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Nitrate Reduction and Associated Microbial Populations in a Ponded Hanford Sandy Loam

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1975

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Abstract

Abstract A field plot of Hanford sandy loam was ponded for 2 weeks with a solution of KNO 3 and Ca(NO 3 ) 2 containing 100 ppm NO 3 ‐N in order to measure short term denitrification rates as well as growth and distribution of bacteria capable of reducing nitrate to nitrite and/or N 2 O and N 2 . Denitrifying bacteria (10 1 −2.9 × 10 4 /g soil) generally decreased in number with depth and time and were not as numerous as nitrate reducers (10 1 −6.9 × 10 5 /g soil). In the top 60 cm of soil, the concentration of NO 2 − ‐N in soil solution corresponded to minima in NO 3 − ‐N, suggesting that NO 3 − reduction gave rise to the NO 2 − . Denitrification rates calculated for the top 16 cm of water‐saturated soil were estimated to range from 0.013 to 0.046 µ g N/hour g −1 . The highest value was about 80% of that measured in a laboratory soil column studied previously. This difference in denitrification rates may be due to lower soil carbon content in the field.