Assessment of Nitrous Oxide and Methane Emissions In Rice Based Cropping Systems.

Approaches to measuring N₂O and CH₄ emissions from rice based cropping systems are briefly discussed.  Accurate assessment of annual fluxes requires continuous monitoring.  For paddy rice, CH₄ emissions occur with continuous flooding, i.e. under highly reduced conditions, and are increased substantially by organic material additions.  In contrast N₂O, emissions occur under times of transition to and from flooding and during wet periods for any rotational upland crops.  Intermittent drainage of rice paddies to reduce CH₄ emissions leads to conditions where N₂O can be emitted thus creating a trade-off between the two greenhouse gases.  Volatilization of NH₃ before canopy closure is also a common nitrogen loss mechanism in rice paddies.  Atmospheric NH₃ reactions with acidic species promote smog formation, and its deposition on plant and land surfaces can contribute to off-site emissions of N₂O.