Humus is not just soil, it is a community of living things. Organic matter is a breeding ground for many types of microbes, including bacteria and fungi which break down plant material, and for other microorganisms that help plants roots absorb necessary nutrients.
I agree with your analysis, but I disagree that cagers refers to an entire class of persons, all motor vehicle drivers. To me, and maybe I am not using the right definition, a cager is an @sshole motor vehicle driver.
1 Thruxton handlebars, a type of motorcycle handlebar that is shaped to provide a clip-on-type handlebar position, but which clamps on top of the yoke rather than onto the fork stanchions. 2  Thruxton handlebars are also known as  Ace 'bars  or Clubman 'bars.