Clemens Scheer(A,B), David W. Rowlings(A), and Peter R. Grace(A)
A. Institute for Future Environments, Queensland University of Technology, Brisbane, Qld 4000, Australia.
B. Corresponding author. Email: [email protected]
Nitrogen (N) fertiliser is a major source of atmospheric nitrous oxide (N2O), and over recent years there has been growing evidence for a non-linear, exponential relationship between N fertiliser application rate and N2O emissions.
However, there is still a high level of uncertainty around the relationship of N fertiliser rate and N2O emissions for many cropping systems.
We conducted year-round measurements of N2O emission and lint yield in four N-rate treatments (0, 90, 180 and 270 kgNha–1) in a cotton–fallow rotation on a black vertosol in Australia.
We observed a non-linear exponential response of N2O emissions to increasing N fertiliser rates with cumulative annual N2O emissions of 0.55, 0.67, 1.07 and 1.89 kgNha–1 for the four respective N fertiliser rates, but no N response to yield occurred above 180 kgNha–1.
The annual N2O emission factors induced by N fertiliser were 0.13, 0.29 and 0.50% for the 90, 180 and 270 kgNha–1 treatments respectively, significantly lower than the IPCC Tier 1 default value of 1.0%.
This nonlinear response suggests that an exponential N2O emissions model may be more appropriate for estimating emission of N2O from soils cultivated to cotton in Australia.
It also demonstrates that improved agricultural N-management practices can be adopted in cotton to substantially reduce N2O emissions without affecting yield.
Received 20 November 2014, accepted 8 October 2015, published online 6 July 2016