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Title: DISTRIBUTION OF LIGHT AND HEAVY FRACTIONS OF SOIL ORGANIC CARBON AS RELATED TO LAND USE AND TILLAGE PRACTICE

Author
item TAN, Z - THE OHIO STATE UNIV.
item LAL, R - THE OHIO STATE UNIV.
item Owens, Lloyd
item IZAURRALDE, R - UNIVERSITY OF MARYLAND

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2006
Publication Date: 1/8/2007
Citation: Tan, Z.X., Lal, R., Owens, L.B., Izaurralde, R.C. 2007. Distribution of light and heavy fractions of soil organic carbon as related to land use and tillage practice. Soil & Tillage Research. 92:53-59.

Interpretive Summary: Changes in total soil organic carbon (SOC) occur with changes in land use and management. Several factors influence how carbon is stored in soil including soil fractions based on density. Carbon storage in light and heavy soil fractions was evaluated under conventional tillage, no-till, and forest treatments. The light fraction is more plant-like and has a less stable C concentration. Soils under no-till and forest preserved more of the light fraction than soils under conventional tillage. There was more SOC in all aggregate classes under no-till and forest than under conventional tillage. This suggests that there is greater protection of SOC by aggregates in soil that is less disturbed. The SOC loss caused by conversion of forest to agricultural land use is attributed to C reduction in both light and heavy soil fractions, while the SOC gain following conversion from conventional tillage to no-till occurs predominantly in the light fraction. This information is useful to other scientists and land use planners, especially those planning land use to improve soil quality.

Technical Abstract: Mass distributions of different soil organic carbon (SOC) fractions are influenced by land use and management. Concentrations of C and N in light- and heavy fractions of bulk soils and aggregates in 0 – 20 cm were determined to evaluate the role of aggregation in SOC sequestration under conventional tillage (CT), no-till (NT), and forest treatments. Light- and heavy fractions of SOC were separated using 1.85 g mL-1 sodium polytungstate solution. Results showed that soils under forest and NT preserved, respectively, 167% and 94% more light fraction than those under CT. The mass of light fraction decreased with increase in soil depth, but significantly increased with increase in aggregate size. C concentrations in light fraction in all aggregate classes were significantly higher under NT and forest than under CT. C concentrations in heavy fraction averaged 20, 10, and 8 g kg-1 under forest, NT, and CT, respectively. Of the total SOC pool, heavy fraction C accounted for 76% in CT soils and 63% in forest and NT soils. These data suggest that there is a greater protection of SOC by aggregates in the light fraction of minimally-disturbed soils than that of disturbed soil, and the SOC loss following conversion from forest to agriculture is attributed to reduction in C concentrations in both heavy and light fractions. In contrast, the SOC gain upon conversion from CT to NT is primarily contributed by increase in C concentration in the light fraction.