Document Type

Dissertation - Open Access

Award Date

1972

Degree Name

Doctor of Philosophy (PhD)

Department

Plant Science

First Advisor

E.M. White

Abstract

Nitrate movement in freezing and frozen soils was studied in both disturbed and undisturbed soils by laboratory and field investigations. Thermoelectric cooling plates were placed in insulated freezing boxes. Soil cores placed in the freezing boxes were stored, frozen, or thawed at a specific temperature or temperature gradient. Field plots and soils columns reset into the field environment were used to observe migration of either fall- or winter-applied nitrate. Movement of surface applied nitrate was caused by passage of a freezing front through either saturated or unsaturated sand or saturated Vienna loam. The nitrate movement due to freezing was greater in unsaturated sand than in saturated sand possibly due to the formation of more brine pockets in the saturated sand. Movement of nitrate from the surface of different kind of clay-sand mixtures maintained at -5 C was influenced by clay type, kind of exchangeable cation, and soil moisture content. Negative adsorption of nitrate by clay surfaces and the formation of thin ice lenses which interrupted liquid-film continuity probably were the major factors affecting nitrate movement. Nitrate applied to a frozen, saturated Kyle clay or Vienna loam moved more when it was applied to the -0.5 C rather than the -3.3 C Soil-column end. This difference was not found for Egeland sandy loam. In an experiment with freezing and thawing Vienna-loam columns nitrate moved with water toward the concentrated (warm) end of the core during the thaw cycle. Fall-applied nitrate moved more than winter-applied nitrate in soil cores for two separate years in the field studies. Nitrate appeared to have moved down to 30-cm depth in the field plots after either a fall or winter nitrate application. Mechanisms for nitrate movement in addition to salt rejection from the ice in the freezing soil solution, movement with mass flow of water, and diffusion due to concentration gradients could be caused by the Soret effect and brine-pocket migration.

Library of Congress Subject Headings

Soils -- Nitrogen content
Nitrates
Soil freezing

Format

application/pdf

Number of Pages

86

Publisher

South Dakota State University

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