In 1993 a field experiment was conducted to determine the influence of seeding date on flowering and seed production of velvetleaf at Kyushu National Agricultural Experiment Station, Nishigoshi, Kumamoto, on thick high humic Andosols (Melanudands). Velvetleaf seeds were seeded monthly from April to November in plots fertilized in advance at 1kg N, 1kg P2O5 and 1kg K2O/a with a compound fertilizer. Flowering and seed production of the emerged plants were evaluated. Flowering was observed in the April to August seeded plants and mature seed production in the April to July seeded ones. Days from seeding to first flowering, plant height and plant age in leaf number, and days from seeding to initiation of the production of mature capsules were decreased with the later seeding dates, and both flowering and seed production showed short-day photoperiodic response. The number of seeds produced per plant ranged from 2,214 in the April seeded plants to 424 in the July seeded. Weights of 100 seeds ranged from 866mg in the plants in the May seeding to 993mg in those in the July seeding, and the seeds produced by the plants seeded in April and July were heavier than those seeded in May and August. Thus, in Kyushu, velvetleaf emerging from April to July was able to efficiently produce vigorous seeds due to the short-day photoperiodic response, and plants emerging in April might cause the most serious problem by producing a large amount of seeds.

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In the Kyushu region of Japan, mixed seeding cultivation of corn and sorghum is promising as a labor‐saving cropping system that makes effective use of forage crop fields in the summer season. In this study, we tested a few levels of seeding rates of a sorghum‐sudangrass hybrid (SSH) in a mixed seeding with corn planted at the standard rate (6.67 plants m−2) under a partial tillage condition in fields where Italian ryegrass had been sown after manure application and its second crop had been harvested. Our results indicate that the appropriate seeding rate of SSH with corn under partial tillage to maximize both the corn yield in the first crop and the annual yield is 1 g m−2, irrespective of the manure application levels. At this rate, the annual yield from the mixed‐seeded plots of corn and SSH was 20% higher than that from plots on which corn was seeded alone.

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