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Estimating nitrogen losses from furrow irrigated cotton rotation systems. Dalby, Queensland, 2005-2006 [GCRC]
Dr.
David
Rowlings
Institute for Sustainable Resources, Queensland University of Technology
Principal Investigator
Gardens Point campus, 2 George St
Brisbane
Queensland
4001
Australia
+61 7 3138 7636
d.rowlings@qut.edu.au
Professor
Peter
Grace
Institute for Sustainable Resources, Queensland University of Technology
Director ISR
2 George St
Brisbane
Queensland
4001
Australia
+61 7 3138 9283
pr.grace@qut.edu.au
Ms.
Siobhann
McCafferty
Institute for Future Environments, Queensland University of Technology
Data Librarian
2 George Street
Brisbane
QLD
4000
Australia
+61 7 3138 0457
siobhann.mccafferty@qut.edu.au
Custodian/Steward
Cotton is one of many agricultural industries 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, nitrate leaching which contribute to environmental pollution. The inefficient use of fertiliser applied nitrogen also reduces profitability.
Irrigated cotton grown on alkaline grey clay soils often use nitrogen fertilizer inefficiently, due largely to nitrogen loss (commonly 50 - 100 kg N ha-1) through denitrification. These and the heavier black clays (Vertosols) are the dominant soils in the cotton growing region of Australia and with their high water holding capacity are ideal environments for denitrification and associated losses of nitrous oxide (N2O) and N2. The nitrogen gases emitted also include ammonia, but it is N2O, a potent greenhouse gas with a Global Warming Potential (GWP) approximately 300 times that of carbon dioxide (CO2), which has fuelled debate.
Field measurements using a portable automated gas analysis system were carried out on a typical furrow irrigated cotton farm near Dalby on Queenslands Darling Downs over the 2005/06 season. The impact of water run applications of fertiliser N on emissions were examined with half (three) the chambers placed within the irrigation furrow and the remaining three (with 50 cm extentions) placed over growing plants in the row .
Cotton
Furrow irrigated
Alkaline grey clay soils
N2O
Nitrous oxide
CO2
Vertosol
Auto Chambers
Dalby
QLD
0502
anzsrc-for
Permission required from data owner
2005-10-18
2006-04-16
Dalby, Queensland
151.28
151.28
-27.17
-27.17
1303264744571
Automatic Chamber
For determination of soil borne CH4, N2O and CO2 fluxes an automated gas sampling system was utilized, similar to the one described in detail by Breuer et al. (2000) and Kiese et al. (2003)
This system consisted of pneumatically operated static chambers (non-steady-state, non-through-flow), linked to an automated sampling system and a gas chromatograph. The clear acrylic glass chambers covered a surface area of 0.25 m2 (500 mm x 500 mm) with a height of 150 mm and were secured to stainless steel bases inserted permanently into the soil to a depth of 100 mm. In the row, chambers covering plants were increased in height incrementatlly as the crop grew from 150mm, to 450 mm to 650mm.
A transparent tinted plastic coating was placed on the lids to reduce heat build-up within the chambers when closed. A tipping bucket rain gauge (Davis Instruments Corp. CA, USA) connected to the system allowed for automated opening of the lids during rainfall events.
Greenhouse Gas Flux Measurement
Nitrous oxide and CH4 concentrations were determined using a gas chromatograph (SRI GC8610, Torrance, CA, USA) equipped with 63Ni Electron Capture Detector for N2O and a Flame Ionisation Detector for CH4. Carbon dioxide was measured continuously with a non dispersive infrared CO2 analyser (LI-820; LI-COR, Lincoln Nebraska, USA). To minimize interference from moisture vapour and CO2 on N2O measurement, a precolumn filled with sodium hydroxide coated silica was installed ahead of the analytical column and changed regularly.
A full measurement cycle for flux determination commenced with lid closure and finished when the lids opened 96 minutes later. The lids remained open for a further 96 minutes before the commencement of the next cycle, allowing 7 or 8 cycles per day. Fluxes of N2O, CH4 and CO2 were calculated from the slope of the linear increase or decrease in concentrations within the chambers over the closure time.
Flux rates were discarded if the r2 was <0.81 for N2O and CH4 and <0.90 for CO2. The flux rate was then calculated and corrected for air temperature during measurement and site pressure using the procedure outline by Barton et. al. (2008).
Gas chromatograph (SRI GC8610, Torrance, CA, USA) equipped with 63Ni Electron Capture Detector for N2O and a Flame Ionisation Detector for CH4.
Non dispersive infrared CO2 analyser (LI-820; LI-COR, Lincoln Nebraska, USA).
Water Content and Soil Temperature
A FDR (EnviroSCAN Sentek, Stepney, South Australia) moisture probe located centrally to the chambers within both the row and furrow. This recorded half-hourly readings of volumetric water content (5-10 cm) while soil temperature (10 cm) was measured at 30 minute intervals (PT100).
A FDR moisture probe (EnviroSCAN Sentek, Stepney, South Australia).
Climate Data Collection
For climate data an automatic weather station (Davis Instruments Corp. CA, USA) installed nearby recorded half-hourly rainfall, temperature, relative humidity and wind speed and direction values
Automatic weather station (Davis Instruments Corp. CA, USA)
18/10/2005 to 16/04/2006
Darling Downs (near Dalby), Southern Queensland, Australia.
Three replicate sampling chambers were placed the in the irrigation furrow and three in an adjacent row.
Chambers were placed within the same row/furrow over a 10 metres long strip within the larger cotton field, approximately 15 m from the irrigation head-ditch.
92 kg of N was applied prior to planting on the 10/08/2005 (anhydrous ammonia) and a further 70 kg 3 weeks later. Planting occured on the 2/11/2005 and a further 30 kg N applied as water run anhydrous on the 26/01/2005 and 15 kg n on the 24/02/2006 applied using using the same method.