Worms! If there are many worms the soil is good. If there are no worms, the soil is bad. Worms like the organic matter and convert it into tiny weeny particles that the plants (bacteria) can absorb, they also open up the soil and create structure so it drains nicely.
they say you have to build up an entire ecosystem of life in your soil to attract the most worms.
I'm trying to find more ways of attracting them but it's hard to get specific studies that show things in a quantifiable way from the gardening community. Some say leaves on the surface attract worms, some say it's composted things, some say it's compost that hasn't completely been broken down yet. But, I have yet to see studies that show precisely the percentage of worms increased by various types of organic matter. What's the optimal approach? other than just adding more organic matter.
i'm adding as much organic matter on top as I can from a variety of sources. but, it'd be great to get some actual specifics on what's most effective.
The most effective thing for me was to find an organic matter supply that has worms. If it has worms, it will have worm eggs.
An extra thing that helped was to take some of the worm organic matter (it was a trailer full of well rotted donkey manure) and stir it into my compost heaps. My compost heaps then also got infected with worms.
Worms!