Hizbullah Jamali1, Wendy Quayle2, Clemens Scheer3, Jeff Baldock4
1 CSIRO Agriculture and Food, LMB 59, Narrabri, NSW 2390, Australia; email: firstname.lastname@example.org
2 Centre for Regional and Rural Futures, Deakin University, Griffith, NSW 2680, Australia
3 Queensland University of Technology, Brisbane, QLD 4000, Australia
4 CSIRO Agriculture and Food, PMB 2, Glen Osmond, SA 5064, Australia
Nitrous oxide (N2O) emissions derived from N fertilisers applied to agricultural soils are the largest source of N2O in Australia. In this study we tested the hypothesis that applying irrigation at a reduced deficit (RED) and splitting urea into two applications (SPLIT), would reduce N2O emissions compared with the conventional practice of applying irrigations at larger deficits (CONV) and a single in-crop urea application. CONV treatments received four irrigations of 100 mm each and RED treatments received eight irrigations of 50 mm each. Urea treatments included a single application of 280 kg N ha-1 and two applications of 140 kg N ha-1 each (SPLIT). Nitrous oxide emissions from the soil surface were measured continuously and N2O concentration in soil pore space was measured periodically at 5 cm, 30 cm, 60 cm and 90 cm depths. Differences in total N2O emissions over the season were not significant among treatments. Peaks in N2O emissions were measured following irrigations. These peaks were higher in magnitude in CONV treatments during the early season irrigations and during late season higher magnitudes were detected in RED treatments. Highest N2O concentrations were consistently measured in the top soil layer. Plant N uptake and biomass were similar among treatments. Leaching losses were small and mostly observed in cores that received 100 mm irrigations.