The aim of this work was to evaluate the residual soil activity of the herbicide Only (imazethapyr+imazapic) to susceptible rice, cv. IRGA 417, after one or three years of Clearfield® (CL) rice cultivation. Four experiments were conducted at the Universidade Federal de Pelotas, Capão do Leão, RS, southern Brazil. The experimental design was a randomized complete block, with four or eight replications, respectively, for the two field experiments (EC1 and EC3) or the two greenhouse experiments (CV1 and CV3). The treatments were arranged as a factorial with factor A, in the same season, compared residuals per year and factor B, compared herbicide residual rates applied to CL rice. The herbicide used was Only - imazethapyr (75 g L-1) + imazapic (25 g L-1), applied at 0; 100; 150 and 200 g ha-1 with surfactant Dash added at 0.5% v/v. The herbicide was applied when CL rice was at the 3-4 leaf stage. The variables measured were aboveground dry biomass, 1000-grain weight and rice yield for experiments EC1 and EC3, and plant height, aboveground dry biomass and root dry biomass for experiments CV1 and CV3. For statistical analysis, the data were pooled together. The results showed that the CL rice system may restrict the cultivation of non-tolerant rice after CL rice. The herbicide Only at the recommended rate (100 g ha-1 ) stays in the soil long enough to affect the growth and yield of susceptible rice.
red rice; imidazolinones; soil persistence; Oryza sativa
