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 NH4–N was, on average, 2.1 times the NO3–N deposition, suggesting that reduced N is the major form of N deposition in the study area. Concentrations of NH4–N and NO3–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 NH4–N or NO3–N concentration in rainwater was observed by an exponential equation, indicating dilution of NH4–N and NO3–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.