Abstract:An laboratory aerobic incubation and simulated leaching soil column experiment were conducted to investigate the effects of urea addition on nitrification, nitrogen (N) leaching, base cations leaching and soil/leachate acidification in four tropical and subtropical acid soils including latosols in Hainan (HR, granite, forest land), latosols in Yunnan (YR, basalt, forest land), red soil in Jiangxi (RU, quaternary red earth, upland field) and yellow-brown soil in Jiangsu (YU, quaternary Xiashu loess, upland field). The results showed that nitrifying activities in four soils were in the rank of YU>RU>YR>HR. Dissolved organic N (DON) and ammonium N (NH4+-N) were the predominant forms of N leaching, while nitrate N (NO3- -N) dominated N form of YU leachate. In YR and RU, both NO3- -N, NH4+-N and DON existed in each leachate. A significant positive linear correlation was observed between total base cations and NO3- -N in leachates. Nevertheless, leaching of each base cation varied with ionic innate qualities and soil properties. Ca2+ played a key role in both buffering H+ produced by nitrification and balancing the negative charges of leaching NO3- -N. Nitrification of exogenous NH4+-N in soil with low cation exchange capacity (CEC) and base cations saturation like RU caused not only base cation leaching but also NH4+-N and H+ leaching. Overall, urea addition might cause N leaching in a shorter time in tropical and subtropical soils and thus trigger environmental issues.