Nitrous Oxide Emissions from Irrigated Cotton and Guayule in Arizona.

Nitrogen fertilizer is a source of the potent greenhouse gas nitrous oxide (N₂O) in irrigated cropping systems.  However, very little data exists for row crops in the desert southwest of North America, where seasonal irrigation amounts can exceed 1 m.  The objective of these studies was to assess the magnitude of varying N fertilizer rates on N₂O emissions from surface-irrigated cotton (Gossypium hirsutum) and guayule (Parthenium argentatum) in field studies in Central Arizona.  Guayule was transplanted in October on 1-m wide beds, and cotton was planted in late April to 1 May on 1-m wide beds.  Emissions were measured using 1-L vented chambers placed for 24 minute periods in the bottom of the furrows.  Samples were taken at 0, 12, and 24 minutes.  In cotton N₂O emissions were measured from May to August, and in guayule fluxes were determined for the 24 months guayule was grown.  Nitrogen rates varied from 0 to 112 kg N ha^-1 in cotton (two splits) to 0 to 336 kg N ha^-1 in guayule (four splits across 12 months).  Nitrous oxide emissions were not agronomically significant and were greatest in the guayule field on a sandy loam vs.  cotton on a sandy clay loam.  Emissions were positively correlated with soil moisture and temperature.  Nitrous oxide fluxes ended 2-3 d after irrigation events that consisted of 8 to 15 cm water.