Soil is the FIRST crop...all else follows.

Great (PDF) article about soil improvement from ACRES USA. You can read many more here.

Chicken Soup for the Soil
by Jerry Brunetti

(snip)
Estimated Numbers of Common Micro-Organisms Found in Healthy Agricultural Soils
Bacteria 3,000,000 to 500,000,000 in 1 g.
Actinomycetes 1,000,000 to 20,000,000 in 1 g.
Fungi 5,000 to 1,000,000 in 1 g.
Protozoa 1,000 to 500,000 in 1 g.
Algae 1,000 to 500,000 in 1 g.
Yeasts 1,000 to 100,000 in 1 g.
Nematodes 10 to 5,000 in 1 g.