Denitrification rates were studied under near‐anaerobic conditions in 30 soils of diverse origin that differed widely in pH, organic C contents, and other characteristics. Soils with added NO 3 ‐N were submerged in water and containers were sealed to prevent further oxygen intake during incubation. Disappearance of NO 3 ‐N and production of NH 4 ‐N were determined at 1‐day intervals or longer over a 10‐day period. Since soils were not shaken during incubation, denitrification rates were influenced by diffusion of nitrate from the liquid to the soil layer. In most soils, amounts of NO 3 ‐N declined exponentially with time of incubation. Thus, under the experimental conditions, the loss of nitrate was depicted better by log NO 3 ‐N vs. time ( t , hours) than ppm NO 3 ‐N vs. t . The apparent first‐order rate constants ( k ), denoting the fractional loss of NO 3 ‐N/hour, ranged from about 0.001 to 0.04 hour ‐1 . Correlations of k with total soil organic C and with soil “glucose‐C,” extracted by boiling soils for 1 hour in 0.01 M CaCl 2 , were highly significant. However, the extractable glucose‐C (an index of readily decomposable C sources) provided a more reliable basis for predicting k than did total organic C. The regression of k on glucose C ( X ) for 30 soils is as follows: k = 0.188 X − 0.00093, (r 2 × 100 = 82%). For the corresponding regression involving total organic C, r 2 × 100 = 69%. Within 24 to 48 hours, appreciable amounts of Mn appeared in solution and usually continued to increase with time. Reduced Fe did not appear until most of the NO 3 ‐N had disappeared. After 48 hours of incubation, the multiple regression of Mn ( Y ), in solution, on NH 4 ‐N produced ( X 1 ) and initial soil pH ( X 2 ), with associated statistics, was as follows: Y = 13.8 + 3.5 X 1 − 13.5 X 2 ( R = 0.77), r Y1.2 = 0.48. Values are significant at the 1% level.
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Stanford et al. (1975) studied this question.