Major Procedural Discrepancies in Soil Extracted Nitrate Levels and Nitrogen Isotopic Values

Authors

  • Charles W. Lindau,

    1. Assistant Professor and Professor, respectively, Conservation and Survey Division, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, Nebraska 68588–0517.
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  • Roy F. Spalding

    1. Assistant Professor and Professor, respectively, Conservation and Survey Division, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, Nebraska 68588–0517.
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  • Discussion open until November 1, 1984.

  • Charles W. Lindau received his B.S. (1969) in Chemistry from Kearney State College, his M.S. in Chemical Oceanography from Texas A & M University (1974), and his Ph.D. from Texas A & M University (1980) in Soil Chemistry. He is presently an Assistant Professor with the Conservation and Survey Division where his interests include source identification of nitrates in ground water and stable isotope technology.

  • Roy F. Spalding received his B.A. (1966) in Chemistry from Kenyan College and his M.S. (1968) in Environmental Sciences and Engineering from the University of North Carolina. He received his Ph.D. in Oceanography (1972) from Texas A & M where he was involved with research concerning the contemporary geochemistry of uranium. Presently he is a Professor and Principal Hydrochemist with the Conservation and Survey Division where his interests include uranium geochemistry, source identification of nitrates in ground water, and mineral phase equilibria reactions.

ABSTRACT

Preliminary vadose zone nitrate extraction experiments have revealed the extractant (2N KCl) volume affects the determination of nitrate and its nitrogen isotope ratio.

In five cores, extractable NO3-N concentrations increased an average of 1.7 times after the soil-to-extractant ratio was increased from 1:1 to 1:10. An increased extractant volume resulted in a large positive shift of stable nitrogen values (δ15N), which averaged +6.2%.

An underestimation of available NO3-N for leaching and transport through the vadose zone and a biased source interpretation from the δ15N values probably would occur if a procedure which leads to incomplete extraction of nitrate is used.

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