Secondary aerenchyma formation, growth and yield of soybean plants grown under continuously flooded conditions

In order to investigate the possibility of cultivating soybeans in a flooded paddy field, we examined the secondary aerenchyma formation, growth and yield of soybean variety 'Aso aogari', which forms secondary aerenchyma well, under flooded conditions. Plants were irrigated as occasion demanded or continuously flooded up to 3 cm above the soil surface after the primary leaf expanded. The flooded plants could grow until harvest. The secondary aerenchyma was observed in the hypocotyl, tap root, adventitious roots and nodules of flooded plants in the early growth stage, and its volume increased as plants grew older, although it was rare in the irrigated plants. Hypocotyl porosity of flooded plants was higher than that of irrigated plants throughout the growth period. In the pot experiment, flooding decreased the growth and grain yield per plant. In the field experiment, however, flooded plants under dense planting had the same number of ripening pods and seeds per unit area as irrigated plants had, and grain yield was over 300 g/m². These results suggested that the variety grew until harvest under flooding forming secondary aerenchyma quickly and maintaining the ventilation system until the late growth stage. Soybean cultivation in the flooded paddy field would be feasible.