The use of open-path FTIR techniques to measure nitrous oxide, ammonia, and methane emissions from a sugarcane farm in Australia

Intensive agricultural systems are a main source of greenhouse gas (GHG) emissions. The nitrogen (N) fertilizers that are applied to crops to increase crop productions during growing season can lose approximately half of the applied N to the atmosphere as nitrous oxide (N₂O) and ammonia (NH₃).This results in growers’ financial losses and can cause environmental pollutions. Quantification of gas emissions not only helps to develop inventories of regional and national emissions but also to improve management practices to mitigate the emissions. However, accurate quantification of the gas emissions at farm scale is challenging as the natural reactive ammonia gas is a “sticky” gas, and N₂O has spatialand temporal variability. There is a need of proper techniques to continually measure a suite of gases including N₂O and NH₃simultaneously to reduce the complexity of using multiple gas sensors for measurements.

A trial was conducted in July 2024 to measure N₂O, NH₃, and CH₄emissions following the fertilizer and fertilizer inhibitor applications at a commercial sugarcane farm in Queensland, Australia. Two separate plots were chosen, one plot was for a control plot with urea fertilizer and the second one was for the treatment plot applying urea and urea inhibitor. At each plot, a slant-path Fourier transform infrared spectrometer (slant-path FTIR) was deployed to measure a suite of gas concentrations for three weeks, including N₂O, NH₃, and CH₄, simultaneously.Thirty-min averaged wind statistics and the coordinates of locations of equipment and experimental plots were collected. These measurements of gas concentration and wind statistics were used to calculate gas fluxes using a micrometeorological technique. The fluxes of N₂O, NH₃, and CH₄from control and treatment plots showed that the effects of inhibitor on reduction of N₂O and CH₄ emissions were significant over the measurement period but NH₃ flux reduction was only triggered by the irrigation event.