Wet deposition N and its runoff flow during wheat seasons in the Tai Lake Region, China

Interest in the study of wet deposition N continues to grow for its impact on terrestrial ecosystems. Assessing the contribution of wet deposition N to intensive croplands is significant for recommending N fertilizers and minimizing environmental hazards. NH4+–N, NO3−–N, and total N concentrations in wet deposition, seasonal deposition N fluxes, and N loads in event-based runoff were determined for four consecutive wheat seasons in the Tai Lake Region. Wet deposition N during wheat seasons ranges from 11 to 15 kg ha−1 (average, 13 kg ha−1), 61% of which is in the form of NH4+–N. NH4+–N concentrations range from 0.3 to 8.5 mg N L−1 (average, 1.7 mg N L−1), showing greater temporal variations than do those of NO3––N, which range from 0.2 to 4 mg N L−1 (average, 0.8 mg N L−1). NH4+–N concentration in event-based runoff from wheat fields is much lower than that in rainfall, whereas that of NO3––N is equal to or higher than that in rainfall. N loss through runoff reaches 1.8 kg N ha−1, accounting for 14% of wet deposition N. Results indicate that NH4+–N in wet deposition is prone to immobilization by the soil–crop system, whereas NO3––N is relatively easily lost to runoff. The contribution of 11 kg ha−1 wet deposition N should be adjusted in fertilizer N recommendations for winter wheat cultivation in this region.