1. Forms and Amount of Nitrogen in Soil; Wen Qi-xiao. 2. Natural 15N Abundance in Soils; Xing Guang-xi, et al. 3. Mineralization of Soil Nitrogen; Zhu Zhao-liang. 4. Fixation and Release of Ammonium; Wen Qi-xiao, Cheng Li-Li. 5. Adsorption and Diffusion of Ammonium in Soils;...