Farm Ireland

Friday 20 July 2018

It's time to take stock of soil structure

Soils must be sufficiently dried out before attempting to loosen any compaction from livestock

The weight of modern machinery takes its toll on soil structure
The weight of modern machinery takes its toll on soil structure
An aerator is a useful tool - provided the problem isn't too deep in the soil

Farmers looking to rejuvenate battered permanent pasture and leys that have been subjected to continual livestock trampling and heavy machinery over the past 12 months should wait until soils have dried out sufficiently before attempting to loosen compaction. That's the message coming from specialist Richard Hales from grassland subsoiler manufacturer Sumo.

The advice is backed by independent soil management adviser Philip Wright. "Subsoiling with an implement which fractures the soil to improve drainage and rooting, whilst at the same time leaving the surface relatively undisturbed, requires the soil to be dry enough to do the job properly," suggests Mr Hales.

"The late summer/early autumn period is a good time, especially after a dry week of weather and when silage or harvest has been finished."

He stresses that this applies particularly to clay soils, where hasty use of a subsoiler may aid immediate surface water movement but is likely to only exacerbate sub-surface problems.

"The likelihood is that any action immediately after heavy rain, even if it's just an attempt to encourage the drainage of surface water, will do more damage than good by smearing and compressing the subsoil rather than fracturing it. It is better to hold off subsoiling until soils start to dry out because it is then that subsoiling will create the desired shattering effect that aids drainage and rooting."

Mr Wright, whose consultancy frequently advises tillage farmers with soil structure problems, says many of the same management tips he gives for cropping land management also apply to grassland.

The effects of compaction and poor drainage in long-term pasture have been particularly evident this year, he says, while many leys still down following last year's silage or grazing will have suffered from compaction created by machinery or livestock.

"A spade is just as important to good grassland management - whether leys or permanent pasture - as it is to the assessment of tillage soils," says Mr Wright.

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"Digging some inspection holes in problem areas is essential to help identify what problems lie underneath the surface, where the compaction layer is and how 'plastic' any sub-surface clay is.

"While on some land it may be possible after a few dry days to pull a grassland subsoiler leg through pasture or ley ground without too much surface disturbance, on clay ground in particular the high water soil contents will create high soil plasticity.

"This means the point will simply smear an impenetrable channel through the clay, compounding the drainage problem while creating very little shattering."

Generally, waterlogged soils are the result either of an impervious layer restricting movement down to the drains, or of the drains themselves being blocked, he suggests.

Either way, pulling a loosening tine through 'plastic' soil will cut a slot and smear the edges.

"While the slot may temporarily cut through the impervious layer and allow some surface water through to drier soil below, this ultimately is not solving the problem of fissuring and loosening the layer, allowing roots to penetrate and hold it open. Such a smeared slot can easily seal back over time or when the damp soil is subsequently trafficked.

"A better way of improving surface water movement in the interim will be to ensure field drains and ditches are clear and running. A good grassland subsoiler is the right tool for improving grassland drainage and rooting, but it needs to be used at the right time."

What are the other options?

If the problem is found around 15 inches below the surface, a good subsoiler is the best tool for the job.

An aerator will be of little use for a problem this deep, because the spikes on an aerator tend to be only about six inches - only about the length of a pen.

But that doesn't undermine the value of a good aerator, which can be ideal for solving a compaction problem where the issue can be closer to the surface, such as poaching by cattle. In such a scenario going in with a big subsoiler will do more harm than good. That's why it's really important to identify the depth of the problem first and choose a solution based on this.

Many farmers also tend to overlook the simple, non-mechanical management tools that they can use to manage compaction and drainage problems. For example, checking watercourse outlets and maintaining a regular drainage programme can boost your chances of avoiding waterlogged fields. Likewise, a consistent fertiliser and, particularly, lime application programme will help to keep soil pH right. Lime is often looked at as being a once every ten years job, when in reality farmers need to be much more regular with their soil testing and lime application to keep pH at a level that will improve soil structure and make nutrients available for growth.

Grazing management is the other obvious one for grassland farmers. Taking cattle off ground at the right time can prevent a lot of problems later on, but with many farmers working off farm during the day the damage can often be done before they get a chance to get cattle off wet fields. Finally, increasing soil organic matter content is key because organic matter helps both drainage and fertiliser availability. Most tillage farms have a soil organic matter content of around 6-7pc, and this can be improved by practices such as chopping in straw, growing a break crop or putting land back into grass for a few years.

* Identify the compaction depth

*l Check watercourse outlets for blockages

* Take regular soil samples at different times of the year

* Use an aerator for surface compaction

* Use a subsoiler for deeper compaction

*l Ploughing and cropping/reseeding

* Drainage

* Regular lime programme

* Use break crops to improve structure

* Stitch in grass

* Correct tyre selection

* Drain maintenance

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