Preliminary study of N 2O flux over irrigated bermudagrass in a desert environment

Abstract

The increase of atmospheric nitrous oxide (N 2O) is believed to be related to human activities, including increased agricultural use of nitrogen (N) fertilizers and irrigation. The purpose of this study was to evaluate N 2O flux ( F N ) into the atmosphere using chamber and gradient profile methods over an irrigated, N fertilized, bermudagrass ( Cynodon dactylon cv. ‘Midiron’) field in the Sonoran Desert of Arizona. For the gradient profile method it was hypothesized that locally stable atmospheric conditions would enhance N 2O concentration differences sufficiently (more than approximately 4 nl 1 −1) to be resolved by gas chromatographic analysis of air samples collected at two heights (0.05 and 3.3 m) over the field. Significant differences (205 and 30 nl 1 −1) in mean concentration occurred during two sampling intervals in late afternoon and early morning of a 24 h period on 18–19 July 1991. During those intervals the surface layer was stable and relatively large F N estimated by the chamber method (371 and 48 ng m −2 s −1) were comparable with F N estimated by the gradient profile method (283 and 101 ng m −2 s −1). Simulations based on similarity theory indicate that resolution of N 2O concentration differences less than 1 nl 1 −1 was required, but could not be achieved, when the surface layer was unstable and/or F N was small. Analysis also indicates that uncertainty of F N estimated by the chamber method was reduced slightly by estimation of temporal variation of vapor pressure in chamber air.