Soil oxygen concentrations across a topographicgradient

McSwiney, C.P. and G.P. Robertson

Presented at the All Scientist Meeting (2004-10-08 )

One of the most important and least studied proximal controls on nitrous oxide production is soil oxygen concentration which affects the end-products of the processes of nitrification and denitrification, both of which produce this important radiatively active trace gas.  In past studies conducted at the W.K. Kellogg Biological Station in southwest Michigan in 2001 and 2002, we determined that N2O fluxes measured across a high resolution N gradient were moderately low (<50 g N2O-N ha-1 d-1) up to 101 kg N ha-1 additions where grain yields were maximized, after which fluxes increased sharply, yet variably across the four replicates studied. Differences in soil water content and soil O2 across this soil textural and topographic gradient may help explain the variability in N2O response to N addition.  In 2003, N was applied as granular urea at nine levels from 0-291 kg N ha-1 to four replicate fields in continuous corn.  Plots were irrigated to alleviate water stress in the crop.  We measured surface N2O fluxes, N availability, and soil water content before and at two week intervals after fertilization.  In 2004, we measured soil O2 after irrigation events on the same plots.  Nitrous oxide fluxes were greatest where soil O2 was most variable and soil water contest was least variable.

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