Fitorremediação como ferramenta de sustentabilidade na produção agrícola

Abstract

The use of cover crops as a strategy for the remediation of soils contaminated with residual herbicides has emerged as a promising and sustainable alternative. Two experiments were conducted to evaluate the phytoremediation potential of different plant species grown in soils contaminated with diuron and sulfentrazone, applied individually and in combination. Experiment I was conducted under greenhouse conditions using an 8 × 3 × 3 factorial design, including the species Avena strigosa, Vicia sativa, Secale cereale, Raphanus sativus, Fagopyrum esculentum, Lolium multiflorum, Lupinus albus, and a mixture of these species. The herbicides diuron (490 g ha⁻¹), sulfentrazone (245 g ha⁻¹), and diuron + sulfentrazone (490 + 245 g ha⁻¹) were applied at three rates (untreated control, recommended rate, and twice the recommended rate). Subsequently, Cucumis sativus was sown as a bioindicator species in the soil previously cultivated with the phytoremediating species. Phytotoxicity of the phytoremediating species was assessed, together with physiological variables, including net photosynthetic rate (A, μmol m⁻² s⁻¹), stomatal conductance (gs, mol m⁻² s⁻¹), transpiration rate (E, mol H₂O m⁻² s⁻¹), intercellular CO₂ concentration (Ci, μmol mol⁻¹), water use efficiency (WUE, mol CO₂ mol H₂O⁻¹), leaf area, and shoot dry mass. For the bioindicator species, phytotoxicity, leaf area, and shoot dry mass were also evaluated. Diuron exhibited lower residual persistence, whereas sulfentrazone showed greater toxicity. The combined application of both herbicides resulted in synergistic effects depending on the phytoremediating species. L. albus, A. strigosa, R. sativus, L. multiflorum, S. cereale, and the species mixture exhibited greater tolerance and phytoremediation capacity, promoting the recovery of plant physiological activity and reducing phytotoxicity in the subsequent crop. Experiment II was conducted under field conditions to evaluate the phytoremediation potential of the same species tested in Experiment I for the remediation of soils treated with diuron (490 g ha⁻¹), sulfentrazone (245 g ha⁻¹), and diuron + sulfentrazone (490 + 245 g ha⁻¹). Sorghum bicolor and Helianthus annuus were used as bioindicator species. Phytotoxicity and shoot dry mass of the cover crops were evaluated, as well as physiological variables and grain yield components of the bioindicator species. Diuron caused lower phytotoxicity to the phytoremediating species, whereas S. cereale showed no reduction in shoot dry mass production when exposed to any of the herbicide treatments. The gas exchange responses of the bioindicator species following soil phytoremediation differed among treatments. Grain yield of S. bicolor was highest when L. multiflorum, the species mixture, and A. strigosa were used to remediate soils contaminated with diuron, sulfentrazone, and diuron + sulfentrazone, respectively. Likewise, H. annuus achieved the highest grain yield when F. esculentum, L. albus, and A. strigosa were used for the remediation of soils contaminated with diuron, sulfentrazone, and diuron + sulfentrazone, respectively. The use of green manures proved to be an effective strategy for reducing the persistence of diuron, sulfentrazone, and their combination in the soil. The bioindicator species exhibited superior performance when grown after the most efficient phytoremediating species, highlighting the importance of selecting appropriate cover crops to mitigate the residual effects of herbicides and promote greater sustainability in agricultural production systems.