Nitrogen deposition and its contribution to nutrient inputs to intensively managed agricultural ecosystems.

Interest in nitrogen inputs via atmospheric deposition to agricultural ecosystems has increased recently, especially on the North China Plain because of extremely intensive agricultural systems and rapid urbanization in this region. Nitrogen deposition may make a significant contribution to crop N requirements but may also impose a considerable nutrient burden on the environment in general. We quantified total N deposition at two locations, Dongbeiwang near Beijing and Quzhou in Hebei province, over a two-year period from 2005 to 2007 using an 15N tracer method, the integrated total N input (ITNI) system. Total airborne N inputs to a maize wheat rotation system at both locations ranged from 99 to 117 kg N x ha(-1) x yr(-1), with higher N deposition during the maize season (57-66 kg N/ha) than the wheat season (42-51 kg N/ha). Plant available N from deposition for maize and wheat was about 52 kg N x ha(-1) x yr(-1), accounting for 50% of the total N deposition or 31% of total N uptake by the two crop species. In addition, a correction factor was derived for the maize season to adjust values obtained from small pots (0.057 m2) compared with field trays (0.98 m2) because of higher plant density in the pots. The results indicate that atmospheric N deposition is a very important N input and must be taken into account when calculating nutrient budgets in very intensively managed agricultural ecosystems.