Weeds as indicators of soil conditions

Has anybody got a lot of info on what a given type of weed can tell you about your soil? For example, I have one raised bed with a thick patch of Canada Thistle that butts up against a thick patch of Yellow Nutsedge. What conclusions (if any) can I draw from this, other than the possibility that thistle-loving birds crapped in one area and nutsedge lovers crapped in the other?

Different plants grow in different soil conditions. When my hard drive crashed I lost a lot of sites and one of them was all about weed indicators. :( Canada Thistle will grow just about anywhere there is disturbed soil.

Sonny

Johnston grass will grow in any soil good or bad. lol

Pirate, as you worked that bed, you probably would assume that all the soil should be pretty much the same. I don't think there could be so much difference that would cause the two plants. I think it started with two different birds crapping once each, and just went from there.

I have read that lambsquarter will indicate low N ( I think) by showing some coloring in the leaves or stem tips.

I read an article once from a person who cured a big patch of Canada thistle , leading the writer to coclude that improving the soil with organics matter made it less hospitable to the thisltle there