Switchgrass May Mean Better Soil

Soils with native grasses such as switchgrass have higher levels of a key soil component called glomalin than soils planted to non-native grasses, according to a study by the Agricultural Research Service at two locations in Mandan, N.D.

Kristine Nichols, a microbiologist with the ARS Northern Great Plains Research Laboratory in Mandan, conducted the study. Glomalin is a sugar-protein compound that might trigger the formation of soil. The more glomalin in a given soil, the better and less erosion-prone that soil probably is.

In 2004, Nichols collected soil from under grass plots established between 1987 and 2002. The amount of glomalin in the soil increased as the degree of interdependence between plants and the arbuscular mycorrhizal fungi increased. These fungi produce glomalin and live inside plant roots and the surrounding soil. That interdependence is greatest in warm-season native grasses such as switchgrass, blue grama, big bluestem and indiangrass.

Further evidence that soils underneath native grasses are higher in glomalin came from another study on rangeland areas at Mandan and near Platte, S.D.

In an earlier study, Nichols analyzed samples from undisturbed soils with native vegetation in Maryland, Georgia and Colorado. According to her analysis, glomalin stored a large percentage of the carbon found in those soils and contributed greatly to soil fertility. On average, glomalin stored 15 percent of the soil carbon, with the highest amount—30 percent— in a Colorado soil and the lowest amount—9 percent—in a Georgia soil. These results are similar to those from other soil samples taken around the world.

The increased glomalin and underground carbon storage observed with switchgrass adds to its value as a potential source of cellulosic ethanol.

Nichols uses glomalin measurements as a quick guide to evaluate how "soil-friendly" farming or rangeland practices actually are. She originally worked with soil scientist Sara Wright, who discovered and named glomalin in 1996. Wright has since retired.

Read more about the research in the July 2008 issue of Agricultural Research magazine.

ARS is a scientific research agency of the U.S. Department of Agriculture.