Switchgrass May Mean Better Soil

Soils with native grasses such asswitchgrass have higher levels of a key soil component called glomalin thansoils planted to non-native grasses, according to a study by theAgricultural Research Service at twolocations in Mandan, N.D.

KristineNichols, a microbiologist with theARSNorthern 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 soilprobably is.

In 2004, Nichols collected soil from under grass plots established between1987 and 2002. The amount of glomalin in the soil increased as the degree ofinterdependence between plants and the arbuscular mycorrhizal fungi increased.These fungi produce glomalin and live inside plant roots and the surroundingsoil. That interdependence is greatest in warm-season native grasses such asswitchgrass, blue grama, big bluestem and indiangrass.

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

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

The increased glomalin and underground carbon storage observed withswitchgrass 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. Sheoriginally worked with soil scientist Sara Wright, who discovered and namedglomalin in 1996. Wright has since retired.

Readmore about the research in the July 2008 issue of Agricultural Researchmagazine.

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