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

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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. NH 4 +–N, NO 3 −–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 NH 4 +–N. NH 4 +–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 NO 3 ––N, which range from 0.2 to 4 mg N L −1 (average, 0.8 mg N L −1). NH 4 +–N concentration in event-based runoff from wheat fields is much lower than that in rainfall, whereas that of NO 3 ––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 NH 4 +–N in wet deposition is prone to immobilization by the soil–crop system, whereas NO 3 ––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.