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  • Title: Improved prediction of farm nitrous oxide emission through an understanding of the interaction among climate extremes, soil nitrogen dynamics and irrigation water.
    Author: Maraseni T, Kodur S.
    Journal: J Environ Manage; 2019 Oct 15; 248():109278. PubMed ID: 31336339.
    Abstract:
    Reducing nitrous oxide (N2O) emissions from agriculture soils is crucial, as it accounts for 5.6-6.8% of global anthropogenic emissions. This study aims to understand the interaction among climate, soil nitrogen (N) and applied N on N2O emissions from the irrigated cotton farming system and its implications on farm economics. We conducted simulations for 116 years (1900-2015) and assessed the effect of different N-fertiliser application rates, initial soil nitrate (NO3) N levels and rainfall conditions on N2O emissions, N2O emission factors (EFs) and financial returns (with and without N2O costs). Results showed the following. 1) The proportional impact of higher N fertiliser rates on soil N2O emissions was greater when initial soil N level was lower (5 mg NO3 kg-1) than higher (35 mg NO3 kg-1). However, the volume of impact was greater under higher initial soil N levels. 2) The relationship between N fertiliser rates and the EFs (range 0.03-7.2%) was not linear but bell-shaped. 3) Fertiliser N requirements increased with rainfall and decreased with initial soil N. Accordingly, the cotton returns for the driest rainfall condition (<10th percentile) were maximum at 300, 250 and 150 kg N ha-1 for initial soil N of 5, 20 and 35 mg NO3 kg-1. For the wettest rainfall condition (>90th percentile), these rates were 50 kg ha-1 higher across the initial soil N conditions. Any additional application of N-fertiliser above these rates was counterproductive. 4) Inclusion of N2O cost into farm economics reduced the annual returns by up to $39 ha-1, but the optimal fertiliser application rates remain the same. 5) Optimising N fertiliser rates to soil N and rainfall conditions increased the annual returns by up to $303 ha-1, with a further increase of $15 ha-1 from fertiliser use efficiency when the Australian Government incentives under the $2.55 billion dollar Emission Reduction Fund program was considered. These findings suggest that N-fertiliser application rates and N2O emission mitigation strategies need further refinements specific to prevailing soil and climate variabilities.
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