Nitrogen deposition in agroecosystems in the Beijing area

There is increasing interest in nitrogen (N) deposition because of its importance as a nutrient resource and a component of acid deposition within the overall global N cycle. Precipitation samples were collected for periods varying from 6 months to 6 years (1998–2004) from seven sites in the Beijing area to determine the amount and seasonal distribution of N (bulk/wet) deposition. Bulk deposition of N ranged from 26.6 to 38.5 kg N ha −1 year −1 and averaged 30.6 kg N ha −1 year −1. Bulk deposition of NH 4–N was, on average, 2.1 times the NO 3–N deposition, suggesting that reduced N is the major form of N deposition in the study area. Concentrations of NH 4–N and NO 3–N in rainfall averaged 4.8 and 2.2 mg N L −1 and showed great temporal variation from month to month. A negative relationship between rainfall and NH 4–N or NO 3–N concentration in rainwater was observed by an exponential equation, indicating dilution of NH 4–N and NO 3–N with increasing precipitation. Bulk deposition of inorganic N occurred mainly from April to September (>80% of total bulk deposition), which was consistent with both the monthly distribution of precipitation and the times of fertilizer applications in local agricultural land. Wet-only deposition of inorganic N, however, was 8.3–8.4 kg N ha −1 lower than that of bulk deposition during similar periods in 2003 (June–November) and 2004 (April–November), suggesting the potential contribution of dry deposition to total N deposition in the Beijing area.