Effects of excessive soil moisture on photosynthesis and nitrogen metabolism.

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1. The first purpose of this experiment was to examine whether the application of nitrogen (N) fertilizer as ammonium sulfate is effective as a countermeasure against excess moisture injury to soybeans[Glycine max (L.) Merr. ]. Soybeans (C. V. Tamahomare) were grown in an upland field converted from paddy. Flooding treatment was conducted in the furrows to a depth of 5 to 8 cm for 10 days at flower-bud differentiation stage and subsequently fertilizer was applied at 12g N per m^2.In the non-flooding plot, seed yield did not increased due to the supplemental- N, however in the flooding plot, it was increased by about 20%. The increase in seed yield was brought about the increase in the number of pods.2. The second purpose of this experiment was to examine how the number of pods increased due to the supplemental N. At the flower-bud differentiation stage, soybean plants cultivated in pots were treated with tree soil moisture conditions for 7 days : excess moisture (water table of 5 to 7. cm below the soil surface), flooding (water table of 2 to 3 cm above the soil surface) and control, and subsequently ammonium sulfate was applied at 5g per pot.In the excess moisture and flooding plots without the supplemental N, the total number of nodes per plant and the number of pods per node decreased. The resultant decrease in. the number of pods brought about decrease in seed yield. However, in those plots with the supplemental N, the number of pods per node increased and the resultant increase of the number of pods brought about increase in seed yield. It was assumed that increase in the number of pods per node was attributed to increase in photosynthetic rate.