Losses of nitrous oxide dissolved in drainage water from agricultural land

Abstract

DISCUSSIONS on the fate of nitrogen in soil usually assume that the gases produced by denitrification—nitrous oxide and molecular nitrogen—are lost only by movement in the gaseous phase towards the soil surface, where they escape to the atmosphere. As far as we know, there are no published reports of the transport of these gases dissolved in water draining from agricultural land. However, the anaerobic conditions necessary for denitrification develop to an appreciable extent in drained agricultural soils when the soil water potential is zero or positive^1–6; there is then likely to be drainage of water through the soil. In the soils of southern England, nitrous oxide can be found for extended periods during the wetter months^7–8, where there is on average ∼250 mm rainfall in excess of evapo-transpiration and soil storage⁹. As nitrous oxide is fairly soluble in water (1.0 ml gas per ml water at 5°C) we have examined the possibility that significant quantities are transported from the soil in drainage water. We report here for the first time observations that nitrous oxide can be lost from the soil by leaching in amounts comparable with those lost in the gas phase from the soil surface.