This seemingly unusual experiment based on science gives a clear visual indication of soil health at different locations across the farm, according to how much cotton has decomposed. This is important because healthier soil is better at storing carbon.

Surrey Wildlife Trust changed the farming practices at Bonhurst Farm in the autumn of 2017 to a low input, extensive grazing system. A 25 acre conventional perennial ryegrass field was oversown with a diverse mix of grasses, legumes and flowering plants. The results of the experiment revealed that the soil in this field was very active with little remaining of the cotton underpants apart from the elastic

In these fields, not only had the change in farming method increased biodiversity below the ground but also above the ground with greater plant diversity for pollinators and other invertebrates as well as increasing the habitat suitability for small mammals and farmland birds.

Dr Kate Basley, citizen science coordinator at Surrey Wildlife Trust, said:

“Soil health is so important as it underpins everything else, it’s not just good for growing food and supporting biodiversity, it’s really important for storing carbon. Soils are degraded and we need to make them much healthier.

“But it can be hard and often expensive to measure soil health. So we were looking for a simple way of measuring it when I saw the #soilyourundies project by Dr. Oliver Knox at the University of New England. Farmers across the world were getting involved in locations from California to Australia, so we tried it at Bonhurst Farm and the results were fantastic. You forget soil is a living, breathing entity and here was a snapshot of soil health represented in a pair of holey underpants."

While the textile industry has tested durability of textile strips in soil for nearly 100 years, it is only recently that farmers and scientists have used the same test to measure soil health. The simple test clearly shows the complex microbial processes of single-celled organisms like bacteria and fungi at work, which use cotton as their carbon source.

When Surrey Wildlife Trust took over the management of Bonhurst Farm, near Guildford, it changed the way the farmland had been managed there for years. Conventional farming practices meant fields were ploughed, cultivated and re-sown with a single grass and clover mix every 5 years with inorganic fertiliser being applied annually to produce a high yield. Where the underpants were buried in these areas the indicators for soil health were not so good, the underpants were soiled but not eaten away.

The new method of farming at Bonhurst Farm used for cattle grazing follows agro ecological principles and focuses on enhancing soil health through diversity of root structures, increased organic matter, alleviating compaction and retaining moisture. It also reduces the dependence on chemical intervention at all stages of the farming cycle and providing a more diverse, nutrient rich diet for the cattle, which means cattle no longer need worming.

Kate Basley added: “Soiling your underpants can be tried at home in your garden too. The optimum time is during the summer months between June and August when the soil biology is more active. To nurture healthier soil avoid using pesticides and chemicals, minimise digging to avoid disturbing the complex soil life and add compost and other bulky organic materials, which not only add nutrients, but help create good soil structure.”

To conduct your own soil health test at home:

Bury some white, 100% cotton underpants in the ground four-six inches deep as the soil at that depth is most active. Good spots in the garden are flower beds because they have good moisture content.

Bury the pants so the elastic waistband is showing or mark the spot with a flag. Leave for two months then return and see what is remaining.