Short-term waterlogging often occurs in upland fields converted from paddies in Japan, since paddy fields have poor surface drainage and a high water table. Many previous studies have reported on relatively long-term waterlogging effect on soybean (Glycine max), however there were few studies for short-term waterlogging effect.

   The objective of this study was to clarify the effects of different durations of waterlogging (W) and waterlogging with soil reduction (WR) on soybean nitrogen fixation at different soil temperatures.   The acetylene reduction activity (ARA), stomatal conductance (SC), nodule dry weight and nitrogen contents were measured.

   The ARA under the W treatment for 3, 5 and 7 days (d) was restored to the same level as in the control (C) at 3 days after treatment (DAT). However, it did not restored under the WR treatment for 3, 5 and 7 d in a greenhouse experiment. In the experiments under three soil temperature conditions (lower than 30 oC, around 34 oC and higher than 36 oC) and with two waterlogging durations (3 and 5d) in the growth chamber,  ARA under the W treatment was restored after the treatment irrespective of soil temperature and waterlogging duration whereas ARA under the WR treatment was restored only after the short waterlogging at a low soil temperature.

  We concluded that the recovery of nodule nitrogen fixation after waterlogging is strongly affected by the degree of reduction and temperature of the soil.