Wheel traffic is known to increase soil compaction which, on some soils, reduces macropore air permeability, soil water infiltration and root development of alfalfa, in turn reducing yield. However, University of Wisconsin research has indicated the largest effect of wheel traffic is to break off regrowing alfalfa stems thereby reducing next cutting yield.

How much is yield of next cutting reduced?

We compared harvesting (wheel traffic) at two days after cutting versus five days after cutting. As the graph shows, the yield at the next harvest was reduced about 6% for each day’s delay in traffic application after cutting.

Yield loss was largely due to the reduction in number of stems from breakage by the tires. This is shown in the picture below where traffic was applied on the left five days after mowing but not on the right. Pictures were taken 10 days after mowing.
 

What is recommended to reduce yield loss from wheel traffic?

We believe the following management recommendations will reduce yield loss due to wheel traffic:

  • Plant traffic-tolerant varieties – see link to UW extension here for multiple trial results.
    • Wheel traffic will cause some soil compaction, and associated yield loss, for grasses but will not break of stems as occurs with alfalfa.  So yield loss will be much less for grass than for alfalfa.
  • Use small tractors when possible to reduce soil compaction.
  • Avoid unnecessary trips across the field when harvesting:
    •  Combine mowing and conditioning in a single operation.
    •  Loaded wagons/trucks should be driven off the field across as small a distance as possible.
    • If bales are dropped, collect with the least amount of driving possible and as soon as possible.
    • Do not drive on alfalfa fields when harvesting crops from adjacent fields.
  • Consider using larger harvesting equipment to reduce the percentage of field covered with wheel tracks; however, the affected area will have greater weight applied to it. This could be another benefit of contract harvesting.
  • Avoid the use of tractors with dual wheels.
  • Harvest (drive on field) as soon after cutting as possible:
    • Make silage from higher yielding fields, hay from lower yielding fields.
    • Use wide swath to allow hay or haylage to dry faster.
    • Make wrapped bales to allow harvesting of wetter hay.
    • Apply manure immediately after harvest.

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