Reduction of Nitrate in a Soil Column during Continuous Flow

A column packed with a homogenous Hanford sandy loam soil was perfused continuously with a solution containing 200 ppm NO 3 ‐ ‐N and 2400 ppm glucose‐C. Weekly estimates of denitrifiers showed that populations increased from 10 2 to > 10 8 /g of soil. Denitrifiers were most abundant near the surface where NO 3 ‐ ‐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 NO 3 ‐ ‐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 × 10 ‐5 to 2.3 × 10 ‐5 ppm/hour cm 3 per organism were estimated for dissimilation of NO 3 ‐ ‐N from its profiles. In a similar experiment, but without added glucose, less of the NO 3 ‐ ‐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 NO 3 ‐ ‐N under these conditions.