Basically no studies in natural condition could distinguish the impacts between N
and S deposition on soil acidification, due to the large contribution of S to the acid
deposition in China. Nevertheless, nitrogen fertilization or addition experiment
could indicate the impacts of N deposition on soil acidification directly. Due to the
increase of N fertilization, the croplands in China showed significant decline in soil
pH during 1980s–2000s (Guo et al. 2010). A 6-year N addition (as NH 4 NO 3 ) study
in N-rich lowland tropical forest of southern China demonstrated that the N application enhanced soil acidification, resulting in the depletion of base cations and the
decrease of ANC and pH in soil water (Lu et al. 2014). The result of a 7-year
doubling N addition (as NH 4 NO 3 or NaNO 3 ) experiment indicated that the added
NH 4
+ (NH 4 NO 3 treated) was almost converted to NO 3
À and leached out, thus
Fig. 8.8 H-N variation at Tieshanping from 2001 to 2013. (This figure was adapted from Yu et al.
2017c with permission by American Chemical Society)
Fig. 8.9 The relationship of H
+
N and N deposition in throughfall (a) and throughfall N input versus
N leaching in soil water (b)
170
Q. Yu and L. Duan