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Soil studies yield important findings

Do prairie burnings help the environment?

By Jeff Caldwell and Steve Watson



The annual burning of the tallgrass prairies of the Flint Hills may benefit more than just the rangeland grasses. It also could benefit the entire globe by helping reduce the level of greenhouse gases that can cause global warming, according to Charles W. Rice, professor of agronomy at Kansas State University.

Each spring, thousands of acres of tallgrass prairie are burned to clear the mulch that inhibits the growth of tall grasses. Burning may also help reduce the level of carbon dioxide in the air, according to Rice, who has conducted both long- and short-term research on the soil properties at the Konza Prairie Biological Station.

“Research is showing that prairie burning increases the conversion of harmful atmospheric carbon dioxide into beneficial stored soil organic carbon. This is a process called carbon sequestration,” Rice said.

Burning increases forage productivity, and this increases the amount of carbon dioxide absorbed by plants. Carbon dioxide is a “greenhouse gas,” which contributes to global warming. As more carbon dioxide is converted by plants into soil organic carbon, greenhouse gas levels are reduced.

“Burning is a complex issue. When you see something going up in smoke, all you can think is that carbon is being released into the atmosphere. This is true. It may even appear that the grass would be killed, but this is not true,” Rice said.

In a perennial biosystem, such as tallgrass prairie, what follows that initial release of carbon after burning may seem almost miraculous. The grass is rejuvenated and forage production is greatly increased compared to prairie that is not burned, Rice said. Greenhouse gas levels are reduced as the grass converts more carbon dioxide into organic carbon, and this helps slow down the rate of global warming.

Research at Konza shows a 5 percent increase in the amount of carbon absorbed by the soil, amounting to 200 pounds per acre per year, he said.

Much of his research takes place in the field, so plant and soil samples are indicative of the entire population. From that point, some work takes place in a laboratory, where the natural system can be simulated and manipulated to test the plant reactions to different conditions. "We divide the soil and organic matter, and look at how much carbon is tied up in microorganisms and how much is available," Rice said.

Another research method that Rice has utilized is the addition of stable isotopes of both carbon and nitrogen. This allows the researchers to find out exactly how and where carbon and nitrogen are changing in the soil and atmosphere after grassland is burned.

Burning also has an effect on the form and amount of available soil nitrogen, Rice said. "After the rangeland is burned, the soil becomes warmer. This results in an increase in the activity of soil bacteria that transform organic nitrogen into plant available forms.

This “release” of nitrogen helps the grass start growing quickly after the burning, he said.

It is the change in carbon cycling that has the most environmental significance, however. As concerns about global warming continue to grow, the increased carbon absorption capacity shown in Rice's research could become a tool to counteract the problem in the future.

"Can we manage these ecosystems and the amounts of carbon dioxide in the air? That’s the ultimate question we are trying to answer," Rice said.

June 2002