Effect of pH on the Rate of Gaseous Products of Denitrification in a Silt Loam Soil

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Abstract
To examine the effect of soil pH on the rate and products of denitrification, a silt loam soil (Typic Argiudoll) was used that had been collected from a field experiment maintained at various pH levels for 18 years. The soil pH ranged from 4.6 to 6.9 and was nearly uniform in organic C (1.15 ± 0.05%) and texture. Incubation was performed under He in all‐glass systems that were sealed throughout the incubation period. The soils were amended with 100 µg/g of NO‐3‐N before incubation. Denitrification products (N2O, NO, and N2) and CO2 were determined by gas chromatography using an ultrasonic detector.It appears that the rate of organic C mineralization rather than pH controls the rate of denitrification in C‐limited systems. At 100 µg NO‐3‐N added per gram of soil, the overall rates of denitrification correlated with the rates of C mineralization (CO2 evolution) but were not consistently related to pH or to total organic C.Soil pH did affect the products of denitrification. Nitrous oxide comprised 83% of the gaseous‐N products for pH 4.6 and 5.4 when 90% of the NO‐3 had been denitrified. The N2O was then rapidly reduced to N2. The highest amount of NO was observed at pH 4.6 and 5.4. At pH 6.0 the rate of production of N2O exceeded the rate of reduction only for the first 2 d of incubation. However, N2O was the dominant product until ∼83% of the NO‐3 had been denitrified. At pH 6.9, N2 was the dominant product after the 1st d of incubation.
Funding Information
  • College of Agricultural and Life Sciences
  • National Science Foundation (DEB 7817404)

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