Biological processes in agro-ecosystems have been affected by atmospheric nitrogen (N) deposition, but there is uncertain of the N deposition fluxes and associated variations. This study aimed to characterize the atmospheric inorganic N (AIN) in wet deposition to a typical red soil farmland at the Red Soil Ecological Experiment Station, Chinese Academy of Sciences in Southeast China. We collected rain samples using an ASP-2 sampler at a 4-week interval, recorded rainfall and rain frequency by an auto-meteorological experiment sub-station and determined NO (3) (-) - and NH (4) (+) -N levels in precipitation with an AutoAnalyzer 3 for five continuous years (2005-2009). Precipitation-weighted concentrations of NO (3) (-) - and NH (4) (+) -N ranged from 0.02 to 0.17 mg L-1 month(-1) N and 0.05 to 0.42 mg L-1 month(-1) N, respectively. Wet AIN deposition fluxes substantially varied with season. The highest AIN level was found in spring (March to May) with the average of 11.3 kg ha(-1) season(-1) N, which was significantly higher than that in autumn and winter (p < 0.01). Annual AIN fluxes ranged from 26.4 to 39.0 kg ha(-1) a(-1) N, which approached to the critical loads. The NH (4) (+) -N deposition fluxes varied from 17.4 to 27.0 kg ha(-1) a(-1) N, accounting for 65.8-71.5% of annual AIN deposition fluxes, whereas the AIN fluxes in the rainy season (April to June) ranged from 5.0 to 20.2 kg ha(-1) a(-1) N, accounting for 17.6-51.9% of annual AIN deposition fluxes. Wet inorganic N deposition has intensively been influenced by human activities, particularly agricultural activities, and would increase potential ecological risk in the red soil agricultural ecosystem. Our results suggest that wet N deposition to red soil farmlands, particularly in the rainy season should not be neglected.
