Ammonia volatilization in Chinese double rice-cropping systems: a 3-year field measurement in long-term fertilizer experiments

The impact of long-term fertilizer on ammonia (NH₃) volatilization in a double rice-cropping system is not well documented. A long-term fertilizer experiment in Chinese double rice-cropping systems initiated in 1990 was used in this study to evaluate the NH₃volatilization. Six fertilizer treatments were designed, including inorganic fertilizer [nitrogen and phosphorus fertilizer (NP), nitrogen and potassium fertilizer (NK), and balanced mineral fertilizer (NPK)], combined inorganic/organic fertilizers at full and reduced rate (FOM and ROM), and no fertilizer application (served as control). Ammonia volatilization fluxes were measured using a continuous airflow enclosure method during double rice growing seasons from 2007 to 2009. Results showed that the cumulative NH₃volatilizations in the fertilizer plots ranged from 12.8 to 27.3 kg N ha⁻¹for the early rice season and from 17.3 to 32.7 kg N ha⁻¹for the late rice season, which accounted for 9.2–33.6 % and 17.8–32.2 % of the applied N, respectively. The NH₄⁺concentration in floodwater is a predominant factor to NH₃losses in the double rice-cropping systems. Compared with the NPK, the cumulative NH₃volatilizations during double rice growing seasons were respectively increased by 9.7, 50.6, and 37.6 % for the NP, NK, and FOM plots, respectively, while they were decreased by 24.6 % for the ROM plots. Compared with the NPK, N uptakes by rice were decreased by 7.2–49.7 % with imbalanced fertilizer application (NP and NK), while they were increased by 9.6–41.0 % with combined inorganic/organic fertilizers application (ROM and FOM). Grain yields were comparable among the NPK, ROM, and FOM treatments, but they were declined by the treatments with imbalanced fertilizer application. These results suggested that agricultural economic viability and NH₃volatilization mitigation can be simultaneously achieved by balanced inorganic and organic fertilizers application.