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Title: IMPACT OF CONSERVATION TILLAGE ON SOIL CARBON IN THE `OLD ROTATION'

Author
item SIRI PRIETO, G - AUBURN UNIV.PH.D.STUD
item Reeves, Donald
item SHAW, J - AUBURN UNIVERSITY
item MITCHELL, C - AUBURN UNIVERSITY

Submitted to: Southern Conservation Tillage for Sustainable Agriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/24/2002
Publication Date: 6/24/2002
Citation: Siri Prieto, G., Reeves, D.W., Shaw, J.N., Mitchell, C.C. 2002. Impact of conservation tillage on soil carbon in the `old rotation.' In: Van Santen, E., editor. Proceedings of the 25th Annual Southern Conservation Tillage Conference for Sustainable Agriculture - Making Conservation tillage Conventional: Building a Future on 25 Years of Research. Special Report no. 1, Alabama Agricultural Experiment Station and Auburn University, June 24-26, Auburn, Alabama. p. 288-294.

Interpretive Summary: Long-term experiments provide valuable and unique resources for researching sustainable agricultural production. Soil carbon is the key to sustainability; cover crops, crop rotations and tillage practices impact levels of soil carbon. The `Old Rotation' at Auburn University is the oldest continuous cotton experiment in the world. ARS researchers, cooperating with Auburn University scientists, converted the `Old Rotation' to conservation tillage in 1997. We determined the impact of conservation tillage adoption on soil carbon in the `Old Rotation', after 100 years of conventional tillage (1896-1996). After 42 months, conservation tillage increased soil carbon concentrations 39%, averaged across all rotation treatments. These changes are linked to increases in yield during this period. The study confirms that conservation tillage had a dramatic impact on soil carbon, especially in the soil surface, and these changes occurred sooner than other research suggests. This information can be used by extension, NRCS, and private-sector consultants to promote the use of conservation tillage to improve soil quality and productivity.

Technical Abstract: The `Old Rotation', the oldest continuous cotton (Gossypium hirsutum L.) experiment in the world, provides a valuable and unique resource for researching sustainable agricultural production. The objective of this paper is to quantify the impact of conservation tillage adoption after 42 months (May 1996, last conventional tillage) on SOC in the `Old Rotation', after 100 years of conventional tillage (1896-1996). Although the 13 plots have undergone modifications since 1925, six basic cropping systems have been maintained: 3-yr cotton-corn (Zea Mays L.)-small grain/soybean (Glycine max [L] Merr.) + legume + nitrogen; continuous cotton without legume; continuous cotton + legume; continuous cotton without legume + nitrogen; 2-yr cotton-corn + legume; and 2-yr cotton-corn + legume + nitrogen. Soil organic carbon was determined by dry combustion from samples taken in 1994 (0-8 in depth) and again in 1999, 42 months after the last tillage event, (0-2 and 2-6 in depths). Soil organic carbon stratification ratios (SOC 0-2 in/SOC 2-6 in depths) were determined from samples taken in 1999. After 42 months, conservation tillage increased SOC concentrations 39 % averaged across all plots. These changes are linked to increases in yield during this period. The SOC stratification ratio in the `Old Rotation' in 1999 suggests that changes in soil quality from adoption of conservation tillage are in the initial stages. However, the study confirms that conservation tillage had a dramatic impact on SOC, and these changes occurred sooner than other research suggests.