The use of slant-path FTIR techniques to measure gaseous N loss in Australian dryland wheat following urea/urease inhibitors fertilizers application

Nitrogen losses following fertilizer application not only cause nutrient loss to the crops, but also have negative environmental impacts, including ammonia (NH₃) and greenhouse gas emissions (GHG) (e.g., nitrous oxide, N₂O). Numerous studies have been carried out to investigate the efficiency of fertilizer use, aiming to increase crop yield and reduce environmental impacts including GHG and other gaseous emissions. There are different measurement approaches of quantifying gaseous nitrogen (N) losses, and static chamber methods are the most commonly used approach for directly measuring emissions from soils. However, chambers interfere with the soil environment, the small measurement footprint of chambers is unable to represent the large source area and are poorly suited for long-term measurements. Here, we demonstrated the use of slant-path Fourier transform infrared spectroscopic (FTIR) technique to continually measure NH₃ and N₂O emission rates from wheat crops for 4 weeks following fertilizer application. The study was conducted in a wheat farm in Victoria, Australia in winter season in August 2025. Urea with (treatment) and without (control) a urease inhibitor was applied to the wheat crop at a rate of 98 kg N/ha. Line-averaged concentrations of NH₃ and N₂O from each plot were continually measured with vertically separated measurement paths using an OP-FTIR and wind information was recorded by a 3-D sonic anemometer. Fifteen-min average NH₃ and N₂O emission rates were calculated based on the measured concentrations and wind information. The results showed that NH₃ emission rates increased immediately after urea was applied, with greater increase than the untreated urea. Ammonia emission rates from the urease inhibitor treatment increased in the third week following fertilization, while ammonia emission rates from the control site started decreasing. Preliminary results show that the accumulative NH₃ and N₂O emissions from the urea plot were ~3 and 1.6 times higher than that from the urease inhibitor treated plot, respectively. The higher NH₃ and N₂O emissions following non-treatment urea application highlighted the benefits of a urease inhibitor for reducing N loss under high ambient temperature and lack of rainfall for 2 weeks following fertilization. Further benefits could be achieved in N use efficiency by reducing the N application rate when using the urease inhibitor.