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Toxicological effects of herbicides on the non-target microorganisms in the soil that play important roles in degrading organic matter, nutrient cycling, and decomposition should be considered if they were applied at higher concentrations. This study was conducted to reveal the toxicity of three modern herbicides (dicamba + tritosulfuron; DT, isoxinutole + thlencarbuone-methyl + cyprosulfamide; ITC and nicosulfuron; N) on soil carbon mineralization for short term. Recommended concentration (25 g/day for DT1, 30 ml/day for ITC1, and 125 ml/day N1), its 5 (DT5, ITC5, and N5), and 10 (DT10, ITC10, and N10) folds of herbicides were applied on a clay soil with no pesticide application history. Soil + herbicide mixes and soil without herbicide as control were incubated under constant temperature (28 °C) and moisture (80% of soil field capacity) for 42 days. In general, all doses of herbicides were significantly decreased soil carbon mineralization in short term (P < 0.05). Cumulative carbon mineralization was declined for 3.4% by DT1, for 15.0% by DT5, for 22.4% by DT10, for 13.7% by ITC1, for 14.2% by ITC5, for 18.6% by ITC10, for 4.7% by N1, for 10.0% by N5, and for 21.0% by N10, respectively, compared to control. Significant decreases were observed in the rates of carbon mineralization except DT1 and N1. Results suggested that higher doses of these herbicides negatively affected on soil microbial respiration. [ABSTRACT FROM AUTHOR]

The large spatial heterogeneity in soil physico-chemical and microbial parameters challenges our ability to predict and model pesticide leaching from agricultural land. Microbial mineralization of pesticides is an important process with respect to pesticide leaching since mineralization is the major process for the complete degradation of pesticides without generation of metabolites. The aim of our study was to determine field-scale variation in the potential for mineralization of the herbicides glyphosate, bromoxyniloctanoate, diflufenican, and bentazone and to investigate whether this variation can be predicted by variations in basic soil parameters. Sixty-five soil samples were sampled from an agricultural, loamy field in Silstrup, Denmark, from a 60 × 165 m rectangular grid. The mineralization potential of the four pesticides was determined using a 96-well microplate C-radiorespirometric method. Initial mineralization rates were determined using first-order kinetics for glyphosate and bromoxyniloctanoate and zero-order kinetics for diflufenican and bentazone. The mineralization rates of the four pesticides varied between the different pesticides and the different soil samples, but we could not establish correlations between the pesticide mineralization rates and the measured soil parameters. Only the glyphosate mineralization rates showed slightly increasing mineralization potentials towards the northern area of the field, with increasing clay and decreasing OC contents. The mineralization potentials for glyphosate and bentazone were compared with 9-years leaching data from two horizontal wells 3.5 m below the field. The field-scale leaching patterns, however, could not be explained by the pesticide mineralization data. Instead, field-scale pesticide leaching may have been governed by soil structure and preferential flow events. [ABSTRACT FROM AUTHOR]

Glyphosate applied in association with atrazine provides the best cost/benefit for weed control for genetically modified corn. Therefore, the aim of this work was to evaluate the effects of applying glyphosate in mixture with atrazine on soil microbial population and on herbicides fate in a representative Oxisol from Brazil. The treatments consisted in applying the recommended field rate of glyphosate in association with 0, 1, and 2 times the recommended field rate of atrazine (and vice versa), plus the control (without herbicides application). The presence of atrazine temporarily (21 days) decreased soil microbial biomass (SMB) and increased soil carbon mineralization (SC, up to 13 times) and microbial metabolic quotient (qCO) due to the stresses caused by its toxicity. When the mixture was applied independent of the rates, SMB was recovered and the amounts of extractable and non-extractable C-residues were the same for both herbicides at 63 days. These results suggest that glyphosate may mitigate atrazine's temporary impact on soil microbes by supplying them nutrients during their adaptation. [ABSTRACT FROM AUTHOR]

Aim of this work was the development of a new non-biological factor to determine microbial in situ bioavailability of chemicals in soils. Pesticide residues were extracted from ten highly different agricultural soils that had been incubated with the 14C-herbicide isoproturon (IPU) under comparable soil conditions (water tension – 15kPa; soil density 1.3gcm−3). Two different pesticide extraction approaches were compared: (i) 14C-pesticide residues were measured in the pore water (PW) which was extracted from soil by centrifugation; (ii) 14C-pesticide residues were extracted from soil samples with an excess of water (EEW). We introduce the pesticide’s in situ mass distribution quotient (iMDQ) as a measure for pesticide bioavailability, which is calculated as a quotient of adsorbed and dissolved chemical amounts for both approaches (iMDQPW, iMDQEEW). Pesticide mineralization in soils served as a reference for real microbial availability. A highly significant correlation between iMDQPW and mineralization showed that PW extraction is adequate to assess IPU bioavailability. In contrast, no correlation exists between IPU mineralization and its extractability from soil with EEW. Therefore, it can be concluded that soil equilibration at comparable conditions and subsequent PW extraction is vital for a isoproturon bioavailability ranking of soils. [Copyright &y& Elsevier]