Canola School: The compaction condundrum

Soil compaction is always going to be a hot topic following a trying harvest season.

That holds true for much of the eastern Prairies and northern U.S. states this spring. Aaron Daigh, assistant professor of Soil Physics at North Dakota State University says that the 2019 growing season started off wet in the spring, which delayed planting, therefore delaying harvest. Similarly to the Prairies, many crops were left in the field over the winter and were harvested this spring.

Delayed, wet harvests, and spring harvesting often results in a lot of ruts from grain carts, trucks, and combines. Ruts that form are an indicator of deep soil compaction, explains Daigh, which will mean yield consequences this year, and possibly many years after that — it’s a multi-year recovery.

In this episode of RealAgriculture’s Canola School, Kara Oosterhuis and Daigh talk about how that compaction can affect yields, what to do about it, and how long the effects of compaction can last.

“No matter what the crop is, if it’s a small grain, large grain, if you have deep soil compaction from wheel traffic you can anticipate probably  anywhere from on average of 15 to 20 percent yield loss for the next crop and two years that’s going to follow up afterwards,” says Daigh. With the current cost of canola production, a 15 to 20 per cent yield loss can really add up.

How long can these impacts of compaction stick around? Once the compaction initially happens, it’s going to take a couple years to recover, almost no matter what you do,” says Daigh. When you have ruts in the field it’s important to understand that the compaction extends below the depth of those ruts.

Even if you have a deep ripper that can reach down 16 to 24 inches, it’s still not a reliable method to relieve that compaction, he says. “The best way to prevent losses is to prevent the compaction occurring in the first place, rather than relying on something to remediate that compaction” Daigh says. (Story continues below video)

After those first two years, compaction consequences may lighten up, says Daigh, but even when yields recover on the years where excessive rains happen again or drought conditions occur, yields may drop again by five to seven per cent. The cost of compaction can extend for up to a decade according to Daigh. Issues are not only underneath where the rut is, but can also bulge out to the sides, which is important to remember when seeing those yield losses.

With that said, are farmers better off in the long run leaving the crop in the field rather than creating those ruts? Daigh says the decision to leave a crop out is complicated and depends on storage options, seed loss risks, wildlife feeding, the forecast, and whether or not the crop is standing.

If farmers go in with tillage to level land and smooth out ruts, compaction below tillage depth persists. As balance, it’s important not to till below the level of the rut, Daigh warns, because usually the soil down at the compacted level is wet and the situation can be made worse if you smear that compacted soil over.

Compaction can be measured with a common penetrometer —a rod with a cone on one end and a pressure gauge on the other. Measure compaction perpendicular to your plant rows to easily find where the ruts and compacted areas are. It’s an easy and efficient way to tell if the compaction is still there, after ruts have been smoothed out, Daigh says.

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