“Compaction is rele­vant in grass­land too”

Compaction is an issue that is often discussed in rela­tion to arable land – but it can also be a problem in grass­land. Olivia Cooper speaks to soil expert Philip Wright to find out more.

How much of a problem is compaction in grass­land?

Compaction is just as rele­vant in grass­land as in arable farming. Grass roots react to compaction in the same way as arable crops, and if it’s compacted grass will show it quite quickly. High stocking densi­ties can put a lot of pres­sure on soils, partic­u­larly if it’s wet when the soil is vulner­able to damage, resulting in poaching and tram­pling.

How do you iden­tify compaction in grass­land?

You will see areas where the grass is performing badly – is it lying wet or yellowing under stress? Commonly poached areas are around feeders, gate­ways and tracks, but there may also be compaction from machinery, espe­cially where pres­sures are high and concen­trated in similar areas. Look for differ­ences in grass growth.

Having iden­ti­fied problem areas, dig a hole in a good area of the field to get a feel for what the soil struc­ture should be like, and then dig in the bad areas – you’ll be able to feel and see the differ­ence straight away. But in undu­lating fields be aware that any barriers at depth will channel water to low spots, so it might not be the low spots that are actu­ally the problem. Dig a series of holes to at least 1.5-2 spade depths, and consider how hard or easy the soil is to dig. Only dig on two sides of the hole, then prise off some soil on a non-smeared face – it should break away verti­cally; if it frac­tures into hori­zontal slabs that’s an indi­ca­tion of compacted layers.

You should also look at the colour of the soil, check its smell, pres­ence of worms, and root growth.

Look at the mois­ture in the soil profile. If there is a wet layer over a dry layer, it’s clear that water isn’t getting through. You should also look at the colour of the soil, check its smell, pres­ence of worms, and root growth. Are the roots growing all the way down or reaching a layer and then stop­ping? All of this will help you iden­tify the level and depth of compaction, so you can decide how to deal with it.

How should I alle­viate grass­land compaction?

Grass roots can support and improve soil struc­ture – and dry or frosty weather can offer natural improve­ment through shrinking and cracking. There is a temp­ta­tion to go in with a deep subsoiler or plough, but that will cost more in fuel, disrupt the natural soil struc­ture and poten­tially do more damage. You need to iden­tify the limiting factor in the soil and do just enough to alle­viate it – use the metal just enough to allow the roots to do the rest of the job.

Before any mechan­ical oper­a­tions, make sure the soil isn’t too wet or it will just smear.

Before any mechan­ical oper­a­tions, make sure the soil isn’t too wet or it will just smear. If soil crum­bles when rubbing it into a ribbon it’s fine, but if you can roll it into a worm it’s too wet. For shallow compaction and poaching use a pasture aerator with angled blades to slit and lift the soil slightly. If you need to go deeper use a low surface distur­bance sward lifter to produce vertical cracks, getting air and water to the roots – even though you’ll cut a few off they’ll grow back quickly and stabilise the soil. Modern equip­ment can be set to an accu­rate depth so as not to go too deep, and has cutting discs allied to low distur­bance geom­etry lifting legs, and a rear roller to main­tain the sward.

If a ley needs reseeding and compaction is a problem, ploughing will aerate the soil and miner­alise some nitrogen to get seeds off to a good start. If the soil is wet and deeply compacted, leave it to dry out after ploughing and then go in with a subsoiler. But if you plough regu­larly, always working to the same depth can create a compacted layer, so try to alter­nate plough depth.

How impor­tant is good drainage?

Well drained pasture will extend your grazing window and make the soil less vulner­able to damage. Compaction will stop water from reaching field drains, if you have them. But it may be that your field drains are the problem – if they are blocked the field will lie wet. Check your drainage outfalls after rain to see if they’re running. It might be that your drains are in need of main­te­nance. If the soil type and topog­raphy are suit­able, you could consider putting in mole drains, but there is a danger of chan­nelling water to low spots, so get an expert to check it first.

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