Ammonia, methane and nitrous oxide emissions from furrow irrigated cotton crops from two nitrogen fertilisers and application methods

Abstract

• Urea broadcast and fertigation were applied at a commercial irrigated cotton farm. • Gas emissions were measured by micrometeorological technique and OP-FTIR technique. • NH 3 flux from anhydrous NH 3 was 24% higher than broadcasting urea with irrigation. • Daily fluxes of CH 4 and N 2 O were both negative following both fertilisation events. Abstract Agricultural systems use nitrogen (N) fertilizers to improve crop nutrition and yield, but applied N can negatively impact the environment and human health due to the gases emitted during and after N application. There are few direct measurements of multiple gaseous emissions from N fertiliser applied to irrigated cotton farms. This study was conducted in a commercial cotton farm in NSW, Australia to measure gaseous emissions from two N fertilisation strategies (urea broadcast onto dry soil followed by irrigation, anhydrous ammonia injected into water at the main irrigation channel), with the N fertilizer rate of 27 kg N ha −1 for each application. Gas fluxes of ammonia (NH 3 ), methane (CH 4 ), and nitrous oxide (N 2 O) were measured simultaneously using an inverse-dispersion technique coupled with open-path Fourier transform infrared (OP-FTIR) spectroscopic technique, located 150 and 800 m from the input source of the irrigation water. We found that anhydrous ammonia injected into the irrigation water contributed to higher peak NH 3 emissions (0.79 ± 0.09 kg N ha −1 day −1 ) than broadcasting urea onto dry soil (-0.06 ± 0.02 kg N ha −1 day −1 ). When daily NH 3 fluxes were accumulated over 8 − 10 days, 24% of the applied N was lost as NH 3 during anhydrous ammonia application, but no N loss was detected over the course of measurement period from the broadcast urea followed by irrigation. The daily fluxes of CH 4 and N 2 O were both negative following both fertilisation events. Our study suggests that cotton farm managers should avoid the use of anhydrous NH 3 in irrigation water to mitigate the environmental impact, as well as low efficiency of N fertiliser use.