Atmospheric nitrogen deposition to cropland in Fujian province, China

To quantitatively characterize atmospheric nitrogen (N) deposition in a key agricultural region, dry and bulk N deposition were measured at five sites (Fuzhou, Taining, Shanghang, Changting, and Wuyishan), in Fujian province of southeastern China over the past decade. Dry deposition of ammonia (NH3) and nitrogen dioxide (NO2) was estimated using the influential method, multiplying gaseous N concentrations by the deposition velocity simulated using the GEOS-Chem model. For bulk deposition the amounts of NH4+-N and NO3−-N were obtained by multiplying the N concentrations in rainwater by the precipitation amount. Long-term in situ observations (from 2010 to 2020) indicated that bulk N deposition decreased by 17.4 % during the monitoring period. Notably, from 2016 to 2020, total N deposition significantly decreased by 22.2 %, with an average value of 27.5 ± 1.23 kg N ha−1 yr−1. This was mostly caused by a reduction in reduced N deposition. N deposition exhibited distinct seasonal variability, determined by the amount of precipitation: dry deposition reached its peak in autumn, whereas bulk deposition was at its highest in spring and summer. The ratios of reduced to oxidized N in dry deposition, bulk deposition, and total N deposition were 3.23, 1.03, and 1.39, respectively, indicating a strong influence of agricultural sources. Our results show that atmospheric N deposition is a significant source of N to cropland and surrounding forest ecosystems in Fujian province. As such, it should be incorporated into N management strategies for crop cultivation to achieve sustainable agricultural and ecological protection.