Leaching potential of the herbicide mixture 2,4-D + picloram
Weed control strategies are fundamental to ensure pasture productivity and quality in Brazil. However, care must be taken in the use of long residual herbicides, which can increase the risk of leaching. From this context, the present study evaluates the leaching potential of the commercial mixture of herbicides 2,4-D + picloram. Leaching columns filled with loam-clay-sandy soil were used. The columns were0.6 m in length and 0.2 m in diameter. The experimental design was randomized blocks with eight replications. Treatments were arranged in a 5x2 factorial scheme, in which factor A corresponds to herbicide doses (0, 1, 2, 3 and, 4 L ha-1) and factor B corresponds to the position of herbicides in the columns (0-30 cm and 30-60 cm depth). After herbicide application, weekly rainfall of 60 mm was simulated for four weeks at the top of the columns. The columns were sectioned vertically giving rise to two section, which were separated into two portions (0-30 cm and 30-60 cm). Then, cucumber was sown as a bioindicator in the 0-30 cm and 30-60 cm layers. At 45 days after sowing, the following parameters were determined: chlorophyll a fluorescence transient, shoot length, root length, and total dry weight of plants. Both the chlorophyll fluorescence data and the biometric data of the bioindicator plant showed the presence of the commercial mixture only in the first 30 cm of depth. It is concluded that 2,4-D + picloram remained in the 0-30 cm deep layer of the loam--clay-sandy soil after 240 mm rainfall.