Persistence of 2,4-D and glyphosate in a Cerrado soil, Brazil

The state of Mato Grosso is the main grain producer in Brazil, and weeds occurrence remains the major obstacle in the production of these grains, also increasing herbicide consumption. The aim of this study was to assess 2, 4-dichlorophenoxyacetic acid and Glyphosate (N-phosphonomethyl-glycine) herbicides mixture persistence in soybeans of Ultisol in the Brazilian Cerrado. The study was conducted in a greenhouse with randomized blocks experimental design consisting of 6x5 factorial, six application periods (0, 3, 5, 7, 10 and 14 days before sowing), five herbicide doses (0, 750 , 1500, 2250 and 3000 g ia. ha-1) and four repetitions. Herbicides were sprayed with a knapsack sprayer. Residual effect was assessed through emergence speed index (ESI), plant height, visual phytotoxicity and dry biomass of shoot and root. Results showed that, according to the decrease in the interval between herbicide application and soybean seeding, the residual effect of products was higher. As the dose increased, higher was the plant phytointoxication, influencing in the reduction of emergence speed, shoot dry matter, root dry matter and plant height, and negatively acting on crop development.   Key words: Pesticides, residual effect, sowing, soybean.