Effects of Equipment Traffic on Tillering and Yield of Winter Wheat

Chapter 7 – Plant Development, No. 3, Spring 1988

Don Wysocki

The effect of wheel traffic on wheat seedlings from herbicide application or other operations is usually considered acceptable because the benefits of the operation far exceed the damage incurred. The severity of damage inflicted by wheel traffic on seedlings depends on several factors. Among these are axle load, tire or track size and design, soil water status, stage of growth and plant size, density of traffic patterns, slope steepness and perhaps even row spacing and direction. Tire or track size and axle load can be controlled within limits by the type of spray application systems.

In 1987, STEEP researchers Don Rydrych, OSU weed scientist, and Dale Wilkins, USDA-ARS Ag engineer, compared the traffic damage that resulted from a combine sprayer, wheel tractor, swamp buggy and a ?4 ton truck sprayer. Yield and plant damage were assessed by sampling adjacent damaged and undamaged rows. Two rows were sampled for each set of wheel tracks and compared with two undamaged rows. Spraying date, trial location, stage of growth and yields for each type of system are presented in Table 1.

Yield differences between damaged and undamaged rows were substantial, irrespective of the type of vehicle. Yield differences between the various types of vehicles, however, cannot be directly compared because of differences in growth stage and soil moisture at the time of spraying.

Total yield reductions for the field were computed on the basis of one set of tracks per 48-foot boom width. Thus, the yield reduction observed in the damaged rows was apportioned over a 48-foot swath. On this basis the actual yield reductions resulting from vehicular traffic range from 1 to 2 bushels/acre and are statistically insignificant.

It was suspected that the reduction in yield resulted from fewer tillers on plants in the wheel track. To test this hypothesis, tiller density of four replicate samples from damaged and undamaged rows were examined at LaGrande, OR (Table 2). Tiller density averaged31 percent less in traffic-damaged rows.

Table 1. Wheel track damage in winter wheat from various spray systems (Rydyrch, OSU, Pendleton).

Tt could be concluded from this study that:

1. Traffic-damaged rows yield substantially less than undamaged rows.
2. On a field basis, the reduction in yield that resulted from single wheel tracks spaced at 48 feet ranged from 1 to 2 bushels/acre and was not statistically significant.
3. Wheel tracks spaced at 16 feet would supposedly produce yield reductions in the range of 5 to 10 bushels/acre. This level of damage is probably acceptable.
4. Traffic-damaged plants yield less than undamaged plants because they produce fewer tillers.
5. Soil and plant conditions at the time of spraying probably have a greater influence on the damage inflicted by wheel traffic than does the type of spray system.

The results of this study support minimizing the damage from wheel traffic on small grains. This means avoiding unnecessary traffic, using good judgment when soils are wet and exercising common sense about traffic. If heavy traffic is expected, concentrating it onto one area is advisable.

Table 2. Wheel track damage on tiller production in winter wheat at LaGrande, OR (Rydrych, OSU, Pendleton).