Kan khatluak chua bacteria thi mi prasitthiphap sung nai kan trung nitrogen doi itsara nai saphap mi akat lae phonruam rawang chua bacteria kap chuara vesicular-arbuscular mycorrhiza to kan charoen toepto khong kla somphong (Tetrameles nudiflora R. Br.).

Twenty-nine soil samples were collected from Sakaerat forest, and counted for the number of non-symbiotic nitrogen-fixing bacteria by dilution plant count method. The numbers of the bacteria in both dry evergreen forest and dry dipterocar forest were about 4 x 10 to the 4th power CFU/g soil. One hundred and fifty-five isolates of non-symbiotic nitrogen fixing bacteria were isolated from the soil samples. Nitrogenase activities of the isolates were examined by using acetylene reduction method. Three isolates which had the highest and most consistent nitrogenase activity (1030, 747, 619 n Mole C2H4/hr/bottle) were selected for further studies. Studies were also conducted on the effect of the selected bacteria and mycorrhizal fungi on nitrogen fixation and growth of Tetrameles nudiflora seedling. The treatments were (1) sterile soil, uninoculate; (2) sterile soil with fertilizer; (3) sterile soil with mycorrhizal inoculation; (4) sterile soil with bacteria inoculation; (5) sterile soil inoculated with both mycorrhizal fungi and bacteria and; (6) nonsterile soil inoculated with both mycorrhizal fungi and bacteria. The results showed that the nitrogenase activities of treatments inoculated with mycorrhizal fungi were higher than those of uninoculated ones and those inoculated with bacteria as well. The growth of Tetrameles nudiflora seedlings inoculated with both mycorrhizal fungi and bacteria were higher than those inoculated with bacteria and those uninoculated with the microorganism but was not significantly different from the seedling inoculated with mycorrhizal fungi. Seedling inoculated with both mycorrhizal fungi and bacteria in nonsterile soil did not show significantly higher growth than the uninoculated one.