[Contribution of simulated nitrogen deposition to forest soil acidification in area with high sulfur deposition].

The impacts of nitrogen deposition on a typical acidified soil under a masson pine (Pinus massoniana) forest at Tieshanping, Chongqing in Southwest China was studied through field experiments. The changes of soil water chemistry in different layers within one year after the spray of NH4NO3 and NaNO3 solution respectively [with the same nitrogen dose of 40 kg x (hm2 x a)(-1)] indicated that although the pH value decreased a little (treated by NH4NO3) or even increased somewhat (treated by NaNO3), the concentration of base cations, i.e. Ca2+ and Mg2+, and Al3+ increased remarkably, with the Al3+ to base cation (sum of Ca2+, Mg2+ and K+) molar ratio increased from 0.5 of the reference to around or even higher than 1.0, which means Al3+ might do harm to the vegetation. The enhanced leaching of base cations and activation of toxic Al3+ both indicated the deterioration of soil acidification. In addition, the nitrogen saturation occurred with the increasing NO3- leaching. Since it was detected that NH4+ had more effect on soil acidification and eutrophication than NO3- with the same equivalence, ammonia (NH3) emission abatement should be possibly preferred to nitrogen oxides (NO(x)) for nitrogen deposition control in China.