At this week’s National Ploughing Championships, the Irish Farmers Journal has been encouraging farmers to examine their soil health in a very simple way – by burying a pair of cotton underpants in the ground.

The underpants test is well-known around the world. Farmers get a pair of cotton underpants, dig a hole about three inches deep, leave them there for two months or so and dig them up again to see how much of the underpants are actually left.

Cotton, of course, is a carbon source and will be eaten by bugs and microbes, if they are in your soil. So, if your soil is active and healthy then the underpants should be eaten by microbes, but if it is not healthy they are less likely to be eaten.

The test, while not overly scientific, will give you confidence that decisions you are making on your farm are helping to improve your soil. Try out the test in different parts of the farm where management is different.

Carrying out the soil underpants test.

How to carry out the underpants test

You will need

  • Two pairs of cotton underpants.
  • A spade.
  • A flag or marker.

    • What to do

  • Dig down to three inches or so.
  • Put the underpants down horizontally across the area you have dug.
  • Put the soil back over the underpants.
  • Put the sod of grass or stubbles, etc, back over the soil.
  • Mark the spot with a flag or fencing pigtail.
  • Repeat the procedure in another area of the farm.
  • Come back in two months and dig them up.
  • Assess which has broken down more.

    • What management practices could you compare?

  • Grazing v silage.
  • Farmyard manure v no organic manure.
  • Organic manure v no organic manure.
  • Cover crop v overwinter stubble.
  • Perennial ryegrass v perennial ryegrass and clover.
  • Perennial ryegrass v multispecies swards.
  • Straw incorporated v baled and collected.
  • Plough v min-till/direct drill.
  • Field after a break crop v continuous cereals.

    • What will the test show?

    If the underpants have disintegrated when you dig them up, then it means that your soil is fairly active. The less decomposed they are, the less active your soil biology is.

    The underpants are made from cotton, which is a source of carbon. Soil microbes feed on carbon, so they will eat the cotton underpants. If they are in the soil in big numbers, then they will eat away at the cotton underpants.

    Soil microbes help to break down organic matter and release nutrients for crops to take up. Having a soil high in organic matter helps the soil to function better and cope with drought or wet weather. It can ultimately help to reduce artificial inputs and reduce costs on farm. Importantly, healthy soil can also store more carbon and offset greenhouse gas emissions.

    If your soil is not healthy and biologically active, then simple things like applying organic manure or chopping straw can help to increase earthworm and microbe activity.

    The idea originally came from the United States Department of Agriculture’s Natural Resource Conservation Service. Farmers across the world have tried out the challenge.

    Get involved

    We’re asking all of our Footprint Farmers to carry out the soil underpants test and it would be great to see more readers get involved. If you take the challenge send us in a picture or tag @farmersjournal and #footprintfarmers on Twitter.