However, they sometimes use heavier equipment than necessary, or drive across alfalfa fields to reach adjacent fields. This both crushes the plants and compacts the soil.

Farmers with small harvesting equipment might cover 25 to 30 percent of the field with wheel traffic during harvest. One option is to hire contract harvesters with larger equipment whose wheels would cover only 5 to 10 percent of the field. The less traffic a field gets, the better yields will be, says Undersander.

Undersander also studied whether the variety of alfalfa made a difference. “Some strains of alfalfa appear to be less affected by being driven over,” he says, “but it”s too early to make any recommendations. We need to study more varieties this summer.” He speculates that some strains may have roots that penetrate compacted soil better. Other factors may be how fast the plant grows after being cut, and how far the crown is located from the ground; lower crowns suffer less damage from wheel traffic. This summer, Undersander will also try to determine the relative yield reduction from plant damage and soil compaction in different types of soil.

However, Undersander stresses that genetics are secondary to good management practices. “The most important thing is to minimize the amount of driving over the fields,” he says. Findings from this work will be posted this summer here .