Ammonia volatilisation following urea fertilisation in an irrigated sorghum crop in Italy

•Ammonia fluxes were measured with three inverse modelling approaches.•The three approaches agreed within 20%.•Ammonia emission increased sharply after each water supply by irrigation or rain.•Ammonia emission mainly originated from soil.•Ammonia losses reach 10% (14%) of the total applied nitrogen in 8 days (20 days). Ammonia (NH3) fluxes were estimated by three inverse modelling methods over a sorghum field following the application of 240kgNha−1 of urea pills under a semi-arid Mediterranean climate. Ammonia volatilisation started following irrigation, which coincided with the third urea application. The maximum volatilisation rate was reached 7 days after irrigation. A clear dependence of the NH3 volatilisation on irrigation and rainfall events was observed. The NH3 fluxes ranged from −2.5 to 45μgNH3m−2s−1. The canopy compensation point jumped from 9μgNH3m−3 before urea hydrolysis to 131μgNH3m−3 afterwards, while the soil compensation point varied in the meantime from 24 to 800μgNH3m−3 on average. The soil-dominated observed NH3 emissions were reasonably well reproduced by a two-layer resistance model. Overall, between 10% and 14% of the total nitrogen applied was volatilised.