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Reduction of Nitrate in a Soil Column during Continuous Flow¹

ABSTRACT

A column packed with a homogenous Hanford sandy loam soil was perfused continuously with a solution containing 200 ppm NO₃^--N and 2400 ppm glucose-C. Weekly estimates of denitrifiers showed that populations increased from 10² to > 10⁸/g of soil. Denitrifiers were most abundant near the surface where NO₃^--N almost totally disappeared from the soil solution. An organic matter profile characterized by a surface layer developed within 3 weeks. Accumulated organic N accounted for about 4% of the total applied NO₃^--N while the remaining 96% disappeared, presumably by dissimilation, within the top 0.5 cm of the surface layer. Normalized rate constants from 1.2 x 10^-5 to 2.3 x 10^-5 ppm/hour cm³ per organism were estimated for dissimilation of NO₃^--N from its profiles.

In a similar experiment, but without added glucose, less of the NO₃^--N disappeared from solution; the percentage decreased from 40 to 15% with time. Denitrifiers were less numerous in the absence of glucose and were more uniformly distributed throughout the column. No appreciable changes in total soil carbon and nitrogen were detected during 7 weeks of perfusion with a solution of 200 ppm of NO₃^--N under these conditions.

¹ Contribution from the College of Natural Resources, University of California, Berkeley 94720. Supported by the Kearney Foundation of Soil Science and RANN of the National Science Foundation Grant no. G134733X.

² Assistant Research Chemist, Graduate Research Assistant, and Professor of Soil Biology, respectively, Univ. of Calif., Berkeley.

Received for publication June 10, 1974. Accepted for publication November 6, 1974.