Contribution of dissolved organic nitrogen deposition to total dissolved nitrogen deposition under intensive agricultural activities

For elucidating the atmospheric deposition contribution of dissolved organic nitrogen (DON) to the total dissolved nitrogen (TDN) deposition rate, dissolved inorganic nitrogen (DIN: NH4+ + NO3-) and DON deposition rates were annually and monthly estimated during 4 and half-yr monitoring period in an experimental multi-farm under intensive agricultural activities of N fertilizer use and animal husbandry in Central Japan. Annual NH4+, DON and NO3- deposition rates in bulk and wet deposition data accounted for 48%, 32% and 20% of TDN deposition, respectively, which indicated that this area is strongly affected by the intensive agricultural activities. The DIN and DON deposition rates were respectively estimated at 21.6 and 10.1 kg N ha(-1) yr(-1), which ranked high in a worldwide regional data set. Consequently, this area has been exposed to a large amount of N deposition including DON with N fertilizer input. The difference between bulk and wet deposition rates (NH4+ and DON) is one of important factors controlling the N deposition in this area. Monthly DON deposition showed positive correlations with DIN and NH4+ deposition rates, respectively, with a significant linear regression curve. The linear regression curve of our monthly data (n = 127) indicates the same trend as the worldwide annual data set (n = 31).