Document Type

Thesis - University Access Only

Award Date

2006

Degree Name

Master of Science (MS)

Department / School

Agronomy

Abstract

The identification of hydric soils is one of three necessary criteria to identify a wetland, and by federal law such a designation has large impacts on the development potential and management of land. A hydric soil is defined as a soil that forms under conditions of saturation, flooding or ponding long enough in the growing season to develop anaerobic conditions in the upper part. To determine whether a soil meets the criterion of anaerobic conditions, the Natural Resource Conservation Service (NRCS) and the National Technical Committee for Hydric Soils (NTCHS) have developed several methods. The first of these methods is experience based, where certain soil morphological indicators are used in the field to identify hydric soils. The second is a field test using alpha,alpha-dipyridyl dye which indicates the presence of reduced iron (and anaerobic conditions). A third way to determine the possible anaerobic state of the soil is to measure and plot the redox potential (Eh) and pH of the soil according to the technical standard. The objective of this study was to gain a better understanding of hydric soils in the northern Midwest by observing and quantifying the trends in reduction and the formation of redox features in saturated soil material as a function of time, temperature, and carbon ( C) level. The soil used in the experiment was collected from the Bw horizon of a Vienna series (Calcic Hapludoll), and is representative of a typical till parent material from eastern South Dakota. The treatment combinations applied to the soil samples consisted of seven time periods (ranging from one week to 48 weeks), four temperatures (5°, 10°, 20°, and 40°C), three C levels (low, moderate, and high), and four replications (complete block design). The samples were analyzed at each time interval to observe the treatment effects on color development, the formation of redoximorphic features, the reduction of chemical species, soil pH, and redox potential (Eh). In addition, a side experiment was conducted to observe the effect of different native organic C levels taken from five soil horizons in the same Vienna soil. The results of this study indicate that C level, more than temperature, affects the redox chemistry of the soil. Carbon level determines the Eh/pH path in the soil systems, while temperature dictated the treatments' progression along the path. The importance of C was also apparent in the occurrence of Fe2+, and the ratio of oxalate- to dithioniteextractable iron. Carbon and temperature levels affected the rate of redox concentrations, with the highest C and temperature levels producing Fe concentrations in the least amount of time. However, soil matrix color changes were minimally affected by C and temperature treatments, with all experimental units, including the low C treatment, tending toward yellower hues over the course of the experiment, despite vastly different soil redox states.

Library of Congress Subject Headings

Hydric soils -- Middle West

Soil moisture

Oxidation-reduction reaction

Format

application/pdf

Number of Pages

85

Publisher

South Dakota State University

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