High nitrogen deposition in an agricultural ecosystem of Shaanxi, China

Atmospheric nitrogen (N) deposition plays an important role in the global N cycle. Data for dry and wet N deposition in agricultural ecosystem of Shaanxi in China is still imperfect; in this study, we continuously measured concentrations and fluxes of dry N deposition from 2010 to 2013 in Yangling district of Shaanxi province and wet N deposition from 2010 to 2012. The average annual concentrations of NH 3 , NO 2 , HNO 3 , particulate ammonium, and nitrate (pNH 4 + and pNO 3 − ) varied among 3.9–9.1, 6.6–8.0, 1.2–1.4, 3.1–4.3, and 3.3–4.8 μg N m −3 , respectively, with mean values of 6.0, 7.2, 1.3, 3.8, and 4.1 μg N m −3 , respectively, during the entire monitoring period. The annual NH 4 + -N and NO 3 − -N concentrations in precipitation ranged 3.9-4.3 and 2.8-3.4 mg N L −1 with the mean values of 4.1 and 3.3 mg N L −1 . The NH 4 + -N/NO 3 − -N ratio in rainfall averaged 1.2. Dry N deposition flux was determined to be 19.2 kg N ha −1 year −1 and the wet N deposition flux was 27.2 kg N ha −1 year −1 . The amount of total atmospheric N deposition (dry plus wet) reached 46.4 kg N ha −1 year −1 , in which dry deposition accounted 41 %. Gaseous N deposition comprised over 75 % of the dry deposition, and the proportion of oxidized N in dry deposition was equal to the reduced N. Therefore, the results suggest that more stringent regional air pollution control policies are required in the target area and that N deposition is an important nutrient resource from the atmosphere that must be taken into consideration in nutrient management planning of agricultural ecosystems.