Fluxes of Nitric Oxide From a Sugarcane Field

Abstract

Improved values for NOx fluxes from tropical agriculture are needed for global climate models. Fluxes of NO were measured in a drip-irrigated, fertilized tropical sugarcane field in Hawaii. The chamber approach was used to measure surface NO fluxes, and a flux-gradient approach, to measure above-canopy NOx fluxes. Soil water, NH/, and N03 - content, weather data, leaf area, etc. were measured to interpret the NO fluxes. Daily surface NO fluxes tended to increase and decrease concurrently with soil water content. Peak fluxes were large (typically l20 ng NO-N m-2 s- 1) for the drip line, but much smaller between the rows (10 ng NO-N m- 2 s- 1). Inair chemical reactions of the N0-03-N0 triad caused 2 divergence of NOx fluxes from inert values; the actual fluxes were calculated with the reactive eddy diffusivity model formulated by Jila-Guerau de Arellano and Duynkerke (NO fluxes were 0.5% larger). 03 interference with the chemiluminescent analyzer introduced large errors into some fluxes. Decreasing ratios of above-canopy NOx to surface NO fluxes late in the study are associated with increasing canopy cover. The NOx flux was comprised more of NO early in the study and N02, later. The 198-d average NO flux was 9 ng N m- 2 s- 1 which is comparable with other studies in fertilized and irrigated systems.