In Mississippi, researchers mixed raw sheep’s wool into soil; foxglove yields rose to 1.7–3.5 times the untreated plots over two growing seasons.

It was found that uncomposted sheep’s wool led to an increased yield of purple foxglove plants in a field experiment, with harvests reaching between 1.7 and 3.5 times the output of untreated plots. Two growing seasons were observed, and the researchers examined whether they could use wool waste to supply nutrients to high-value plants instead of discarding it.The research was published in Agronomy Journal in 2008 by Valtcho D. Zheljazkov and colleagues, who used wool waste at two application rates, 15.8 and 31.7 tonnes per hectare, alongside untreated soil for comparison. The researchers measured plant yields over the following two seasons.Wool released nutrients as it broke downSheep’s wool contains nitrogen and other elements that plants need, and unlike a soluble fertiliser, raw wool does not break down immediately after being mixed into the soil. The researchers found that some of the material was able to retain its original structure after two growing seasons and several harvests. Soil that was treated with wool had higher levels of ammonium and nitrate, which are two forms of nitrogen available to plants, and increases in nitrogen and protein concentrations in plant tissue were also recorded by the researchers, along with greater soil microbial biomass. The results suggest that wool can release nutrients over time as it undergoes decomposition, which may help supply plants across more than one harvest, although the amount that has been released depends on the material, application rate and growing conditions.The experiment focused on a high-value plantThe field trial used purple foxglove, or Digitalis purpurea, which is a plant grown for compounds used in medicines. The study mainly looked at foxglove, and whether raw wool would have the same effect on vegetables, grains or other crops remains unclear. The study also included pot experiments with other high-value plants, such as pot marigold and valerian, and those experiments found increased yields after wool or human hair waste was added to the soil. The field results, however, came from the foxglove trial.A separate study that was published in the Journal of Environmental Quality in 2005 also examined uncomposted wool and hair waste as soil amendments, and found that these materials could act as slow-release sources of nutrients and help in improving some soil chemical and biological properties. The authors also wanted to look into application rates and environmental effects, including the risk of nitrate leaching.More research is needed before general recommendationsThe researchers tested very specific amounts of wool in a particular crop, and the findings cannot automatically be applied to other soils or growing conditions. The original paper also found that high wool application rates changed the composition of soil microbial communities, while at the lower rate, the researchers did not observe the same change that is relative to untreated soil. The material's effects depended in part on how much was added.Research that was published in the Journal of Environmental Management in 2020 found that several measures of soil fertility were improved and barley grain and dry-fodder yields were increased by 50% compared with untreated plots. The experiment was conducted under its own soil and growing conditions, so it provides supporting evidence for further investigation instead of a direct comparison with the Mississippi foxglove trial.These studies, together, suggest that discarded wool could serve as a source of plant nutrients, but using it practically depends on the crop, soil, quantity applied, and environmental effects. The Mississippi experiment showed that foxglove yields increased over two growing seasons; it did not establish that raw wool can replace conventional fertilisers across agriculture.You use AI every day. Now get your AI Quotient. Take the AIQ test.