While not very scientific, one way to check the organic content of your soil is to count its earthworms. Earthworms will not spend much time in soil devoid of organic material since that is the stuff they eat. No organic material--no earthworms. To check your earthworm population, dig a hole in your lawn or garden about 12 inches deep and about 12 inches across, roughly a cubic foot of soil. Do this when the soil is not bone dry but rather nicely moist. Worms move out of dry soil.
Deposit the cubic foot of soil on a newspaper and break it up to expose its worms so you can take a census. Healthy soil has at least 5 earthworms per cubic foot. Very healthy soil easily supports 25 worms per cubic foot. Soil rich in organic material (5%) can support large worm populations. Conversely, soil lacking it, lacks worms.
Counting Bacteria and other Microbes
Since a tablespoon of healthy soil can contain over 1 billion microbes, you won’t be counting bacteria the way you did with the earthworms. There are on the market a number of companies that will test you soil for its microbial population. These tests are not cheap, but the price should be coming down in the next few years so that they are more commonly available.