Have you ever wondered, while you are driving through rual parts of California, why certain crops are grown in certain places and not in others?  Climate plays an enormous role:  some crops like it hot and others do not.  And water is also important, as irrigation is critical for most crops grown in our state and some need more than others.

Other than those two, the biggest factor determining whether or not a piece of land can grow crops, and what crops can be grown on it, is the soil.  There are thousands of individual soils in the world, each created over millennium by the geological forces of wind and water.  But only some of them are suitable for growing food, and only a few are considered "prime farmland". Millions of acres of the world's best soil is already covered by asphalt and concrete due to urbanization.

Farmers around the world know from experience where the good soils are, and they have passed that knowledge down through the generations.  Farming good soil doesn't guarantee prosperity, but farming bad soil tends to lead to poverty.   Any soil can be ruined by bad farming practices, but it's easier to ruin bad soil.   Improving soil is much more difficult, and the worse the soil, the harder and more costly it is. 

Back in the early 20th century, the U.S. government set out to map all the soil in the country as part of an effort to protect an irreplaceable resource.  The maps created by the Soil Conservation Service (now Nature Resources Conservation Service) have guided modern agriculture for the last 80 years to focus on growing crops in the best-suited areas while avoiding others.  They have been updated over the years and are now available online both in a web-based software version as well as PDF copies of the old county-by-county soil surveys.  As great as the modern version is, it is missing some of the important details that were included in the original documents. 

The soil classifications created by the SCS  are still valid today.  They are based primarily on the geological and chemical considerations that are the fundamentals of soil science: the types of particles that make up the soil, the pH, the minerals it contains, the material that lies underneath it, etc.  The classifications are amazingly accurate given the tools that were available to the scientists who first created them.  If the Soil Survey says that the soil on your farm will grow almond trees but not peaches, for example, only an idiot would plant peaches there -- at least for commercial purposes.

But there is an entire world in the soil that is not covered by the soil survey and its classifications:  the biological life that lives in it and often makes up a large part of its mass.  Soil ecology may be just as important as its geology and chemistry in determining which soils are good for farming, but the science is still in its infancy.

What would it take to map all the organisms that live in the world's soils?  Well, last week researchers announced that they had completed mapping the DNA of the human biome -- the 100 trillion bacteria that live inside and on the human body.  It has been known for years that this biome makes up much of the mass of our bodies.  But the researchers were, in laymen's terms, completely blown away by the number and diversity of bacteria they found, as well as their genetic complexity.   Researchers noted that their existing computer system was completely overwhelmed by the sheer amount of data involved in mapping the DNA.  It's hard to imagine, then, that enough available computing exists to map the DNA of all the world's soil microorganisms.

Like medicine, agriculture still relies heavily on techniques developed decades ago.  Antibiotics kill both bad and good bacteria both, just as most pesticides do to crop pests.   The Human Biome project hopes their data will lead to new medical technologies using our bodies' own co-inhabitants to cure and prevent diseases by identifying, isolating and breeding so-called "good" bacteria and fungi using them to keep people healthy.      

Organic farmers have been pioneers in using similar techniques to build a generally healthy soil biome.  But agricultural researchers are just beginning the science of narrowing down specific soil organisms with good potential for protecting crops from insects and diseases -- with little or no environmental downside. 

A hundred years ago, the scientists that mapped out the soils of the U.S. probably could not have imagined that they were just scratching at the surface of the potential complexity that lay under their feet -- an entire universe in a cupful of soil.