Emergence of Red Rice (Oryza sativa) Ecotypes Under Dry-Seeded Rice (Oryza sativa) Culture1

The effect of seeding depth on emergence of red rice (Oryza sativa) ecotypes from Arkansas (AR), Louisiana (LA), and Mississippi (MS) was determined under dry-seeded rice production in clay and silt loam soils in Arkansas. By 21 d after planting (DAP), all red rice ecotypes had emerged from planting depths of 1.3, 2.5, 5.0, and 7.5 cm in both clay and silt loam soils. In silt loam soil, seedling emergence from 2.5 cm 7 DAP tended to be greater than from 1.3 cm in an early (normal temperature) planting. Also in this situation, the LA ecotype emerged more vigorously than the other ecotypes at all seeding depths and emerged from 7.5 cm at levels 1.5 times those of the other ecotypes at the same depth. In the clay soil, seedling emergence from 7.5 cm at 21 DAP was greater for the LA and MS ecotypes than for the AR ecotype in an early planting, but these differences were not observed for a late (elevated temperature) planting. Seedling emergence was earlier and greater in silt loam than in clay. The LA ecotype generally produced the greatest aboveground dry matter, especially at the early planting. The MS ecotype averaged 30% less dry matter production than the AR ecotype for the late planting in both soils. The ability of the LA and MS ecotypes to emerge from greater depths than the AR ecotype under certain soil and temperature conditions suggests that they could be more difficult to control with cultural practices used in dry-seeded rice culture. Nomenclature: Red rice, Oryza sativa L. #3 ORYSA; rice, Oryza sativa L. ‘Alan’. Additional index words: Germination, red rice emergence depth, soil texture. Abbreviations: AGDM, aboveground dry matter; AR, Arkansas ecotype; DAP, days after planting; LA, Louisiana ecotype; MS, Mississippi ecotype.