A study on the crop ecological and agronomical factors that cause growing yield gap between Japanese and US soybean production

从气象资源、品种遗传潜力和作物管理技术的发展等方面分析了日美大豆产量差距扩大的原因。美国的气象产量极限高于日本，主要是由于太阳辐射量的增加，而美国的产量增加趋势主要是由于技术的发展。美国品种的产量始终高于日本品种，其差异主要是由于干物质生产力的差异。美国cvs表现出较高的叶片气孔导度的气体交换相比，日本cvs。这似乎是美国品种干物质生产力较高的原因。根据田间调查结果，认为遗传改良在中西部地区的贡献相对较大，而作物管理在中南部和南部地区的贡献相对较大。

The factors for the growing yield gap between Japanese and US soybean production were analyzed in reference to meteorological resources, genetic potential of cultivars and development of crop management technologies. Meteorologically determined yield limit in USA was higher in USA than in Japan by higher solar radiation, while the trend of yield increase in USA was attributed to technological development. US cultivars showed consistently greater yield than Japanese ones and the difference was resulted from different dry matter productivity. The US cvs. exhibited high leaf stomatal conductance to gas exchange as compared to Japanese cvs. and this seemed a reason for the greater dry matter productivity in the US cvs.. Based on the field surveys, it was considered that the contribution of genetic improvement was relatively greater in the midwest region, which the contribution of crop management was greater in the midsouth and south regions.