Dig down to see what’s going on in your soil

A spade, a measuring tape and a kitchen knife can help to tell you a lot about your soil. Everyone knows the problem spots in their farm – where the water lies or the crop struggles to come up, but you can’t solve that problem until you have information.

What looks like the same problem on the soil surface might look different underneath that surface.

Mark Plunkett explained at Teagasc’s recent soils masterclass that there are two ways of assessing soil structure. In grassland, farmers generally dig to 25cm or the depth of the spade.

However, on tillage farms which practice ploughing, the double-spade method is used. The plough layer is examined and then the 25cm below that layer is assessed.

Mark noted that the plough layer is generally in good shape unless something out of the ordinary happens. He added that where cover crops are grown or organic manures are applied the layer is generally in better condition than where no action is taken apart from ploughing.

Tapping the soil with a knife or trowel and finding spots of resistance can tell you a lot about compaction levels and structure.

Mark noted a few things to look out for when examining the soil:
  • Colour;
  • Rooting;
  • Size and shape of the aggregates;
  • Mottling.

When pulling out the top layer of soil from a hole dug beside a gap – where machinery had been moving – Mark showed attendees the big lumps of soil, which were compact and had no room for biological activity.

There was also poor movement of roots through the soil.

Just a few feet away where less traffic had passed by, the top layer was breaking up and roots were much more abundant and growing vertically, rather than horizontally.

Dig more than once

Cathal Somers noted that you can’t fix a car without lifting up the bonnet so in order to know what’s going on in your soil you have to dig down. In order to get a true reflection of a field then a number of digs should be carried out.

It’s also important to dig in a good and a bad area of a field. “Earthworms and roots are all good signs,” Cathal explained.

However, as he came across some red mottling he stated that this is a sign that the water cannot get down through the soil and evaporates away. The red colour comes from iron which is left behind.

If you keep mining and mining soil organic matter and never treat the soil you’re eventually going to get disastrous soil. Your production levels will be down. Everything will be down.

Cathal mentioned some woodchip and maize plastic which could be seen in the soil profile. He explained that if there was more activity in the soil these products would most likely have broken down.

The bacteria and the worms will work a lot better if there’s good movement, but if it’s packed everything is under pressure.

“If an earthworm can’t move, water is not going to move and roots are not going to move,” Cathal added.

Once your soil is assessed you can take action. This may be the application of organic manures, sowing cover crops, the use of a subsoiler or a change in tillage type or depth.

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