Soil's carbon storage capacity in...( Madison WI July 28 2008--As atmosphe...)

Madison, WI July 28, 2008--As atmospheric CO2 levels rise, methods to mitigate these increases are becoming very important. Three studies published in the July-August 2008 issue of Soil Science Society of America Journal explore the potential roles of soils as a C sink in different regions in the Western Hemisphere. Scientists from Alberta Agriculture and Rural Development (Canada), the National Institute of Agricultural Technology, the University of Buenos Aires (Argentina), and University of California, Davis (USA) have investigated soil C balance in distinct agroecosystems under different management practices including soil tillage, N fertilization, elimination of fallow, and establishment of grass. In each case, C sequestration occurred in response to higher C input to soil; however, increase in SOC was confined to labile fractions such as the light fraction and larger soil aggregates.

Investigation: Canada

In southeastern Alberta, a long-term study showed previously that eliminating summer fallow or establishing grass significantly increased soil organic C after 6 yr. In the 12th year of the study, total organic C and light fraction C were determined in three rotations with summer fallow, two continuously cropped rotations and grass. All rotations had subtreatments with different levels of fertilization. The light fraction of soil C was obtained using density separation and consisted mostly of non-decomposed root and straw fragments.

Although soil organic C was increased by elimination of summer fallow, fertilization, and establishment of grass, gains in soil organic C between Years 6 and 12 were negligible in all treatments except the fertilized grass treatment. Most of the gains in total soil organic C were due to increased light fraction C. The results indicate that much of the gain in soil organic C in response to improved practices on semiarid prairie soils likely occurs within one decade.

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