Phytoremediation of Brazilian Cerrado soil to reduce herbicide persistence using tropical grasses

Brazil has extensive areas covered in pastures with a large infestation of invasive plants. Picloram is one of the most widely used herbicides due to its residual properties in the soil. Phytoremediation is a promising technique for soil decontamination carried out by plants. The objective of this study was to investigate phytoremediation in soil from the Brazilian Cerrado biome through the cultivation of phytoremediating tropical grasses to reduce herbicide persistence. The experimental design was entirely randomized in a 4x6 factorial arrangement, corresponding to four cultivation systems (uncultivated soil, cultivated with Brachiaria decumbens, cultivated with Sorghum bicolor and cultivated with Pennisetum glaucum), and six doses (0, 2, 4, 8, 16, and 32 g i.a. L-1 ha-1) of the herbicide picloram (triethanolamine salt). The herbicide applied 48 hours before emergence (pre-emergence), resulting in 24 treatments with 4 replications. The established period for the phytoremediation species was 90 days after emergence. After 24 hours, soybean (Glycine max) was sown as a bioindicator species for the presence of picloram. Phytotoxicity, Falker® chlorophyll index, plant height and dry biomass of the aerial part and dry biomass of the roots of the phytoremediating species and the bioindicator species were evaluated and the data was submitted to analysis of variance. When significant, they were subjected to regression analysis for herbicide doses and Scott-Knott test for crop types, both with an error level of 5% probability. The tropical forage grasses showed resistance to the herbicide picloram with positive effects on phytoremediation in the analyzed variables in the bioindicators when applied at doses ranging from 2, 4 and 8 g i.a. L-1 ha-1. All the phytoremediating grasses had the potential to reduce the persistence of picloram in the soil when applied at doses within the commercial recommendation, even over a short period of 90 days.