Nitrate Reduction to Ammonium in Anaerobic Soil1
- R. J. Buresh and
- W. H. Patrick2
Knowledge regarding the pathway and soil conditions necessary for NO3- Conversion to NH4+ and organic N, a process which conserves soil N, is limited. The influence of rice straw (2.5 mg C/g soil), methanol (1.0 mg C/g soil), and glucose (1.0 mg C/g soil) on the fate of 100 µg/g 15N-labelled NO3--N was studied in Crowley silt loam. The fraction of the added NO3--N in the NO3-, N2, NH4+, and organic N forms was determined after 4-day incubations under an Ar atmosphere at 30°C. In glucose-amended soil 9 and 19% of the applied NO3--N was recovered as NH4+-N and organic N, respectively. A 1-day preincubation with glucose (0.5 mg C/g soil) before the 4-day incubation with added NO3- and glucose increased labelled NH4+-N and organic N recovery to 36 and 34% of the added NO3--N, respectively. The corresponding values for rice straw- and methanol-treated soil and soil containing no added energy source were each less than 5%.
Nitrate-N reduction to NH4+-N increased to 20.5% after a 4-day incubation when soil with no C amendment was incubated under Ar for 20 days before NO3- addition. The redox potential was −260 mV upon NO3- addition
Transformation of significant amounts of NO3- to NH4+ and organic N required intensely reduced soil conditions. The reaction was apparently not suppressed by NH4+. Evidence indicated that NO3- was reduced to NH4+ by a nonassimilatory pathway in which NO3- functioned as a terminal electron acceptor.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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