A simple method for quantifying dissolved nitrous oxide in tile drainage water

It is often assumed that the N sub(2)O produced from nitrification and denitriflcation in soil systems is lost primarily as a gas from the soil surface. However, the dissolution and eventual degassing of N sub(2)O in water leaching through, and draining from, agricultural fields is also a significant loss pathway. The quantification of this pathway of N sub(2)O loss has been limited by available methodologies for measuring dissolved gases in drainage water. Here a simple method is presented, which allows for the collection of tile drainage water samples using standard automated water sampling equipment that maintains the dissolved gases. Tile drainage water was collected in 1 L ISCO super(TM) water sampling bottles outfitted with modified 10 mL volumetric pipettes. The pipettes provide a means of reducing the water:atmosphere interface for water held within the pipette thus reducing the N sub(2)O exchange with the atmosphere. The water samples are removed from the pipette using long slender needles attached to a 20-mL syringe, drawing 5 mL of water from within the bulb of the pipette. The dissolved N sub(2)O in the water samples was measured by headspace analysis using a gas chromatograph. A laboratory trial determined that retaining the water in the pipette bulbs resulted reduced N sub(2)O degassing such that N sub(2)O concentration did not decrease significantly in the first 24 h after filling of the bottle.Original Abstract: On presume souvent que le N sub(2)O resultant de la nitrification et de la denitrification dans le sol se perd essentiellement sous forme de gaz qui s'echappe a la surface du sol. Cependant, la dissolution du N sub(2)O dans l'eau puis le degazage de cette derniere quand elle s'infiltre dans le sol par lixiviation ou drainage des champs agricoles peut aussi entrainer des pertes importantes de ce gaz. Jusqu'a present, les methodes existantes qui recueillent automatiquement les echantillons d'eau servant a doser le volume des gaz dissous dans l'eau de drainage restreignaient la quantification de ces pertes. Les auteurs proposent une methode simple permettant de recueillir l'eau drainee par des tuiles avec du materiel standard d'echantillonnage automatique tout en reduisant les pertes de gaz dissous. L'eau drainee est recueillie dans des bouteilles ISCO super(MC) d'un litre pourvue a l'exterieur d'une pipette volumetrique de 10 mL modiflee. La pipette diminue l'interface entre l'eau qu'elle contient et l'atmosphere, ce qui reduit les ec