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.