Soil acidification in croplands in China is known to be caused by excessive application of nitrogen (N) fertilizers and high rate of acid atmospheric deposition, especially in red soil regions of Southern China. A systematic overview of the long term impacts of fertilizer management, climate and soil properties on yields, nitrogen use efficiency and soil acidification rates is, however, lacking. The main aim of the proposed research is to assess N use efficiencies and soil acidification rates at 19 long term experimental plots in southern China as a function of N fertilizer rate and fertilizer type (inorganic NPK fertilizer versus organic manure) for different combinations of crop, climate and soil properties. In addition, a soil acidification model will be used to predict impacts of different manure, fertilizer and lime combinations on soil acidification at those plots and to assess the best ratio of manure, fertilizer and lime to counteract acidification in the experimental plots and for different regions of Southern China.