Degree Type

Dissertation

Date of Award

1987

Degree Name

Doctor of Philosophy

Department

Agricultural and Biosystems Engineering

Abstract

Pressure extraction of solution from a soil- NO[subscript]3-N solution slurry using a pressure-plate apparatus revealed that NO[subscript]3-N concentrations in the extracts decreased as pressure was progressively increased. This was interpreted as being the effect of anion exclusion. The relationships between the extract concentration and the applied air pressure (or moisture content) are discussed;Results from the study of laboratory and field columns subjected to freezing conditions showed that there was a significant accumulation of moisture and NO[subscript]3-N in the frozen layer (upper zone) and depletion from the lower unfrozen zone. Maximum accumulation was usually observed above but near the frozen-unfrozen interface; maximum depletion was usually from the layer immediately below this interface. The amount of accumulation increased with increasing soil moisture and duration of freezing. Highest accumulation was observed in columns with the bottom immersed in solution at a constant elevation, as opposed to closed columns. Exclusion of anions from the soil solution appeared to be a factor that enhanced upward NO[subscript]3-N movement as long as moisture was moving in the liquid phase from the unfrozen zone. Within the frozen zone, accumulation of NO[subscript]3-N in the top layer may have been due partly to movement of a relatively concentrated solution through the frozen soil pores. Water vapor movement was small, but its dominance relative to the liquid phase movement increased with decreasing moisture content from 20 to 9.4%. Therefore, upward anion movement was much decreased in soils with moisture contents less that 20%;For field columns open at both ends, the increase in the amount of NO[subscript]3-N near the frozen-unfrozen interface was believed due to both upward moisture and NO[subscript]3-N movement, as well as movement with water moving from above through the frozen soil pores during freeze-thaw cycles. In-situ soil sampling on December 6, 1985 showed a 37% (20 kg/ha) increase in NO[subscript]3-N of the soil profile after one month of freezing;Spring thaw redistributed moisture and NO[subscript]3-N contents in the closed closed columns essentially back to their initial distributions with depth. Snow and soil solution thawing, and rainfall infiltration in the spring resulted in downward redistribution and leaching of NO[subscript]3-N from the columns and field soil profile.

DOI

https://doi.org/10.31274/rtd-180813-11640

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Gregorio Jamilo Galinato, Jr.

Language

en

Proquest ID

AAI8721883

File Format

application/pdf

File Size

255 pages

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