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Denitrification and Availability of Carbon and Nitrogen in a Well‐drained Pasture Soil Amended with Particulate Organic Carbon
Author(s) -
Stevenson Bryan A.,
Schipper Louis A.,
McGill Alexandra,
Clark Dave
Publication year - 2011
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2010.0463
Subject(s) - denitrification , denitrifying bacteria , mulch , environmental science , agronomy , sawdust , soil water , nitrate , woodchips , zoology , nitrogen , chemistry , environmental chemistry , soil science , ecology , biology , organic chemistry
A well‐drained soil in N‐fertilized dairy pasture was amended with particulate organic carbon (POC), either sawdust or coarse woody mulch, and sampled every 4 wk for a year to test the hypothesis that the addition of POC would increase denitrification activity by increasing the number of microsites where denitrification occurred. Overall mean denitrifying enzyme activity (DEA), on a gravimetric basis, was 100% greater for the woody mulch treatment and 50% greater for the sawdust treatment compared with controls, indicating the denitrifying potential of the soil was enhanced. Despite differences in DEA, no difference in denitrification rate, as measured by the acetylene block technique, was detected among treatments, with an average annual N loss of ∼22 kg N ha −1 yr −1 Soil water content overall was driving denitrification in this well‐drained soil as regression of the natural log of volumetric soil water content (VWC) against denitrification rate was highly significant ( r 2 = 0.74, P < 0.001). Addition of the amendments, however, had significant effects on the availability of both C and N. An additional 20 to 40 kg N ha −1 was stored in POC‐amended treatments as a result of increases in the microbial biomass. Basal respiration, as a measure of available C, was 400% greater than controls in the sawdust treatment and 250% greater than controls in the mulch. Net N mineralization, however, was significantly lower in the sawdust treatment, resulting in significantly lower nitrate N levels than in the control. We attribute the lack of measured response in denitrification rate to the high temporal variability in denitrification and suggest that diffusion of nitrate may ultimately have limited denitrification in the amended treatments. Our data indicate that manipulation of denitrification by addition of POC may be possible, particularly when nitrate levels are high, but quantifying differences in the rate of denitrification is difficult because of the temporal nature of the process (particularly the complex interaction of N availability and soil water content).