The influence of hexazinone on carbon dioxide evolution and mineralization of nitrogen, phosphorus and sulfur in a forest soil

The effect of hexazinone (applied as Velpar L.) on carbon dioxide (CO2) evolution, nitrogen (N), phosphorus (P), and sulfur (S) mineralization in a surface organic layer (L–H horizons) of a forest soil was followed during a 150-d laboratory incubation. Hexazinone was applied at recommended field rates equivalent to 2 and 4 kg a.i. ha−1 and at a higher rate, 8 kg a.i. ha−1. A bioassay determined that hexazinone at 4 and 8 kg a.i. ha−1 affected the root and shoot biomass of oats for up to 63 d after application. Hexazinone had no effect on CO2 evolution, ammonification, nitrification or net S mineralization in the L–H horizons. An increase in extractable P was found in the hexazinone-treated soils at the end of the incubation. Hexazinone applied at recommended field rates of 2 and 4 kg a.i. ha−1 would have little direct impact on nutrient-cycling processes in the L–H horizons of mixed-wood cutovers.