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

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.