Alternative N application strategies for reduced N2O emissions in flood-furrow irrigated cotton

Graeme Schwenke1, Annabelle Mcpherson2

1 NSW Department of Primary Industries, 4 Marsden Park Road, Tamworth, NSW, 2340, www.dpi.nsw.gov.au, Email [email protected]

2 NSW Department of Primary Industries, 4 Marsden Park Road, Tamworth, NSW, 2340, www.dpi.nsw.gov.au, Email [email protected].au

Abstract

The large inputs of N fertiliser needed for high-yielding irrigated cotton can potentially lead to substantial emissions of the greenhouse gas, nitrous oxide (N2O). We compared the impact on N2O emissions of three alternative strategies for applying the required amount of N to a commercial flood-furrow irrigated cotton crop. Compared to applying all N fertiliser pre-sowing, splitting the application between pre-sowing and in-season applications led to temporal differences in the N2O emitted, but there was no cumulative difference over the whole season. Similarly, altering the placement of the pre-sowing N fertiliser band from the non-irrigated side of the hill to the irrigated side of the hill led to a spatial difference in the N2O emission pattern, but no cumulative effect was observed. Almost all N2O emissions occurred in response to the first three of eight irrigation events, with the emissions after the second and third irrigations only observed where additional N was applied as water-run urea. The mostly low-intensity rainfall during this growing season had little impact on N2O emitted. Future research should focus on minimising N2O losses from the first irrigation, either through further reducing pre-plant N rates or by using a nitrification inhibitor with the pre-plant N application.