水田転換畑

Deficiency of nitrogen is the most serious problem on the growth of soybean under excess moisture conditions. lt is well known that nodulation could recover the deficiency of nitrogen while the excess moisture injury occurred in soybean. The objective of this study is to make clear the varietal differences in the nodule growth and nitrogen fixing activity under flooding conditions. In the most cultivars which had the same number and dry weight of nodules, the nodule number and nodule dry weight decreased by 18-89% and 26-97%, respectively, by the flooding treatment. The nodule growth was recovered within 14 days after removed froM the flooding treatment in the cultivars with high resistance to flooding, like 'Akiyoshi-shirodaizu' and 'Azedaizu', whereas was not recovered in the cultivar 'Shirotae' with low resistance to flooding. The same results were also observed in leaf color (SPAD value). Moreover, the acetylene reduction activity, an indicator of nitrogen fixing activity, was higher in 'Akiyoshi-shirodaizu' than in 'Shirotae' and 'Fukuyutaka', especially in the nodules grown under flooding and at low 02 conditions. The results indicated that not only the nodule growth but also the nitrogen fixing activity and the recovery after flooding stress were superior in the cultivars with high resistance compared with those in the cultivars with low resistance to flooding.