Microbial inoculants are obviously not organic fertilizers, but bacteria, fungi, and protozoa play an essential role in every ecosystem.
In exchange for food from plants, they convert nitrogen from the air and minerals from the soil into forms that plants can use. They bring water to plant roots. They vastly improve the quality of the soil. They even control plant predators. Without them, there would be no life on earth.
Microorganism products are arguably more important that organic fertilizer products.
In landscapes where chemicals (pesticides or fertilizers) have been used, or where human beings have altered the soil, or where there is pollution (ie. especially cities), these useful microbes are often seriously lacking. A healthy ecosystem will have hundreds of millions of beneficial microbes in each gram of soil, but a depleted soil may have very little.
Fortunately, there are several ways in which we can bring these important microorganisms back as soil inoculants and plant inoculants. Composting has many uses, but perhaps the most important is the huge number of beneficial microorganisms that it provides. Since there never seems to be enough compost around, we now supplement with some very economical and effective inoculants.
Click on the links at right to learn more about effective microorganisms, mycorrhizal fungi, compost tea and nitrogen-fixing bacteria.