June 20, 2006

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OVERTON – New equipment will enable Texas Agricultural Experiment Station scientists fine- tune grassland management to sequester carbon dioxide, a greenhouse gas.

The new equipment, a carbon, nitrogen, sulfur analyzer, will also allow him and other researchers at the Texas A&M University System Agricultural Research and Extension Center at Overton to more quickly analyze the nutritive value of forages, said Dr. Vincent Haby, Experiment Station soil scientist.

Carbon sequestration is an important research area because of the rising concentrations of carbon dioxide in the Earth's atmosphere. Rising carbon dioxide is now widely recognized by the scientific community to be linked to global warming.

All plants, to varying degrees, take carbon dioxide from the atmosphere, and biologically tie-up or "sequester" carbon in the soil, said Dr. Maria Silveira, Experiment Station post-doctoral associate in soil science.

Most people probably associate carbon sequestration with forests, she said.. But many don't realize that scientific authorities believe grasslands may cover 25 percent or more of the Earth's land area.

"(Grasslands) provide an important component of terrestrial carbon dioxide sequestration," Silveira said. "Unlike tropical forests, however, where the majority of the carbon is in the above-ground vegetation, the major carbon pools in grasslands are located in the soil."

In soil, carbon is sequestered two ways. One way is by a physical process: Carbon can be tied up by soil particles so that microorganisms cannot access it and release it back into the atmosphere as carbon dioxide.

The second is bio-chemical: Carbon in organic matter, such as roots, breaks down into stable compounds. Many of these compounds do not readily degrade further, and thus tie up the carbon for decades or more, Silveira said.

Variety selection and management strategies can affect how much carbon is delivered to the soil, how long it is sequestered, the size and diversity of soil microbes, and other factors, she said.

"For example, overgrazing often results in grassland degradation and decrease in carbon stocks," Silveira said. "In contrast, (the scientific literature) suggests that well-managed pasture can increase soil organic carbon by an average of 8 percent."

Experiment Station scientists at the Overton center have controlled pasture studies and are constantly evaluating new forages, Haby said. Some of these studies have been ongoing, leaving the soil undisturbed except for animal traffic, for as long as 35 years. Other studies are shorter-lived, but many present unique opportunities now that the team can analyze soil and plant samples for carbon.

For example, the team is currently seeking federal grant support to:

– Investigate how different types of cattle stocking and grazing rotation plans affect the amount and the type of carbon turnover rates in the soil.

– Study how different fertilizers affect soil carbon sequestration.

– Compare how different forage varieties and species – bermudagrass and legumes – affect carbon sequestration.

– Look at how chicken litter, which is used to fertilize pastures in Texas, affects both above-ground and soil carbon levels.

– Look at how sequestered organic carbon is protected and how the soil microbes are changed in intensively managed pastures.

The new equipment burns samples and analyzes the resulting gases. The old method, involved first dissolving the samples with sulphuric or nitric acid, and created byproducts that had to be neutralized before disposal, Haby said. The new instrument produces no hazardous byproducts whatsoever.

Also, carbon analysis could not be performed with the old methods, and sulphur analysis was so "tedious and laborious" that it was more often farmed out to other labs, he said.

Plant nitrogen content is used to estimate crude protein. Sulphur is an essential component of amino acids, the building blocks of plant proteins, Haby said.