Effects of the herbicide hexazinone on nutrient cycling in a low‐pH blueberry soil

Abstract

The herbicide hexazinone was applied as the commercial formulation Velpar L at field-rate (FR) concentrations of FR (14.77 microg ai g(-1)), FRx5 (73.85 microg ai g(-1)), FRx10 (147.70 microg ai g(-1)), FRx50 (738.50 microg ai g(-1)), and FRx100 (1477.00 microg ai g(-1)) to acidic soil, pH 4.12, taken from a lowbush blueberry field. Hexazinone was tested for inhibitory effects on various transformations of the nitrogen cycle and soil respiration. Nitrogen fixation was unaffected by hexazinone levels up to FRx100 following a 4-week incubation period. Ammonification was initially inhibited by all levels of hexazinone, but after 4 weeks, ammonification in all treatment systems was equal to or greater than the control. Nitrification was more sensitive to hexazinone; however, application at a field-rate level caused no inhibition. Inhibitory effects were noted above FR after a 2-month endpoint analysis and above FRx5 after a 6-month endpoint analysis. Hexazinone concentrations up to and including FRx100 stimulated denitrification. Soil respiration was also stimulated over a 3-week period when applied at a level up to 100 times the recommended field rate. In general, it was found that when applied at the recommended field application rate, hexazinone does not adversely affect the nitrogen cycle or soil respiration in acidic lowbush blueberry soils.

Functional and structural responses of soil N-cycling microbial communities to the herbicide mesotrione: a dose-effect microcosm approach

“…Dose-dependent response patterns observed in potential denitrification activity, with higher doses increasing stimulation, have been observed with other herbicides (Andersch and Anderson 1991;Pell et al 1998;Vienneau et al 2004). Overall, at higher doses than recommended field rates (10-100 μg a.i.…”

“…Similarly, other herbicides applied at doses far exceeding real field rate (upper several tens μg a.i. g −1 soil ) induced short-term decreases in nitrification (Andersch and Anderson 1991;Pell et al 1998;Vienneau et al 2004;Hernandez et al 2011). As evidenced by positive correlations between the PNA rates and the AOA or AOB abundances at day 6, a decrease in ammonia oxidizer abundances was likely responsible for PNA inhibition.…”

“…Most studies investigating the effects of herbicides (glyphosate, sulfonylurea, triazine) on the activities or structural endpoints of N-cycling microbial communities did not report significant impact of doses below 5 mg a.i. kg −1 soil (Carlisle and Trevors 1986;Stratton 1990;Andersch and Anderson 1991;Chang et al 2001;Vienneau et al 2004). Actually, our results for 10×FR (4.5 mg a.i.…”

Linuron effects on microbiological characteristics of sandy soils as determined in a pot study

“…Kara et al (2004) reported that the herbicide topogard significantly stimulated ammonification in neutral and alkaline soils, whereas acid soils showed significantly lower ammonium contents in comparison with controls. Ammonification was also initially inhibited by triazine herbicide hexazinone; however, ammonium contents were similar or greater in all treatments compared to controls after 4 weeks (Vienneau et al 2004). Studies on successive application of different pesticides in field conditions over 2 years, carried out by Schuster and Schröder (1990), showed that herbicides had only slight and transient sideeffects on the ammonification process.…”

“…Accinelli et al (2002) studied the short-term effect of six agrochemicals on microbial activity and reported that sulfonylurea herbicides applied up to 20 µg g −1 soil stimulated soil respiration, whereas application of these herbicides at the agricultural rate did not exert any significant impact on soil microbial activity. Soil respiration was also stimulated by hexazinone over a 3-week period, when it was applied at a level up to 100 times higher than the recommended field rate (Vienneau et al 2004). It would appear that some microorganisms are able to use applied herbicides as sources of energy and nutrients, resulting in an increase in their metabolic activity.…”