Search Results (3)

This study evaluates the pseudo-persistence of glyphosate over three growing seasons in agricultural soils (gleysol) in Québec, Canada. The experiment was carried out in long established plots following a corn–soybean–wheat rotation cycle with various combinations of N-fertilization (mineral N-fertilization, organic N-fertilization, without fertilization) and tillage techniques (conventional tillage and no-till). The periods between glyphosate applications were 250, 326, and 398 days. Soil sampling was carried out at 0–20 cm and 20–40 cm just before each new application of herbicide. Glyphosate was not detected in any sample. Its main degradation product, aminomethylphosphonic acid (AMPA), was found and quantified in approximately 50% of the samples. The detection frequency of AMPA was higher for conventional tillage compared to no-till. Levels ranged between 0.09 and 0.46 μg.g⁻¹. The molar balance per hectare over the first 40 cm showed that the amount of glyphosate present in the form of AMPA in the soils sometimes exceeds the amount of glyphosate applied during the previous season (10.54 or 5.27 mol glyphosate.ha⁻¹). The cumulative effect of glyphosate applications on AMPA levels over the 3 years, however, has not been demonstrated. The effect of conventional tillage on the persistence of AMPA is significant in 2 out of 3 years. The persistence of AMPA was higher for combinations of conventional tillage/mineral N-fertilization and conventional tillage/without fertilization practices. We suggest that conventional tillage can modify parameters related to soil structure or to the structural or functional composition of the bacterial community, which could impact the degradation and leaching of glyphosate and AMPA. Full article

Glyphosate-based herbicide (GBH) usage is ubiquitous in Quebec field crops, apart from organic management. As glyphosate generally degrades rapidly in agricultural soils, aminomethylphosphonic acid (AMPA) is produced and persists longer than glyphosate. Repeated GBH applications year after year raise questions about glyphosate and AMPA pseudo-persistence in soils and its possible impacts on the soil microbial community. This research aims at understanding the influence of cropping systems and edaphic properties on glyphosate and AMPA contents and on the diversity and composition of the soil microbial community across nine field crop fields located in Southern Quebec (Canada) during 2019 and 2020. Average glyphosate soil contents (0.16 ± 0.15 µg·g⁻¹ dry soil) were lower than average AMPA soil contents (0.37 ± 0.24 µg·g⁻¹ dry soil). Glyphosate and AMPA contents were significantly lower at sites cultivated under organic management than conventional management. For conventional sites, cumulative GBH doses had a significant effect on glyphosate soil contents measured at the end of the growing season, but not on AMPA soil contents. Sites with higher GBH applications appear to accumulate glyphosate over time in the 0–40 cm soil horizon. Glyphosate and AMPA soil contents are inversely proportional to soil pH. Soil prokaryotic and fungal communities’ alpha-diversity, beta-diversity, and functional potential were not impacted by cumulative GBH doses, but rather by soil chemical properties, soil texture, crop rotation, and manure inputs. Full article

A large amount of glyphosate enters the soil at a high frequency, forming “pseudo-persistent” pollutants that, in turn, threaten soil ecological function and crop growth. Earthworm casts (EWCs) are a sound organic alternative to chemical fertilizers to promote crop growth. Dissolved organic matter from EWCs (EWC-DOM) is supposed to be a more mobile and bioavailable fraction. However, the effect of EWC-DOM on the phytotoxicity of glyphosate remains largely unknown. This study examines glyphosate-induced oxidative stress and its impact on antioxidant and detoxification enzymes in citrus plants grown in soils with and/or without EWC-DOM. The results suggest that EWC-DOM could reduce the membrane lipid peroxidation level, thus slowing down the aging of plants in order to maintain stronger resilience, with more active antioxidant enzymes (including SOD, POD, and CAT) and detoxification enzymes (including GST, laccase, CPR, and UGTs) that could effectively remove reactive oxygen species (ROS) caused by glyphosate stress, thereby alleviating the damage of ROS accumulation on plant tissues. Our data indicate that incorporating EWC-DOM should be a sound way to protect citrus plants from the phytotoxicity caused by using glyphosate for orchard weeding. This has major implications for the sustainable and healthy development of citrus production. Full article