Nitrous oxide emission factors for fertiliser ammonium sulphate, diammonium phosphate, and urea

This study determined the nitrous oxide emission factors (EF1, the percentage of N2O emitted as a proportion of fertiliser N applied) for fertilisers ammonium sulphate (AS), diammonium phosphate (DAP), and urea under the same field conditions. Trials were conducted on pasture soils across four sites (Waikato, Manawatu, Canterbury and Otago) in New Zealand during late autumn and spring of 2022. The average EF1 values for urea across all four sites were 0.128% (95% C.I., 0.023% and 0.249%) in late autumn and 0.136% (95% C.I., 0.031% and 0.259%) in spring. The corresponding EF1 values for AS were 0.125% (95% C.I., – 0.021% and 0.246%) in late autumn and 0.083% (95% C.I., 0.015% and 0.197%) in spring, while for DAP, they were 0.049% (95% C.I., – 0.044% and 0.157%) in late autumn and 0.090% (95% C.I., -0.009% and 0.205%) in spring. The mean EF1 values across all four sites and two seasons were calculated as 0.132% (95% C.I., 0.016% and 0.269%) for urea, 0.104% (95% C.I., – 0.008% and 0.235%) for AS, and 0.069% (95% C.I., – 0.036 and 0.194) for DAP. No significant differences in EF1 were observed between the three fertilisers (P > 0.05) at individual sites or when considering all four sites collectively.