RESUMO
Glyphosate is one of the most widely used herbicides, but is still in the spotlight due to its controversial impact on the environment and human health. The main purpose of this study was to explore the effects of different glyphosate usages on harvested grain/seed contamination. Two field experiments of different glyphosate usage were carried out in Central Lithuania during 2015-2021. The first experiment was a pre-harvest application, with two timings, the first according to the label (14-10 days), and the other applied 4-2 days before harvest (off-label), performed in winter wheat and spring barley in 2015 and 2016. The second experiment consisted of glyphosate applications at label rate (1.44 kg ha-1) and double dose rate (2.88 kg ha-1) at two application timings (pre-emergence of crop and at pre-harvest), conducted in spring wheat and spring oilseed rape in 2019-2021. The results suggest that pre-emergence application at both dose rates did not affect the harvested spring wheat grain or spring oilseed rape seeds-no residues were found. The use of glyphosate at pre-harvest, despite the dosage and application timing, led to glyphosate's, as well as its metabolite, aminomethosphonic acid's, occurrence in grain/seeds, but the amounts did not reach the maximum residue levels according to Regulation (EC) No. 293/2013. The grain storage test showed that glyphosate residues remain in grain/seeds at steady concentrations for longer than one year. A one year study of glyphosate distribution within main and secondary products showed that glyphosate residues were mainly concentrated in wheat bran and oilseed rape meal, while no residues found in cold-pressed oil and wheat white flour, when glyphosate used at pre-harvest at the label rate.
RESUMO
The establishment of the harmful pathogen Fusarium graminearum in different agroecosystems may strongly depend on the ability of the soils to suppress its development and survival. This study aimed to evaluate the influence of different soil tillage systems (i.e., conventional tillage, reduced tillage and no-tillage) on soil fungistasis against F. graminearum. Soil samples were collected three times during the plant growing season in 2016 and 2017 from a long-term, 20-year soil tillage experiment. The F. graminearum in the soil samples was quantified by real-time qPCR. The soil fungistasis was evaluated by the reduction in the radial growth of F. graminearum in an in vitro assay. The antagonistic activity of the soil bacteria was tested using the dual culture method. The F. graminearum DNA contents in the soils were negatively correlated with soil fungistasis (r = -0.649 *). F. graminearum growth on the unfumigated soil was reduced by 70-87% compared to the chloroform fumigated soil. After the plant vegetation renewal, the soil fungistasis intensity was higher in the conventionally tilled fields than in the no-tillage. However, no significant differences were obtained among the tillage treatments at the mid-plant growth stage and after harvesting. 23 out of 104 bacteria isolated from the soil had a moderate effect, and only 1 had a strong inhibitory effect on the growth of F. graminearum. This bacterium was assigned 100% similarity to the Bacillus amyloliquefaciens Hy7 strain (gene bank no: JN382250) according to the sequence of the 16S ribosome subunit coding gene. The results of our study suggest that the presence of F. graminearum in soil is suppressed by soil fungistasis; however, the role of tillage is influenced by other factors, such as soil biological activity, type and quantity of plant residues and environmental conditions.
