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

Abstract

It is often assumed that the N2O produced from nitrification and denitrification in soil systems is lost primarily as a gas from the soil surface. However, the dissolution and eventual degassing of N2O in water leaching through, and draining from, agricultural fields is also a significant loss pathway. The quantification of this pathway of N2O 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™ 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 redsucing the N2O 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 N2O 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 N2O degassing such that N2O concentration did not decrease significantly in the first 24 h after filling of the bottle.