Study on Rhizobium Behaviors in Low Moisture Content of Upland Soil

Abstract

Soybean seeds (8 kg.rai^-1 , rate) inoculated with Bradyrhizobium japonicum (200 g. peat carrier, 7.80 x 10⁸ cell g.^-1, peat) were sown in hot (42-45 degree C), dry (2-4% by weight) soils, at 0, 1, 3, 5, 7 and 10 days in January, 1987 and 0, 10, 15 and 20 days in February, 1988, before the first irrigation. The survival of inoculated rhizobia as estimated by YMA-plate count, showed that the number decreased every day after seed sowing but the survival was not less than 1.00 x 10⁵ cell seed^-1 even in 20 days treatment. It was also found that N₂ – fixation activity by ARA method and nodule dry weight did not too much decreased. Furthermore, the recovery of inoculated rhizobia as evaluated by fluorescent antibody technique was found in very high number over the un-inoculated plot. It could be recommended that soybean inoculated with Bradyrhizobium japonicum in dry soil under rain-fed area was able to survive at adequate number for increasing soybean yield.