To increase Japanese soybean yield, both practical and genetic improvements are needed. Early sowing improved yields in the United States, where indeterminate cultivars may produce better yields than determinate cultivars, particularly with early sowing. However, the mechanism for the yield response is not fully understood. Furthermore, whether these results are valid for cool regions in northern Japan is unknown. This study tested the effects of early sowing on yield and its attributes in three years using a Japanese determinate cultivar (Ryuhou) and three indeterminate cultivars (Karikei-881 and Karikei-879, recombinant inbred lines from determinate× indeterminate crosses; UA4910, a high-yield American cultivar). The effects of early sowing varied among the years. Early sowing significantly increased pod number and seed yield by increasing cumulative intercepted solar radiation (thus, growth during early reproductive stages) in years with high precipitation during mid-season (July and August). High precipitation potentially inhibited canopy development from vegetative to early reproductive stages more strongly in normally sown plants than in early sown plants. In contrast, no significant effect of early sowing was observed in a year with low precipitation during mid-season, when low precipitation during vegetative stage promoted canopy development in both sowing dates. Therefore, early sowing could escape from excess water stress and ameliorate canopy development and thereby seed yield in this region. There was no significant sowing date× cultivar interaction for seed yield in any year; thus, the indeterminate cultivars did not benefit more from early sowing in northern Japan. UA4910 had greater seed yield than Ryuhou owing to its longer growth duration and greater aboveground biomass and pod number; Karikei-881, Karikei-879, and Ryuhou showed similar seed yields. Thus, indeterminate cultivars did not necessarily have higher yields in northern Japan. These results suggest that early sowing could be effective for increasing soybean yield in northern Japan.

中文翻译：

---

早播对日本北部凉爽地区确定和不确定大豆（Glycine max (L.) Merr.）品种生长和产量的影响

为了提高日本大豆产量，需要进行实际和遗传改良。在美国，早播提高了产量，在美国，不确定的品种可能比确定的品种产生更好的产量，尤其是早播。然而，产量响应的机制尚不完全清楚。此外，这些结果是否适用于日本北部的凉爽地区尚不清楚。本研究使用日本确定品种 (Ryuhou) 和三个不确定品种（Karikei-881 和 Karikei-879，确定×不确定杂交的重组自交系；UA4910，高-产量美国品种）。早播的效果因年份而异。在季节中期（7 月和 8 月）降水量大的年份，早播通过增加累积截获的太阳辐射（因此，在早期繁殖阶段的生长）显着增加了豆荚数和种子产量。在正常播种的植物中，高降水可能比早期播种的植物更强烈地抑制了从营养阶段到早期繁殖阶段的冠层发育。相比之下，在中季降水少的年份没有观察到早播的显着影响，因为营养阶段的低降水促进了两个播种日期的冠层发育。因此，早播可以避免过度的水分胁迫，改善冠层发育，从而改善该地区的种子产量。任何年份的种子产量均无显着的播期×品种交互作用；因此，不确定的栽培品种并没有从日本北部的早期播种中获益更多。UA4910 的种子产量比 Ryuhou 更高，因为它的生长时间更长，地上生物量和豆荚数更大；Karikei-881、Karikei-879 和 Ryuhou 的种子产量相似。因此，不确定的栽培品种在日本北部不一定有更高的产量。这些结果表明，早播可有效提高日本北部的大豆产量。