Extrato pirolenhoso: controle de plantas daninhas, seletividade para espécie cultivada e impacto sobre a macrofauna do solo

Abstract

Wood vinegar, a byproduct of wood pyrolysis, has attracted interest in agriculture due to its wide range of functions, such as insecticide, fertilizer, soil disinfectant, and, more recently, its potential as an herbicide, among other agricultural applications. This study aimed to evaluate the effects of different fractions (raw, decanted, and distilled) and concentrations of pyroligneous extract on the control of capim-annoni (Eragrostis plana Ness) and Euphorbia heterophylla (wild poinsettia), its selectivity for common bean (Phaseolus vulgaris) cultivation, and its effects on earthworm behavior (Eisenia fetida). Pre- and post-emergence trials were conducted for the weed species and for common bean using the three extract fractions mentioned, at concentrations of 0, 10, 25, 40, 55, 70, 85, and 100%. In addition, avoidance tests with Eisenia fetida earthworms were conducted in two soil types (artificial and natural), testing the raw, decanted, and distilled fractions at concentrations of 0, 8, 20, 32, 44, and 68%. Eragrostis plana and Euphorbia heterophylla showed significant reductions in mean emergence time, emergence speed index, height, fresh mass, and root length—especially with higher concentrations of pyroligneous extract applied in pre-emergence. In post-emergence, phytotoxicity was intense and progressive, being more pronounced with the decanted extract. Considerable mortality rates were observed at concentrations above 55%, particularly in Euphorbia heterophylla. In the common bean trials, higher concentrations in pre-emergence delayed germination and reduced root growth and fresh root mass, although no visible phytotoxicity symptoms were observed. In post-emergence, the decanted extract was the most phytotoxic, followed by the raw and distilled extracts, with the distilled extract being the most selective to the crop. In artificial soil, all fractions of the extract showed significant toxicity to earthworms, regardless of concentration, with escape rates exceeding 80%. In contrast, in natural soil, the extract was not considered toxic, with avoidance rates below 30% at some concentrations—and 0% in most cases—indicating that the physicochemical characteristics of the soil directly influence the bioavailability of the extract's compounds. The results indicate that pyroligneous extract has potential for use as an alternative in weed management, with variable selectivity depending on the fraction and concentration applied. However, the toxicity observed in artificial soil raises concerns and underscores the need for careful environmental assessment, considering soil type and potential impacts on soil organisms.