Wednesday, November 15, 2006

Redox Development in Soil Materials as Influenced by Time, Temperature, and Carbon Level - Part B: Chemical Changes.

Rebecca Blue1, Douglas Malo2, Thomas Schumacher3, James Doolittle4, and Jennifer Lund1. (1) South Dakota State Univ, Npb 247, Brookings, SD 57007, (2) Box 2140C SNP 247C, Plant Science Dept, SDSU, Brookings, SD 57007-2141, (3) NPB 247A, Box 2140C, South Dakota State Univ, Brookings, SD 57007, (4) Plant Science Dept, SDSU, 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, hydric soils are defined as soil that forms under conditions of saturation, flooding or ponding long enough during the growing season to develop anaerobic conditions in the upper part.  All soils are subjected to the same criteria, however, additional factors impact the formation of these conditions.  The objective of this study was to observe and quantify the chemical changes that occur in saturated till soil as a function of time, temperature, and carbon level.  The soil used in the experiment was collected from the Bw horizon of a Vienna series (Calcic Hapludoll), representing a typical till parent material from eastern South Dakota.  The treatment combinations applied included eight time periods (ranging from 1-48 weeks), four temperatures (5º, 10º, 20º, and 40ºC) and three carbon levels (low, moderate, and high).  Samples were analyzed at each time interval to observe treatment effects.  Carbon level, more than temperature, affected the soil redox chemistry.  Carbon level determined the Eh/pH path in the soil systems, while temperature dictated the treatments’ progression along the path.  Anaerobic conditions obtained in the higher carbon treatments were more powerfully reducing relative to the aerobic conditions that occurred in the low carbon treatments, resulting in more uniform reduction of iron and manganese in the higher carbon treatments.  pH varied by carbon level, with significantly lower values in the higher carbon (glucose amended) treatments.  Results of this study demonstrate that time, temperature, and carbon level influence the behavior of Eh, pH, and reducing conditions, verifying the need for a more precise definition of hydric soils that incorporates additional soil factors (such as carbon level and temperature) that impact hydric soil formation.

Handout (.pdf format, 105.0 kb)