To drive or not to drive? Wheel traffic and alfalfa yields

By Steve Murty, Vita Plus forage products specialist

In our pursuit for greater alfalfa yield per acre, we created a situation of loss.  What I mean is our alfalfa variety selection process has pushed farmers to select higher fall-dormancy-scored alfalfas that recover more quickly after cuttings, stay vegetative longer into the fall, and green-up more quickly in the spring.  This is accomplished through plant breeding and selection for plants that exhibit faster regrowth.  These varieties possess the desired production traits for higher yields per acre and exhibit crowns that are not as deeply set into the soil.

The quick regrowth collapses the window of time a farmer must cut, cure and remove the alfalfa crop.  Ideally, in the Upper Midwest, these fall dormancy 4 and 5 alfalfa varieties work best in a haylage system that allows the forage to be removed from the field at higher moistures in a shorter period.  The harvest equipment used in this system can increase soil compaction deep in the soil profile due to heavier axle loads, which can damage the plant and reduce subsequent yields.

Several Midwest universities have conducted multi-year research studies to create a data set showing yield loss related to wheel traffic and soil compaction.  Two studies were completed in the early 2000s to assess the effects of wheel traffic on alfalfa yields over a three-year period.  The first study found most alfalfa varieties experience some degree of yield reduction due to wheel traffic.  The second study established test plots in multiple states and looked at yield results with no wheel traffic after cutting, wheel traffic two days after cutting, and wheel traffic five days after cutting.  This study confirmed the previous results and showed wheel traffic after two days caused significantly lower yield reductions compared to five days.  You can read the full study here.

Additional varietal studies have been done to compare wheel traffic from the early research trials.  This study showed wheel traffic that occurred up to five days after cutting (dry baled hay system) lost as much as 1.5 tons per acre per year compared to non-traffic plots.

This yield reduction is due to destruction or termination of developing shoots, putting additional stress on the plant crowns and root system.  Broken crowns offer an entry point for diseases and pathogens.  The soil moisture and clay content of the soil also affect the amount of damage the alfalfa plants sustain.  Soil moisture profiles at peak moisture capacity will compact easier than soils at excessive moisture fill.  The decision to remove rain damaged forage prior to ideal soil moisture levels can have long-term negative effects on your yield potential each year.

To help avoid yield loss due to wheel traffic, try employing some of these management strategies, if possible:

• Combine trips to reduce wheel compaction.
• Mow and condition the crop in a combination application.
• Utilize lower horsepower tractors when possible to reduce axle loads.
• Add larger tires or tracks to tractors or carts used to remove the forage.
• Once wagons and trucks have been loaded, follow controlled traffic plans to reduce the number of plants damaged due to higher axle loads.
• Hire a custom harvester to perform the process utilizing larger cutters.