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Evaluation of the effects of a diflufenican-containing combination herbicide on microbial activities in soil
Summary
The complete article is written in German
Under laboratory conditions two standard soils with or without lucerne meal, which were qualified for microbiological-ecotoxicological studies, were treated within several subtrials with the herbicide 'Fenikan' (diflufenican + isorpoturon), the test compounds 'RPA 41670 H' (diflufenican) and 'Arelon flüssig' (isoproturon) as well as with the reference compound 'Herbogil liquide D' (dinoterb). The amounts mixed into the soils resulted from the concentrations reached by simulated penetration of the area-related dosages into upper soil layers, where 5 cm depth represents the single dosage. To allow dose-effect relationships dosages up to 100 fold were used. As compared to the biocidal reference compound the single and 10-fold dosages of the test compounds produced only weak effects on the biomass-related dehydrogenase activity (DHA), on the substrate-induced short-term respiration (KZA) and on the carbon mineralization (LZA). Net N mineralization, however, was dose-related increased by 'Fenikan'. By using dose-effect relations an inhibition of the DHA occurred with 'Fenikan', but to a lesser extent with 'RPA 41670 H'. When looking to the respiration curve of the KZA during 48 hrs incubation some herbicide effects became visible which were not detectable within the 'normal' 6 hrs CO2 measurement. By comparing microbial activities in soil with and without lucerne meal (= LIA evaluation) which allowed the elimination of additional effects of introduced nutrients by the compounds, for the DHA some dose-related inhibitions occurred with the herbicide 'Fenikan' as well as with 'Arelon flüssig'. Furthermore the relationship of carbon and nitrogen mineralization showed a shift towards nitrogen by 'Fenikan' and sometimes by 'RPA 41670 H'. It seams that several factors (e.g. soil) can hamper identification of dose-related effects, especially when the test system is limited. Overall 'Fenikan' as well as the herbicides with only one of its active ingredients exerted relatively weak effects, although some clearly detectable influences occurred. Obviously the active ingredient isoproturon is mainly involved in these effects.
Relevance of glyphosate transfer to non-target plants via the rhizosphere
Summary
There is a common understanding that the widely used herbicide glyphosate is easily degraded and adsorbed in soils and thus, harmless for use in agriculture. We can demonstrate, however, that this conclusion is wrong and dangerous for farmers because in former risk assessments the behaviour of glyphosate in the rhizosphere was not properly considered.
In nutrient solution, rhizobox and pot experiments we can show that foliar applied glyphosate to target plants is released into the rhizosphere after a fast translocation from shoots to roots. In the rhizosphere glyphosate can obviously be stabilized long enough to achieve negative effects on non-target plants. Such a negative side-effect is for example inhibited acquisition of micronutrients such as Mn, but also Zn, Fe and B, which are involved in plant own disease resistance mechanisms.
From this glyphosate transfer from target to non-target plants (e.g. from weed to trees in orchards) we predict an increase in disease problems, particularly on soils with low micronutrient availability as already reported in the USA. In view of plant and soil health, we urgently call for a re-assessment of glyphosate as herbicide.
Effect of adjuvants on herbicide residues level in soil and plant
Summary
The aim of investigations was to understand the effect of herbicides and adjuvant application on residues in soil and sugar beet.
Field experiments were carried out from 2002 until 2004 on arable fields near Wroclaw (South-West Poland). Phenmedipham, desmedipham and ethofumesate were applied to control weeds in sugar beet at recommended and reduced doses alone and at reduced dose in mixture with three different adjuvants.
Samples of soil and roots of sugar beet were taken at day of harvest. Herbicide residues in all samples were analysed using high performance liquid chromatography with UV-detection.
The highest concentration of active ingredients were determined from plots, in which herbicides were applied in the full (recommended) dose. Reduction of herbicide dose caused a decrease of residues. The addition of adjuvants caused an increase of the residues of active ingredients in the soil and roots of sugar beet compared to plots with a reduced dose of herbicide without adjuvants. Residues of active ingredient of herbicides determined in roots of sugar beet did not exceed acceptable values for the EU.
Effect of Azoprim 50 WP and Isoturon 500 SC on the adenylate energetic charge of soil and the composition of soil microflora
Summary
The complete article is written in German
In a laboratory experiment isoproturon (Isoturon 500 SC) and atrazine (Azoprim 50 WP) degradation in soil and the influence on soil microflora was examined. During the incubation, counts of bacteria, actinomycetes and fungi were made, and percentage contribution of proteolytic, amylolytic and lipolytic bacteria on soil microflora was determined. In the same time the amount of ATP, ADP and AMP was analysed and the adenylate energy charge (AEC) calculated.
After 56 days, 70-85 % of isoproturon and about 40 % of atrazine was degraded. The investigation showed significant changes in different microbiological and biochemical parameters of the soil during degradation of both herbicides. The amount of ATP, ADP and AMP in herbicide treated soil changed, especially at the beginning of the experiment. For ATP a decrease was observed, while levels of ADP and especially AMP increased. Later on the amount of ATP slowly increased again and the other two adenylates decreased slowly during the rest of incubation. After the treatment of soil with herbicides a significant decrease of the adenylate energy charge was observed, which was proportional to the dose used. Later the AEC increased slowly, and at the end of the incubation time it reached about 0.8. Counts of all microorganisms in soil during herbicide degradation increased, especially that of bacteria and actinomycetes. For isoproturon this effect was apparent earlier, but it also disappeared earlier. Percentage of proteolytic, amylolytic and lipolytic bacteria on soil microflora increased during herbicide degradation. This tendency was more pronounced for isoproturon as for atrazine.
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