Abstract
The purpose of this experiment was to examine whether the application of nitrogen (N) fertilizer as ammonium sulfate is an effective countermeasure against excess moisture injury of soybeans [Glycine maz (L.) Merr.]. Soybeans (cv. Tamahomare) were grown in an upland field converted from paddy. Flooding treatment was conducted in furrows to a depth of 5 to 8 cm for 8∼11 days at flower-bud differentiation stage and subsequently fertilizer was applied at the rate of 12 g N per m2. In the flooding plot without supplemental N, seed yield decreased by 20% ; however, in the flooding plot with supplemental N, seed yield decreased only by 6%, since the decreases in pod number were low. The reasons for the low reduction in pod munber were examined in a pot-cultured experiment. Plants under excessive soil moisture and without supplemental N had low N content in the leaf blade which brought about a marked decrease in the photosynthetic rate. In contrast, supplemental N increased the N content in the leaf blade and photosynthetic rate. It was assumed that the increased photosynthetic rate by supplemental N inhibited bud, flower and pod shedding.
