In tobacco-rice sequential cropping system, a field experiment on effect of different ratio of NO3ˉ-N to NH4^+- N on growth and quality of flue-cured tobacco and transformation of nitrogen fertilizer in tobacoo growing season was conducted with K326 as material in Hunan Agricultural University in 2007. The results showed that the content of NO3ˉ- N in the 0-20 cm soil layer showed a decreased trend during the whole growth duration of tobacco. It was beneficial to growth of tobacco in early and middle growing period of flue-cured tobacco in 1...