Uncomposted sheep’s wool led to the increased yield of purple foxglove plants in a field experiment | Wikimedia Commons
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. 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. 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 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. 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 researchers measured plant yields over the following two seasons. The experiment focused on a high-value plant The 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. The authors also wanted to look into application rates and environmental effects, including the risk of nitrate leaching.
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.