Before we had access to fairly powerful microscopes we didn't even know soil bacteria existed much less what they did. Scientists thought decomposition and nutrient cycling were chemical processes, processes that didn't involve much biology at all.
Maybe the big problem we're facing in agriculture today is that we haven't changed our views. We still believe the biogeochemical cycles are largely chemical and are best managed with chemistry.
Even with a decent microscope soil bacteria, if visible, are only specks. To really see their form you need an electron microscope - definitely outside the budget range of the average gardener or farmer.
How is this possible? Well, a gram of clay soil actually has a surface area of 24,000 square meters. That's a lot of space for a microbe. Silt and sand would have smaller areas but still plenty of room for bacteria to roam. Here's a picture of how life might look on a couple of clay particles. Clay particles are really really tiny.
"All of the 18 essential elements used first by plants then by animals are continually recycled, thanks to the bacteria of the soil." James B. Nardi, Life in the Soil, 2007
Soil bacteria along with fungi are the primary decomposer in the soil. That means they breakdown virtually everything from your lunch to a Mac Truck. They, along with fungi, are the workhorses of the compost pile.
Nitrogen is essential for life. It is present in all amino acids which make up protein and the nucleic acids of RNA and DNA. While Nitrogen is very plentiful, about 79% of our air is made of nitrogen gas, plants can only use the nitrogen if it is fixed or combined making ammonia or NH4 or Nitrates NO3. All the nitrogen we need we get either directly or indirectly from plants. And almost all of the nitrogen plants need is provided by nitrogen fixing bacteria.
These bacteria seem almost like a hybrid of a bacteria and a fungi. They look more like fungi but their inner structure is bacterial.
These elegant microbes are responsible for decomposing tough to decompose material, fixing nitrogen in association with certain plants and for many of the most important antibiotics we use in medicine today.
Ever wonder how it all began. Some clues might be found by studying the blue-green algae or cyanobacteria. These bacteria are able to make food from air, sunshine and water and fix nitrogen. They along with other hardy bits of life - fungi, mosses and lichens - create very young soils called cryptobiotic soils.