By Brad Haire
University of Georgia
Whether you’re in a rural field or in a city garden, pick up a
handful of soil. Inside your hand could be as many living
organisms as there are people on the earth. One gram of soil
could have several billion bacteria. It could contain as many as
5,000 kinds of organisms.
“Soil microorganisms constitute the largest single undescribed
source of genetic richness and diversity on the planet,” said
Mark Williams, a soil microbiologist with the University of
Georgia College of Agricultural and Environmental Sciences.
Micro respect
These microbes are the unsung heroes of a healthy environment,
Williams said. He’s trying to find out more about how and why
they do what they do when exposed to stresses like when soil
becomes dry.
Soil microorganisms include nematodes, protozoa and algae. Most
soil microorganisms, he said, fall under three categories:
fungi, actinomycetes and bacteria.
In most cases, microorganisms account for as much as 95 percent
of the total weight of organisms in soil, although the other
ones, including worms and insects, are the only ones you see.
Studying, identifying, numbering and comparing species of
microorganisms you can’t see with the naked eye, Williams said,
can be tough.
He uses nuclear magnetic resonance spectroscopy. It’s better
known by its medical name: magnetic resonance imaging, or MRI.
He uses some DNA-based methods and isotope analysis, too, to
study his tiny subjects.
In recent decades, the need for sustainable agricultural
practices has grown. This basically means giving as much back to
the environment as you take from it to grow a crop or raise
livestock. It includes reducing and more precisely using farm
chemicals and fertilizers in soil.
But to do this, Williams said, you have to understand
microorganisms, the primary agents that supply nutrients to
crops.
Microorganisms do mainly three things:
* Clean up the world by decomposing plant litter such as dead
roots, leaves and sticks.
* Release and make available basic plant nutrients like
nitrogen, phosphorus and sulfur.
* Make it easier for water to get into the soil and for plant
roots to penetrate and grow.
They can catch nutrients from the atmosphere, too, and break
down some pollution like sewage and chemical spills.
Wet or dry
Williams looks at how a soil’s environment can determine what
kind of and how many microorganisms are in it. He also wants to
know how they can affect and change the soil environment around
them.
His recent studies focus on how soil microbial communities
respond to wet and dry soils. This is vital to agriculture in
Georgia, he said, where a growing season can have extended
periods of either wet or dry conditions.
Knowing how microorganisms act or don’t act at different levels
of soil moisture, from drought to extreme rain, can help
scientists and farmers get the most out of the chemicals and
fertilizers they put on crops.
