An experiment was conducted aiming to estimate the variability of viable seeds of red rice (Oryza sativa L.) in soil under three rice (O. sativa L.) seeding systems: conventional, no-tillage and water seeded. It was located in São Borja, Rio Grande do Sul state, Brazil, in an albaqualf soil with an average of 150 red rice plants per square meter before establishing the experiment. In order to estimate the seed bank, soil samples were colected using a cylinder with 10cm diameter. Twelve samples were obtained in each plot at two soil depths (0-1cm and 1-10cm) and the seeds were submited to the tetrazolium test to assess its viability. The experiment was a bifatorial in a randomized block design with three replications, in which seeding systems were the main effect and sampling depth the secondary factor. The results indicated a greater number of viable red rice seeds under conventional system (1,994 seeds m²), intermediate values for the no-tillage system (597 seeds m²), and lower numbers under the water-seeded system (93 seeds m²). Therefore, it was demonstrated that rice seeded in water-seeded system favors control of red rice, mantaining the quantity of red rice seeds in lower densities than under the conventinal or no-tillage systems.
weeds; seed viability; lowland management
