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The links between compaction, tire pressure, and soil texture

By: Lara de Moissac

April 29, 2021

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One concern this spring is whether or not there’s enough moisture to get a crop going, but another common springtime concern is that of compaction. Compaction is a risk every time you drive on a field, but the severity of compaction depends on where soil moisture is in the soil profile.

“You can’t compact a soil if it’s actually got enough strength to withstand that pressure that’s been put on it,” says Marla Riekman, soil management specialist at Manitoba Agriculture and Resource Development, in a recent RealAg LIVE. “It’s when your soil is moist down below that that pressure can actually allow those soil particles to push against each other.”

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If you’re dealing with a risky situation — when there’s moisture and when the big pore spaces in soil will collapse — you want to focus on having your tractor performing optimally, says Riekman. Using duals and the appropriate tire pressure (which is quite a bit lower than for road speed) allows the tire to stretch out width-wise and length-wise, spreading the pressure down over a larger area.

“If your duals are run at their rated pressure they should be compacting no more than a track would,” says Riekman. Keeping axel loads as low as possible can mitigate compaction too, adds Riekman.

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Deeper compaction that happens with the weight of equipment drives compaction deep into the soil profile, and long-term, 10 to 15 years down the road, that compaction will not come out, says Riekman. Research suggests a 10 per cent yield loss in areas with deep compaction.

Riekman suggests parking the tractor on a flat concrete pad, and if you can stick a fingernail underneath the edge of tread, you need to let air out (with the caveat that she is by no means an ag engineer).

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But how does soil texture play into compaction?

Soil texture is made up of the percentages of sand, silt, and clay (remember that texture triangle). Soil structure is the arrangement of those sand, silt, or clay particles that become a unit called an aggregate. There are networks of aggregates with pore spaces between, that get formed over time with plant root growth, animal burrowing, or human activity. Texture and the aggregate network affects the size of pore spaces for water and air infiltration.

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“Clay soils typically have a better ability to compress or compact,” says Riekman. “This is due to a couple of reasons. When you think of clay particles when wet, they can slide around more. Clay soils already have the small pore spaces there, but it’s the large pore spaces that are crushed when compaction happens.”

The large pore spaces are also where water would flow in a clay soil, so once they’re gone, the water can’t filter through the soil properly.

Sandier soils, on the other hand, don’t have the ability to shrink and swell like a clay soil does, so a sandier soil can’t crack naturally and alleviate compaction. The first time that Riekman recommended subsoiling to help with compaction was in a sandier soil.

Related:

Watch the full conversation with Riekman and RealAg LIVE host Kara Oosterhuis here!