A laboratory incubation study was conducted to investigate the application of crop residues with different C/N ratios and ash alkalinity content. Each component was added at 3 different rates and the potential to ameliorate soil acidity was assessed. Incorporation of crop residues was an effective method to reduce soil exchangeable acidity, Al saturation and increase base saturation, but not necessary for soil pH adjustment. The release of alkalinity from residues and the mineralization of organic nitrogen increased soil pH initially, and then decreased due to nitrifications. Various degrees of nitrification were correlated with the C/N ratios of residues. Crop residues with high C/N ratios (i.e. wheat and rice straw) repressed soil nitrification, which resulted in slight pH decrease, whereas crop residues with low C/N ratios (i.e. rapeseed cake and peanut straw) stimulated soil nitrification, and resulted in a sharp decrease in soil pH. Soil pH at the end of incubation was positively correlated with C/N ratios of residues (y = 0.003 43x + 4.14, r = 0.977). Further, a significant pH increase occurred as the rates of residues increased for residues high in C/N ratio (P<0.05), but not for residues low in C/N ratio (P>0.05). It is suggested that crop residues high in C/N ratio are preferred to ameliorate soil acidity. A further investigation is needed in the form of long-term field study on amendments variables.