In order to evaluate the effect of blue soybean (Glycine max Merr.) and rice rotation systems on rice yield and soil fertility. Field experiments were conducted with different rotation systems that blue soybean was sowed in spring, fall and winter, respectively. The results indicated that the fresh shoot weight of blue soybean in spring crop, fall crop, volunteered plants from the fall crop, and winter crop were 5.73, 5.29, 1.49 and 0.16 kg/m², respectively. The amounts of nitrogen from above green manure were 505, 590, 114 and 11 kg/ha, respectively. The rice yields were significantly increased on the treatments of sowed and incorporated of blue soybean in both spring or fall season, but no significant effect in winter season. The soil organic matters, such as P, K, Ca, Mg, Fe and Mn contents in incorporated blue soybean plots were slightly higher than those of control. Therefore, the incorporation of blue soybean may significantly increase rice yield and maintain soil fertility.

Key words: blue soybean (Glycine max Merr.), green manure, rice, soil fertility.