Crop uptake, nitrification, and denitrification in a continuous corn agroecosystem

McSwiney, C. and G.P. Robertson

Presented at the ASM in Seattle (2003-09-18 to 2017-12-05 )

One of the most important proximal controls on N2O production in soils is N availability. In 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 day-1) up to 101 kg N ha-1 additions where grain yields were maximized, after which fluxes increased sharply. Two mechanisms that might explain the nonlinear response in N2O production to incremental N addition are differential uptake of N by the crop and changes in microbial processes responsible for N2O production across the N gradient. In 2003, N, as granular urea, was applied at nine levels from 0-292 kg N ha-1 yr-1 to 4 replicate fields in continuous corn and then incorporated. Plots were irrigated to alleviate water stress in the corn crop. We measured surface N2O fluxes after fertilization in plots where the corn was removed and in plots where the crop was left intact. Nitrification and denitrification assays were conducted to determine the relative importance of each of these processes in N2O production across the N gradient. Corn yields were determined at harvest and soil mineral N was determined at each flux measurement. The N2O flux response to the fertilizer gradient was linear in plots without corn and was nonlinear in plots with the crop.

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