Abstract: The soybean yield has been increased to 1950—2100kg/ha from 982.5kg/ha since the co mprehersive reclamation carried out on the boggy bottom and in Sanjiang Plain in1986. The techniqnes of reclamation include:(1) Irrigation and water conservancy engineering; (2) Mechanical cultivation; (3) Biological techniques, especially the introduction of so ybean breed with high abilities of photosynthesis and N-fixation. The activities of Nfixation of Bradyrhizobium japonicum, Sinorhizobium fredii and other N₂-fixers and their populations sharply increased after the reclamation. Deep plough with machines benefits activities of the microbes and the development of root system and nodulation of soybean. More 3 good breeds of G. max with high photosynthesis rate and a strain of S. fredii, Sj8855, with high N₂-fixation and tolerence the boggy bottomland and pesticide have been developed and used.

Key words: Boggy bottomland, Sinorhizobium fredii, Symbiotic association, Photosynthetic rate, Comprehensive reclamation