Saturday, 15 July 2006

Redox Development in Soil Materials as Influenced by Time, Temperature, and Carbon Level.

Rebecca A. Blue1, Douglas D. Malo1, Thomas E. Schumacher1, James J. Doolittle2, and Jennifer J. Lund1. (1) South Dakota State Univ, SNP 247, Box# 2140C, Brookings, SD 57007, (2) South Dakota Agricultural Experiment Station, South Dakota State Univ, Ag Hall 129, Box 2207, Brookings, SD 57007-0291

The management of land and land use restrictions are defined and impacted by our understanding of hydric soils, therefore it is important that we understand the factors that affect the formation of hydric soils and redoximorphic conditions. Currently, the criterion for a hydric soil is defined as a soil that must be frequently flooded or ponded for seven days or longer with soil temperatures of greater than or equal to 5C. All soils are subjected to the same criterion, however, a number of other factors impact the formation of these conditions. The objective of this study is to observe and quantify the development of redoximorphic features in saturated soils as a function of (i) time, (ii) temperature, and (iii) carbon level. The soil collected for the experiment is representative of till parent material from eastern South Dakota. The treatment combinations were seven time periods (ranging from 7 to 336 days), four temperatures (5, 10, 20, and 40C) and three carbon levels (low, moderate, and high). The samples were analyzed at each time interval to observe the treatment effects on the reduction of elements (Fe and Mn), color development, soil pH and redox potential (Eh), and the time needed for the formation of redoximorphic features. Both temperature and carbon level significantly impacted soil Eh and color development over time. As temperature and carbon level increased, soil Eh decreased, and grayer soil colors were reached at a significantly more rapid rate. At 5C (the critical temperature), high carbon levels significantly reduced soil Eh by day 4 and for moderate carbon levels reduced Eh values were reached by day 7. However, the Eh of the low carbon treatment did not have the same trend and did not exhibit reducing conditions. Redox feature development first appeared at 28 days in the 40C and low carbon level treatment, while none were noted in any of the 5C treatments after 126 days. Results of this study demonstrate that the current hydric soil definition needs to be refined for the environmental conditions in the northern U.S. This study better defines the hydric soil criterion and assists farmers and natural resource managers in their management and policy decisions.

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