Lower air pressure in tires to reduce soil compaction

There are no easy solutions to soil compaction 
but there are some strategies to help avoid it

Photo: File

For producers soil compaction probably feels like an unwinnable catch-22.

They need to get out and perform field operations to grow crops, but each pass contributes to the creation of soil compaction that can seriously hinder productivity. Provincial land management specialist Marla Riekman told producers at the recent St. Jean Baptist Farm Days that there are no easy answers for this challenge.

“I have to admit soil compaction is one of my most hated topics to discuss with farmers,” she said. “Because I don’t have a lot of great solutions… but there are some things you can control.”

That includes keep tires aired down and being aware of axle loads.

“We do have a lot of human-induced compaction and that is where we have excessive or untimely tillage, and things like wheel traffic and axle load are the main contributors to it,” Riekman said. “So the topic here is really, how much you can control, because there is a lot here you can’t control.”

Shallow compaction, which occurs in the first six to eight inches of soil, is caused by wheel traffic and can be reduced by lowering tire pressure, she said, noting a tire at 10 psi will have an actual force between 11 and 12 psi when in contact with the soil.

“So we need to remember that tire inflation is really important and that road speed is going to be two to three times higher than what you would need for trafficking in a field,” Riekman said. “I know that we don’t often think about checking our tire pressure and adjusting tire pressure for field conditions, but we do need to start thinking about that.”

The lowest psi recommended for any particular tire is the appropriate psi for field traffic, she said.

But deep compaction can also be a serious issue, even though it occurs three to four feet below the soil surface.

“Deep compaction is something we don’t often talk about and deep compaction is related to axle load,” said Riekman. “If you think about what axle loads are now, compared to what we used to have, they are growing.”

She noted that many producers took grain trucks off their fields to reduce the compaction caused by their narrow tires, but then replaced them with ever-larger grain carts.

“And the bigger and heavier these grain carts are becoming, the more deep compaction may end up happening in those fields,” she said. “So it’s something to think about.”

While experts suggest not running carts over the field while full, Riekman said even avoiding running full carts over the field presents its own challenges.

But the effects of compaction are real, including suppressed root growth and lower yields.

“You’re also going to have decreased water movement, because now you don’t have that pore space for water to move through,” she said. “So how does the soil compact? Well it’s simple, there is air spaces in soil, there are spaces that have water and there are spaces that have air, when the soil is crushed all the spaces that have air are crushed down.”

Conversely, a little bit of compaction in a dry year can actually increase yield by helping soil hold more moisture, although reduced air pockets also make it more difficult for roots to access nutrients like potassium.

“So what can I do to fix this? If we caused the problem using iron, through tillage, or if it was travelling over the field, or heavy axle load, can we fix the problem by using more iron?” asked Riekman.

Deep tillage can be an option, don’t just dig the shanks of a subsoiler down as deep as possible and head across the field. Instead determine the depth of the compaction and till one inch below that measurement.

“To me that is just wasting fuel. You want to go just under it and skim it and see if you can break that up, because if you just start sinking, what happens is you cause a problem deeper and you can’t go any deeper than that,” Riekman said, adding the timing of such tillage is also crucial.

“If you’re going to be subsoiling you need your soil to be dry,” she said, adding that usually means working it in the fall, but also making sure the soil isn’t so dry that there is soil loss.

Another factor farmers must consider is the cost of subsoiling, which may or may not prove effective.

“It’s a very expensive practice,” said Riekman, noting some studies put the chance of a farmer recouping the cost through increased yield at about 50 per cent.

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