What was done
Working at the Kessler Farm Field Laboratory in McClain County, Oklahoma, "in a long-term field experiment," according to the authors, they "explored how annual clipping for biofuel feedstock production and warming caused soil erosion and accompanying carbon and nitrogen losses in tallgrass prairie," where warming was provided by infrared heaters suspended 1.5 m above the ground, as described by Kimball (2005), leading to air temperatures being raised by an average of 1.47°C and soil temperatures in the clipping plots by 1.98°C.

What was learned
The results of this eye-opening experiment revealed that the average relative depth of erosion caused by clipping was 1.65 and 0.54 mm/year, respectively, in the warmed and control plots from November 21, 1999 to April 21, 2009, that the soil erosion rate was 2148 g/m²/year in the warmed plots and 693 g/m²/year in the control plots, that soil organic carbon was lost at a rate of 69.6 g/m²/year in the warmed plots and 22.5 g/m²/year in the control plots, and that total nitrogen was lost at a rate of 4.6 g/m²/year in the warmed plots and 1.4 g/m²/year in the control plots. And Xue et al. make a point of noting, in this regard, that "the amount of carbon and nitrogen loss caused by clipping is equivalent to, or even larger than, changes caused by global change factors."

What it means
In discussing their findings, the five researchers say their results suggest that "clipping for biofuel harvest results in significant soil erosion and accompanying losses of soil carbon and nitrogen, which is aggravated by warming." And they indicate that "soil erosion is one of the most pressing global environmental challenges facing the world today, causing declining soil productivity and crop yields, which may cause difficulties in meeting the rising demand for food and energy (Brink et al., 1977; Brown, 1981, Lal, 2004; MEA, 2005)," which facts lead one to wonder if the biofuel "cure" for the global warming "disease" might not be worse than the malady itself.

References
Brink, R.A., Densmore, J.W. and Hill, G.A. 1977. Soil deterioration and the growing world demand for food. Science 197: 625-630.

Brown, L.R. 1981. World population growth, soil erosion, and food security. Science 214: 995-1002.

Kimball, B.A. 2005. Theory and performance of an infrared heater for ecosystem warming. Global Change Biology 11: 2041-2056.

Lal, R. 2004. Soil carbon sequestration impacts on global climate change and food security. Science 304: 1623-1627.

MEA. 2005. Millennium Ecosystem Assessment -- Ecosystems and Human Well-being: Desertification Synthesis. World Resources Institute, Washington, DC, USA.