Nitrogen Isotope Budgeting in Furrow-Irrigated Cotton, Narrabri NSW

Brief description

N15 enriched water, plant and soil samples collected during the 2014-15 cotton season as part of a project examining nitrogen losses from irrigated cotton agriculture.
Lineage: Site description:
All samples were collected from a cotton-wheat-corn-fallow rotation under minimum tillage. The site is located at the Australian Cotton Research Institute, Narrabri; and is currently managed by Gunasekhar Nachimuthu (NSW DPI) and is part of a long term carbon monitoring project run by NSW DPI.


Field Set up: Two 15N plots were established at the site. The first was 9 m2 located over a variable tension lysimeter and fertilised with 180 kg urea-N ha-1 which had 35 atom % 15N label. The second 4 m2 plot was located 15 m downstream and two rows away from the lysimeter with 180 kg Urea-N ha-1 which had 10 atom % 15N label. The final 15N enrichment of the 9 m2 and 4 m2 plots after the addition of the mid-season application was 26.8 atom % and 8 atom % 15N, respectively. The second plot was used for soil sampling because the lysimeter plot soil cannot be disturbed.
Two micro-plots (0.25 m2) were also established near the facility. Both micro-plots were fertilised with 180 kg urea-N ha-1 which had 35 atom % 15N.
Two sets of 6 flumes were installed at the down and upstream ends of the lysimeter plot.


Sample collection and analysis:
Run-off: water samples were collected 4-5 times at each of the flumes located around the lysimeter plot. This was repeated for each irrigation. Water was analysed to TN, NOx and NH4.
Runoff water volumes were measured using portable RBC flumes. Change in water head height was measured using 0.5m Odyssey Capacitance Water Level Loggers. Flow rate was calculated from changes in water head height using the manufacturer's calibration values.

Soil samples were collected at the completion of the 2014/15 cotton season by Ben Macdonald (CSIRO) and Yvonne Chang (CSIRO).

Plant samples were collected at the conclusion of each crop season, prior to defoliation. Samples were separated into different plant parts (vegetative and reproductive material).

Deep drainage (below 2m) was collected at the start and end of each cropping season from a variable tension lysimeter. The lysimeter is maintained and operated by Anthony Nadelko (CSIRO).
Samples were analysed for urea, total nitrogen (TN), ammonium (NH4-N) and nitrate and nitrite (NOx-N). DON was calculated as TN minus urea, NH4-N and NOx-N


Data processing: Data was collated by Ben Macdonald and Yvonne Chang. Data was processed in R by Yvonne Chang.