Nitrous oxide emissions from fertilized, irrigated cotton (Gossypium hirsutum L.) in the Aral Sea Basin, Uzbekistan : Influence of nitrogen applications and irrigation practices

Abstract Nitrous oxide emissions were monitored at three sites over a 2-year period in irrigated cotton fields in Khorezm, Uzbekistan, a region located in the arid deserts of the Aral Sea Basin. The fields were managed using different fertilizer management strategies and irrigation water regimes. N 2 O emissions varied widely between years, within 1 year throughout the vegetation season, and between the sites. The amount of irrigation water applied, the amount and type of N fertilizer used, and topsoil temperature had the greatest effect on these emissions. Very high N 2 O emissions of up to 3000 μg N 2 O-N m −2  h −1 were measured in periods following N-fertilizer application in combination with irrigation events. These “emission pulses” accounted for 80–95% of the total N 2 O emissions between April and September and varied from 0.9 to 6.5 kg N 2 O-N ha −1. . Emission factors (EF), uncorrected for background emission, ranged from 0.4% to 2.6% of total N applied, corresponding to an average EF of 1.48% of applied N fertilizer lost as N 2 O-N. This is in line with the default global average value of 1.25% of applied N used in calculations of N 2 O emissions by the Intergovernmental Panel on Climate Change. During the emission pulses, which were triggered by high soil moisture and high availability of mineral N, a clear diurnal pattern of N 2 O emissions was observed, driven by daily changes in topsoil temperature. For these periods, air sampling from 8:00 to 10:00 and from 18:00 to 20:00 was found to best represent the mean daily N 2 O flux rates. The wet topsoil conditions caused by irrigation favored the production of N 2 O from NO 3 − fertilizers, but not from NH 4 + fertilizers, thus indicating that denitrification was the main process causing N 2 O emissions. It is therefore argued that there is scope for reducing N 2 O emission from irrigated cotton production; i.e. through the exclusive use of NH 4 + fertilizers. Advanced application and irrigation techniques such as subsurface fertilizer application, drip irrigation and fertigation may also minimize N 2 O emission from this regionally dominant agro-ecosystem.