“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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