Yield Implications for Driving on Alfalfa Fields

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

Driving over alfalfa fields is a necessary activity if the crop is to be harvested. Nevertheless, common sense would tell us that the potential for damage may be occurring under the wheel track in the form of plant breakage or soil compaction. Recent studies in Wisconsin and other states have tried to quantify this damage, with some interesting results. The studies were conducted by driving a 5 ton tractor across alfalfa plots and covering the entire plot with both wheel tracks.

Variety effects

Initial studies done for three years at the Arlington Research Station compared the effects of no wheel traffic versus wheel traffic two days after cutting. The yield effect (summed over 3 years) is presented in Figure 1. Note that there is extreme variation between varieties and that some yielded up to 1 ton/acre less as a result of the wheel traffic.

Figure 1

Wheel Traffic Timing

Most of the yield effect from wheel traffic is attributed to stem breakage of the new regrowth. It thus makes sense that the longer the period of time between cutting and wheel traffic, the more damage may occur. In fact, this was the case in a multiple state study looking at the yield reduction caused by wheel traffic 2 or 5 days after cutting (Table 1).

Table 1. Percent alfalfa yield reduction from wheel traffic either 2 or 5 days after cutting.

		Avg. Yield Reduction (%)
State	Seeding Yr.	2-days post-cut	5-days Post-cut
Iowa	2000		30
	2001		22

Wisconsin	2000		9
	2001	2	9

Minnesota	2001	11	29

New York	2001	3	25

Nebraska	2001	0	0

Oklahoma	2002		9

The data offers strong evidence that wheel traffic 5 days after cutting has the potential to significantly impact overall yields (reductions of 0 to 30 percent across state trials). This points to the importance of both reducing the amount of wheel traffic, limiting the area impacted by wheel traffic, and accomplishing field operations as quickly as possible after harvest.

Of course much of this is easier said than done, but there are management practices that can help in this regard. These include:

1) Variety selection – more evaluation is made to document differences. This is being done both at the university and company levels.

2) Manage equipment size – many times this can’t be controlled, but the premise is to simply use a smaller/lighter tractor if it can get the job done efficiently.

3) Avoid unnecessary trips across the field to minimize the area impacted by wheel traffic. For example, drive in the same wheel tracks with loads entering and leaving fields. Load and unload dump wagons at the end of fields rather than in the middle.

4) No dual wheels

5) Accomplish field operations as soon as possible after cutting.

6) One more good reason not to spread manure on established alfalfa.

For more information contact Mike Rankin