Persistent rainy weather meant that harvest equipment drove over many first cut alfalfa acres when the soil was wet or saturated. The impact of driving equipment on those fields is visible in terms of fewer plants and/or less vigorous regrowth. Obviously driving tractors and harvesting equipment over wet soil causes compaction that reduces yield. Another yield loss factor that alfalfa growers need to consider is the fact that wheel traffic during each harvest regardless of wet or dry soil conditions can break off alfalfa stem regrowth. Bruce Anderson, Extension Forage Specialist at the University of Nebraska, in an article entitled “Wheel Traffic Reduces Alfalfa Yield and Persistence” wrote that “when fields are dry and firm, plants driven on within one day of cutting and before regrowth occurs will yield 5 to 7 percent less at next cutting. When fields are wet, wheel traffic causes more compaction and yield loss typically exceeds 30 percent, even if regrowth has not yet started.”
Research at the University of Wisconsin by Dan Undersander, Extension Forage Agronomist, compared wheel traffic of harvest equipment at 2 days after cutting versus 5 days after cutting. Results indicated that the yield at next harvest was reduced about 6% for each day of delay in driving over the field. Yield loss resulted from regrowth stems broken by tires. Minimize yield loss from tire traffic breaking stems by removing the forage from the field as soon as possible after cutting and applying any manure or fertilizer immediately after harvest rather than waiting until regrowth has started.
Specific recommendations to minimize wheel traffic damage include harvesting high yielding alfalfa fields as a high moisture forage such as silage or baleage. Consider using larger harvest equipment to reduce the percent of field covered with wheel tracks. Avoid unnecessary trips across the field. When trips are necessary it is better to drive over the same area multiple times rather than “spreading out” trips across the field. Remember, most soil compaction occurs in that first pass.