While conducting our research on this topic, the Early Birds have compiled this list of reputable sources if you so choose to investigate further.
https://bit.ly/2Y0DIFm ~ This paper will tell you all you need to know about how different soil textures and pH impact earthworm weight and maturation, and in turn, the population growth.
https://bit.ly/2JSctEl ~ In this research paper, the authors identify the range of soil textures that best suit earthworm survival, and is perfect for anyone researching what soil percents will best suit the earthworm population they’re surveying.
https://extension.psu.edu/earthworms ~ This article details the number of soil qualities the lives of earthworms impact. It also goes into some detail about the behaviors and biology of earthworms. It is very useful for anyone learning about earthworms and how they affect their environment.
https://bit.ly/3101ZbD ~ This article talks about many aspects of the earthworm’s life, including reproduction, impact on the ecosystem, groups, and interactions with other organisms. It is a good overview on a worm’s life and the changes that come from its actions.
http://www.arborgrow.com/earthworms.cfm ~ This article is almost identical to the one above, except it has further references that you may find useful.
http://dyckarboretum.org/tag/clay-soil/ ~ This article holds valuable knowledge about the properties of clay soil, which could be useful for your research.
https://bit.ly/2YnNkZT ~ This site is a great overview with a little more detail on worms than your average gardening site. It’s great for anyone looking to learn a little more about earthworms.
https://www.thespruce.com/understanding-and-improving-clay-soil-2539857 ~ This site includes tons of information on clay soil, its advantages, disadvantages, how to improve your clay soil, and etc.
https://www.rhs.org.uk/advice/profile?pid=620 ~ This site includes a lot of information that is similar to the site above, but also includes information on where clay soil can be found, identifications of clay soil, and more.
https://www.fs.fed.us/global/iitf/pubs/ja_iitf_2005_dechaine001%20no%20claim.pdf ~ This source is full of research findings from a test in Puerto Rico to test the relation of earthworms and leaf litter decomposition.
https://www.biology.lu.se/research/research-groups/microbial-ecology/research-projects/effect-of-environmental-factors-on-fungal-and-bacterial-growth-in-soil ~ This source explains the effects of bacteria growth and fungi on soil in very specific detail.