EFFECT OF WHEEL TRAFFIC ON ALFALFA YIELD
Dan Undersander and Jim Moutray
In response to farmer concerns about the effect of wheel traffic on alfalfa yields, we began a study to look at these effects. Studies were established at the UW Arlington Research Station and ABI Research Station (Napier, IA) during the spring of 2000. Twenty alfalfa varieties/experimental lines were seeded in small plots. First cutting on all plots within a site were taken on June 18 at Napier, IA and on July 18, at Arlington, WI. Wheel traffic was applied five days after cutting by driving approximately a 100 Hp tractor across the plots covering the entire plots with both wheel tracts. This was repeated three times so that wheel traffic plots received six wheel tracks. This was an attempt to simulate driving over the field with tractor, chopper, and wagons, or tractor baler, and wagon. After first cutting, some plots were cut every 21 days and some every 35 days.
The yield reductions are shown in the table below. No yield reduction occurred on first cutting because wheel traffic was not applied until after first cutting. The yield reductions due to wheel traffic on later cuttings were astounding. Wheel traffic reduced yields to 26.9 to 87.7 percent of the plots with no wheel traffic depending on the cutting and location. The plots at Napier generally had lower yield, and therefore had smaller yield reductions, because of dryer condition most of the season. We think the yield reduction do to wheel traffic will be greater on wet soils.
|
Alfalfa yield with wheel traffic
expressed as a percent of yield with no wheel traffic |
||||||
|
Site |
Days
between cuttings |
Cut
1 |
Cut
2 |
Cut
3 |
Cut
4 |
Total |
|
Arlington, WI |
21 |
97.1 |
49.0 |
48.3 |
26.9 |
63.0 |
|
Napier, IA |
21 |
107.8 |
30.1 |
54.0 |
87.7 |
80.3 |
|
|
|
|
|
|
|
|
|
Arlington, WI |
35 |
103.8 |
80.8 |
70.9 |
. |
87.4 |
|
Napier, IA |
35 |
103.4 |
38.2 |
49.6 |
. |
68.9 |
The yield of each entry for wheel traffic compared to no wheel traffic is presented in the graphs at the end of this article. While all varieties showed some yield reduction due to wheel traffic, some entries were less affected than others. Some varieties yielded up to 0.5 t/a less with wheel traffic than similar yielding varieties without wheel traffic. Since this trait appears to be so greatly affected by environmental conditions, we feel that we need another year’s data before we release varietal information.
Yield reductions due to wheel traffic can be related to physical damage to the soil and plant. Deep soil compaction is related to axel weight and surface soil compaction is related to contact weight (weight per surface area of wheel contact with soil). Wheel compaction usually only occurs on heavier soils. Wheel traffic damage to alfalfa crowns may result in cracking or breakage of the crown which will reduce the shoots produced and may allow entry of disease. In five days, shoots will have begun to regrow and if they are broken by wheel traffic this will result in a yield reduction.
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. In retrospect, it is likely that we increased wheel damage by waiting 5 days to apply it rather than applying it sooner. To the extent that the yield loss is due to damaged regrowth, the sooner the wheel traffic occurs after cutting, the less the damage will likely be. Chopping for silage at 1 day after mowing may cause less yield reduction than baling 4 to 5 days after mowing. We will be testing this next year. We also do not know whether it is better to drive in the same tracks as much as possible to spread the wheel traffic out over the field.
What can be done? While selection for traffic tolerant varieties is going on and will improve yields of alfalfa over time, there are management practices minimizing field traffic that can likely reduce the impact of wheel traffic now. These are as follows:
1) Use small tractors when possible.
2) Avoid unnecessary trips across the field when harvesting
– Mowing and conditioning in a single operation
– Do full wagons have to be hauled the length of the field?
– If bales are dropped and collected can this be done with less driving?
–
Do not drive on alfalfa field when harvesting crop of adjacent field.
3) Consider using larger harvesting equipment (there is some question about this because while less area is affected by wheel traffic, the affected area has greater weight applied to it). This could be another benefit of contract harvesting.
4) Drive on field as soon after cutting as possible (e.g. make silage from higher yielding fields, hay from lower yielding fields).
