Rowlings D of Institute for Sustainable Resources, Queensland University of Technology and Grace P of Institute for Sustainable Resources, Queensland University of Technology. N2O and N2 emissions from irrigated cotton. Dalby, Queensland, 2007-2008 [GCRC].
Rowlings.33.9
(http://www.n2o.net.au/knb/metacat/Rowlings.33.9/html).
Cotton is one of many agricultural industries in Australia heavily reliant on nitrogenous fertilizers and water storages to maintain high levels of production. Cotton-based farming systems are therefore labelled as potentially high-risk agricultural systems with respect to gases losses of nitrogen to the atmosphere. The on-farm study was undertaken at Dalby in the Darling Downs region of Queensland in north eastern Australia. The field was furrow irrigated and had been under continuous cotton (with winter bare fallow) for 10 years. An automated greenhouse gas measuring system (developed by Butterbach-Bahl et al.) was utilised that consisted of six chambers connected to sequential sampling unit, a gas chromatograph (equipped with both electron capture and flame ionization detectors for nitrous oxide and methane analysis respectively), and a Licor for carbon dioxide. The experiment also directly measured the specific losses of N2O and N2 from a single application of N fertiliser using 15N isotopically labelled urea. As there was little residual N in the profile after the previous crop, the grower applied 200 kg starter N in August 2006, and planted in late October, 2006. An application of 15N labelled urea (99% atom excess 15N) was made on 2 November in three (of the six) gas sampling chambers equivalent to 120 kg N/ha (treatment A), and 60 kg N/ha equivalent in the remaining three chambers (Treatment B). The grower applied 23 and 46 kg N as urea in the irrigation water, 98 and 135 days after the 15N urea was applied.
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17/09/2007 to 05/05/2008 Darling Downs (near Dalby), Southern Queensland, Australia (-27.3536, 151.4416)
Two sets of (3) chambers were placed (over plants) on 2 rows of irrigated cotton (3 per row) approximately 7 m apart and managed as per farmer practice. Over the season a total of 155 kg N was added as both anhydrous ammonia and water run urea. An additional application of 99% enriched 15N labled urea was applied on the 28.12.2007 at rates of 40 kg N (chambers 1-3) and 80 kg N (chambers 4-6). In conjuction with the automatic sampling system for N2O, manual samples were taken using sample ports inserted into the existing sampling lines. Immediately after the end of each chambers automated sampling cycle, 10ml samples were collected for determination of 15N-N2O and 15N-N2 via mass spectrometry. Samples were taken daily for the inital week, then twice daily, weekly and fortnightly for 80 days following the labelled fertiliser application.
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