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Soil Carbon Sequestration in Sorghum Cropping Systems: Evidence From Stable Isotopes and Aggregate-Size Fractionation

Dou, Fugen1,2; Hons, Frank M.2; Wright, Alan L.3; Boutton, Thomas W.4; Yu, Xian5

doi: 10.1097/SS.0000000000000045
Technical Article

Management practices can influence both the quantity of soil organic carbon (SOC) and its distribution into different fractions or pools. We investigated SOC sequestration potentials of cropping systems in near-surface (0–5 cm) samples through soil size and density fractionation coupled with acid hydrolysis and natural abundance of stable isotopes (δ13C) in a 20-year field study in the southern Great Plains in 2002. Treatments included two tillage regimens, conventional and no tillage (NT), in combination with two cropping systems: continuous grain sorghum [Sorghum bicolor (L.) Moench.] (CS) and a sorghum-wheat (Triticum aestivum L.)-soybean [Glycine max (L.) Merr.] (SWSoy) rotation, and with or without N fertilization. Tillage and cropping sequence significantly affected SOC distribution and the natural abundance of δ13C in different fractions. Samples from CS exhibited δ13C values ranging from −15‰ to −20‰, suggesting most SOC was derived from this C4 crop species. The δ13C values for soils from SWSoy varied from −20‰ to −22‰, reflecting a mixed input from C3-derived and C4-derived residue input. For whole soil and all aggregate-size fractions, SOC concentrations were significantly higher for NT than conventional tillage. However, the effects of cropping system and N fertilization on SOC interacted with tillage. Greater SOC for enhanced cropping (SWSoy) or N fertilization was observed only under NT. The fraction of <53 μm represented a greater proportion of soil than other aggregate-size fractions. Our long-term study indicated that SOC and its various fractions, including more resistant, can be increased by NT with enhanced cropping and N fertilization.

1Texas A&M AgriLife Research & Extension Center at Beaumont, Beaumont, TX.

2Department of Soil and Crop Sciences, Texas A&M University, College Station, TX.

3Everglades Research and Education Center, University of Florida, Belle Glade, FL.

4Department of Ecosystem Science and Management, Texas A&M University, College Station, TX.

5Department of Mathematics and Statistics, University of Arkansas at Little Rock, Little Rock, AR.

Address for correspondence: Fugen Dou, PhD, Texas A&M AgriLife Research & Extension Center at Beaumont, 1509 Aggie Dr, Beaumont, TX 77713; E-mail:

This material is based on work supported by the Cooperative States Research, Education, and Extension Service, USDA, under agreement no. 2001-38700-11092, by the Consortium for Agricultural Soils Mitigation of Greenhouse Gases (CASMGS).

Financial Disclosures/Conflicts of Interest: None reported.

Received September 23, 2013.

Accepted for publication April 7, 2014.

© 2014Wolters Kluwer Health | Lippincott Williams & Wilkins