Managing Global Resources for a Secure Future

The excess soil water and flooding are major production constrains in soybean production in Japan. Reduced leaf growth rate under excess water during early growth is one of the major aspects related to yield reduction, because it causes not only reduced crop growth rate but also weakened competitiveness with weeds and hence low crop performance in the late growth season. By pot-cluture experiments, we analyzed relative leaf growth rate of cv. Enrei under various condirions with varied depth of water table and various time/length of hight water table (5cm beneath the soil surface). The leaf growth rate responded to depth of water table rather than soil water content and a temporal flooding as short as one or two days caused a similarly serious reduction of leaf growth rate as that by continuouns flooding up to one week depending on soil temperature. The responsiveness of leaf growth to the short term flooding was assessed for divergent soybean cultivars in the field. We found that there is siginificant but limited rage of variation in the leaf growth reponse and that Japanese cultivar group is relatively less responsive to flooding than the groups of other regions.