Wednesday, November 15, 2006 - 9:45 AM

Soil Horizons and Native Organic Carbon: Physical and Chemical Changes in Saturated Soil Material.

Rebecca Blue1, Douglas Malo2, Thomas Schumacher3, James Doolittle4, and Jennifer Lund1. (1) South Dakota State Univ, NPB 247, Brookings, SD 57007, (2) SDSU, Plant Science Dept, Box 2140C SNP 247C, Brookings, SD 57007-2141, (3) NPB 247A, Box 2140C, South Dakota State Univ, Brookings, SD 57007, (4) SDSU, Plant Science Dept, NB247D Box 214OC, Brookings, SD 57007-2141

Land management and restrictions are impacted by our understanding of hydric soils, emphasizing the importance of understanding the factors that affect the formation of hydric soils and redoximorphic conditions.  Currently, a hydric soil is defined as a soil that forms under conditions of saturation, flooding or ponding long enough during the growing season to develop anaerobic conditions in the upper part.  Organic carbon is considered among the most important factors in the development of these anaerobic conditions.  The objective of this study was to test the susceptibility of five soil horizons from a single profile to changes in redox chemistry and the formation of redox features over time in a saturated till soil.  Treatment combinations applied included four time periods (1, 3, 12, and 24 weeks), one temperature (20ºC), and five soil horizons (Ap, AB, Bw, 2Bk, and 2C) which represented five different organic carbon levels (3.68%, 1.43%, 0.73%, 0.30%, and 0.21%) from a Vienna series (Calcic Hapludoll).  Eh/pH behavior of the soil systems differed with each horizon.  The Ap horizon, containing the highest carbon level, reached anaerobic conditions by day 1.  However, the Bk and C horizons, containing the lowest organic carbon and highest pH values, remained aerobic throughout the study.  Overall,  >70% of the variation in Eh among the soil systems in the study was attributed to organic carbon level.  Iron and manganese reduction correlated with the soil’s aerobic/anaerobic state, and redox feature development was observed in the Ap, AB, and Bw horizons at 12 and 24 weeks.