Biodisponibilidade e efeito de herbicidas pré-emergentes na microbiologia em solos do Cerrado

Abstract

Herbicides are applied and reach the soil, Herbicides undergo processes of sorption, transport, and transformation when applied and reach the soil, as well as their activity are affected and impact the environment. In this context, the aim of this study was to evaluate the bioavailability and microbiological impacts of diclosulam, imazethapyr + flumioxazin, pyroxasulfone + flumioxazin, S-metolachlor, and trifluralin in three Cerrado soils. Five experiments were conducted separately for each herbicide or combination in a greenhouse, using a completely randomized design in a 3 × 8 factorial scheme with five replicates. The factors included three soil types (LVAd – Rhodic Haplustox, RQo – Typic Quartzpsamment, LVd – Rhodic Haplustox) and eight herbicide doses (0, 1/16x, 1/8x, 1/4x, 1/2x, x, 2x, 4x) tested on Eleusine indica and Conyza bonariensis. Phytotoxicity (%F), plant dry matter and weed control percentage (%C) were determined at 35 days after application (DAA). To further evaluate the effects on soil microbiology at 35 DAA for the doses 0, x, and 2x, microbial biomass carbon (C-BMS), basal microbial respiration (RBS), and metabolic quotient (qCO2) were determined. Phytotoxicity (%F) was influenced by the interaction between herbicide and soil for all molecules. For diclosulam, imazethapyr + flumioxazin, pyroxasulfone + flumioxazin, and S-metolachlor, the soils exhibited similar responses, with symptom severity increasing with higher doses. The lowest %F values were observed for trifluralin, which nonetheless exceeded 80%. Results showed that weed control percentage (%C) was influenced by the herbicide-soil interaction for diclosulam, imazethapyr + flumioxazin, S-metolachlor, and trifluralin, while pyroxasulfone + flumioxazin was affected only by the herbicide. Trifluralin was ineffective in controlling Eleusine indica. Diclosulam, imazethapyr + flumioxazin, pyroxasulfone + flumioxazin, and S-metolachlor demonstrated potential for dose adjustment in the control of Conyza bonariensis and Eleusine indica, with the optimal dose varying according to soil type. In soil microbiology, diclosulam influenced C-BMS. RBS and qCO2 were affected by soil type, with RQo showing the lowest RBS and highest qCO2 values. The imazethapyr + flumioxazin mixture affected qCO2, with higher values observed at lower doses in RQo. Soil type increaswed C-BMS and RBS, with the highest C-BMS values recorded­ in LVAd and LVd soils, while the lowest RBS was observed in RQo. Pyroxasulfone + flumioxazin and S-metolachlor did not significantly affect the evaluated parameters. It was concluded that herbicide effects varied depending on the molecule and soil type.