HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Allred, B. J. Articles by Brown, G. O. Search for Related Content PubMed Articles by Allred, B. J. Articles by Brown, G. O. GeoRef GeoRef Citation Agricola Articles by Allred, B. J. Articles by Brown, G. O. Related Collections Soil Hydrology Soil Mineralogy Vadose Zone Processes and Chemical Transport

ORIGINAL RESEARCH

The Impact of Clay Mineralogy on Nitrate Mobility under Unsaturated Flow Conditions

^a USDA-ARS Soil Drainage Research Unit, 590 Woody Hayes Dr., Rm. 234, Columbus, OH 43210
^b School of Natural Resources, Ohio State Univ., 2021 Coffey Rd., 210 Kottman Hall, Columbus, OH 43210
^c Biosystems and Agricultural Engineering Dep., Oklahoma State Univ., 109 Agricultural Hall, Stillwater, OK 74078
^* Corresponding author (allred.13{at}osu.edu).

Received 27 April 2006.

Transient unsaturated horizontal column experiments were conducted to assess clay mineralogy impacts on electrostatic processes affecting nitrate (NO₃^–) mobility. Replicated tests were conducted on quartz sand, mixtures of the sand and kaolinite, illite, and montmorillonite, and two natural soils with organic matter removed. In each test, a 200 mg L^–1 nitrate–nitrogen (NO₃^––N) solution was injected at the inlet of dry soil columns. Comparison of corresponding NO₃^––N concentration and volumetric water content profiles from the column tests provided valuable information regarding soil mineral composition impacts on NO₃^– transport. With the exception of a small peak at the wetting front, NO₃^––N concentrations for the quartz sand were consistently near the 200 mg L^–1 injection level within the wetted portion of the columns, indicating that NO₃^– electrostatic interactions were negligible. Anion adsorption processes in the 25% kaolinite–75 % sand mixture produced a result in which the NO₃^––N concentrations adjacent to the inlet of the columns were approximately 20% greater than that of the injected solution. Anion exclusion was the dominant electrostatic interaction affecting NO₃^– mobility in the 25% illite–75% sand, 25% montmorillonite–75% sand, and 15% kaolinite–7.5% illite–7.5% montmorillonite–70% sand mixtures and in the two natural soils. Evidence of anion exclusion in these artificial and natural soils includes NO₃^––N concentrations near the column inlet that were 11 to 19% less than the injected solution concentration, and NO₃^––N concentrations near the wetting front that were greater than the injected solution concentration by factors of 1.7 to 5.4. These results indicate that anion adsorption is an important process affecting NO₃^– mobility in low pH soils, with limited amounts of organic matter, and having a clay-size fraction dominated by kaolinite, while anion exclusion is a key electrostatic interaction influencing NO₃^– mobility in near-neutral to high pH soils, especially if significant amounts of montmorillonite are present.

Abbreviations: CEC, cation exchange capacity • PZC, point of zero charge • XRD, X-ray diffraction.