Healthy soil and sustainable growing

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Switchgrass May Mean Better Soil
By Don Comis
July 17, 2008
http://www.ars.usda.gov/is/pr/2008/080717.htm

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.