As the winter’s snow melts across the Prairies, many western Canadian farmers are going to be disappointed to see that those deep ruts caused by last season’s wet harvest conditions are right where farmers left them in the fall. Inconvenient? Absolutely. Ugly? Yes, that too. But a big deal? In fact, ruts are much more of a problem and much longer lasting than most farmers think.
“If farmers are dealing with major ruts, they definitely do take it seriously, but I think their concern has more to do with having a good seedbed prepared for the following spring and the impact on equipment operations in the field due to the ruts,” says Marla Riekman, a soil management specialist with Manitoba Agriculture.
Instead of only considering the immediate downsides of ruts, farmers should also be aware of their long-term costs.
A tire rolling through wet ground functions a lot like a barge pushing through water. The rotation of the tire pushes a wave of soil up ahead of the tire. The tire then climbs the wave, pushing soil sideways and leaving a rut behind. While a rut, like any ground that has been run over by equipment, does have some compaction from the weight of the machinery, the bigger issue comes from the soil displacement.
“A rut is more of a smeared, deformed soil than a compacted soil,” says Jodi DeJong-Hughes, a regional extension educator with the University of Minnesota. “The loss of soil structure translates to a significant decrease in yield: right in the rut areas you’ll see about a 16–17 per cent yield hit that’ll last for about three years.”
When soil is displaced, chunks are broken into fine particles and air is squeezed out. When ruts are mechanically filled in, the additional movement causes more of the same. Though you might not be able to see ruts once they’ve been filled back in, the displaced soil’s fine texture and low air content mean it will warm more slowly, stay wet longer, support more root and seedling disease, decrease plants’ nutrient uptake and compromise water infiltration, all ultimately leading to decreased yield.
“What we see is that ruts don’t hurt overall crop population — seeds can germinate — but [plants growing in ruts] have trouble with rooting and getting going. They are one to two growth stages behind the rest of the crop. If you’re behind by one growth stage in corn, for example, that plant is considered a weed. They can absolutely be behind by that much,” says DeJong-Hughes. “Ruts also create more soil disease, because disease can really take off in cooler, wetter soil.”
It can be tempting to rip deep ruts deeper to break up the compacted rut area and smooth the surface. Resist the urge.
“Just fill them in. That’s the best you can do. You are going to have a yield hit; there’s no getting around it,” says DeJong-Hughes. “The No. 1 defence against compaction and rutting is soil structure. The more you disrupt the soil, the more you destroy its soil structure so that the next time you’re out in wet conditions, the deeper you’ll create new ruts.”
“Zero till farmers definitely have an extra challenge when it comes to cleaning up ruts,” adds Riekman. “Generally, we recommend light tillage, just deep enough to fill the ruts in, running parallel to the ruts so that they only are tilling the rutted areas.”
More importantly, producers should do all they can to minimize ruts in future. The wetter the ground, the more rutting will occur. Though producers don’t always have the option to leave a field that needs seeding or harvesting, the long-term yield cost of ruts should be considered. The 15–16 per cent yield loss over three years just might justify the inconvenience of leaving the wettest parts of the field for last, the risk of waiting an extra day or two to get into a field and/or the investment of switching to controlled traffic farming.