Published on 03/04/04

Scientist studying untold world of soil microbes

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.

Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.