PERFORMANCE OF SOYBEAN CULTIVARS IN 3 SOWING DATES IN RIO-GRANDE-DO-SUL, BRAZIL

Aiming to assess the behavior of soybean cultivars (Glycine max L. Mer ril) recommended for the State of Rio Grande do Sul, Brazil, at differ ent sown dates, three experiments were carried out during three years, at four sites, with sowings in mid-October, mid-November, and mid-Dec ember. A complete randomized block design with split plots was used. T he yield of the cultivars sown in mid-December was lower than the yiel ds obtained in the remaining dates for the three cycles. Sowing in mid -October and mid-November resulted in yields that were similar for the group of early and late cultivars, while the yield from mid-November sowing date was higher than mid-October for intermediate cycle cultiva rs. The performance of cultivars of;ill three cycles was similar at a given sowing date. Average reduction in yield from plots sown in Decem ber, as compared to November, was as follows: 17.3% for early cultivar s; 17.1% for intermediate cycle cultivars; and 19.7% for late cultivar s. A similar behavior was observed for grain size, plant height, and t he insertion of lower pods. It is concluded that there is a possibilit y of sowing presently grown early cultivars from mid-October onwards a nd also that the cultivars of all three cycles show a similar yield po tential in mid-December sowings.