Correcting soil compaction

Correcting compaction can be done all-year-round: the best time to aerate is whenever ground conditions allow and you have the time!

Unfortunately, many grassland managers are put off subsoiling, or aerating because they believe the window of opportunity is so small.

“Clearly, using the wrong machine in the wrong conditions causes problems – heavy clay, for instance, will smear in very wet conditions. But if the window is too narrow, you’ve got the wrong aerator because aeration is OK at any time of year, as long as ground conditions allow,” says soil specialist Mark Tripney of isoils.

He points out that cheaper, lightweight aerators on the market can’t penetrate compacted, or very dry soils and have to travel slowly or else they flick stones. The best models are heavier, roller-type aerators which puncture holes in the top 10–15 cm (4–6”) of soil, achieving good penetration. Too many people get hung up about machine spec, or superficial surface damage, he says, and the result is that they do nothing – which is far worse.

“Grassland productivity will be more limited by soil compaction* than any perceived surface disturbance. There are no overnight miracles from aeration, but results can be seen (depending on soil temperature) at the bottom of slits within 10 days, as grass roots grow down searching for air and water. You won’t see a visible 15% lift in grass yield as a result – it needs to be measured with a plate meter.” 

While our research has shown that compaction naturally resolves if cow, or tractor, traffic is reduced, mechanical intervention is needed in severe cases, and to restore pasture productivity quickly.

However, Mark stresses that it needs to be done together with good soil analysis as chemical imbalances can also cause compaction. “Magnesium in particular is very hydroscopic and binds water to create a hard, sticky soil, whereas K and Na disperse soil particles causing it to cap,” he explains. “Don’t guess that you have compaction: dig 3–4 holes across a field (as you would take soil samples) and work out whether compaction is in the top 10–15 cm (4–6”) or down at 20–25 cm (8-10”).