Factors driving nitrous oxide emissions from uncropped (head ditch and tail drain) areas of irrigated cotton fields after water-run urea application

Abstract

Key findings •• A soil and sediment survey of 10 irrigated cotton paddocks across four cotton-growing valleys revealed the tail drain sediments were enriched in organic carbon (1.03% ± 0.05) and nitrogen (0.11% ± 0.01) compared with head ditch soils (0.73% ± 0.07 for carbon and 0.08% ± 0.01 for nitrogen) of the same paddocks. Nitrate-nitrogen and dissolved organic carbon analyses showed similar trends. •• After irrigation, tail drain samples tended to release more nitrous oxide compared with head ditch samples. Emission rates were linked to the pre-irrigation mineral nitrogen concentrations of the soil/sediments. •• These non-cropped areas, representing up to 2% of the paddock area, are a significant source of nitrous oxide emission per unit area of farm as they retain high soil moisture and nutrient concentrations in the absence of plants. •• Nitrous oxide emission calculations for cotton farming systems should incorporate the emissions from head ditch and tail drain sections of the irrigation network.