Search

Finely divided carbon char products offer a cost-effective method for the safening of herbicides in soil. In this investigation, two contrasting carbon char sources: Virgin Activated Charcoal (VAC) and Recovered Carbon Black (RCB) products were evaluated for safening of metsulfuron, sulfentrazone and pyroxasulfone herbicides in soil using sugar beet bioassay, and of rimsulfuron using perennial ryegrass bioassay. Plants were grown for seven days in WhirlPack® bags in soil with added carbon char product and added herbicide, and the root or shoot lengths were measured. The VAC was more efficacious in herbicide safening than the RCB. For the VAC, concentrations in soil (wt/wt) as low as 0.375% fully deactivated metsulfuron, sulfentrazone and pyroxasulfone, while for the RCB product a gradual degree of safening was observed, except for pyroxasulfone that was completely deactivated by both VAC and RCB. The VAC at concentrations of 3% and above fully deactivated rimsulfuron, while RCB did not. The two carbon char products examined in this study had different physical properties, of which the specific surface area (91 and 515 m2 g−1 for the RCB and VAC, respectively) and specific surface area of pores (75 and 247 m2 g−1 for RCB and VAC, respectively) showed the greatest difference. Higher surface area promoting greater sorption may explain more effective deactivation of herbicides by the VAC. To obtain the same degree of herbicide safening, more RCB would be required. [ABSTRACT FROM AUTHOR]

The relationship between pyroxasulfone bioactivity and soil properties has not been investigated in a wide range of soils typical of western Canada. In this study, 47 soils from Saskatchewan, Manitoba and Alberta, with varying organic matter content (1.5%–22.1%), pH (5.0–7.9), and clay content (6.8%–59.4%) were used to evaluate the effect of soil properties on pyroxasulfone bioactivity and its relevance to field application rates. Bioactivity was assessed by measuring the reduction of sugar beet shoot length after 7 days in response to 0, 92, 184, and 368 µg ai kg−1pyroxasulfone concentration in soil. Multiple regression analysis showed that pyroxasulfone bioactivity was related to soil organic matter content, pH and clay content. Grouping the soils according to these properties allowed for a summarization of pyroxasulfone field application rates required to achieve bioactivity based on the magnitude of sugar beet shoot length inhibition (%). The estimated field application rates ranged from less than 120–480 g ai ha−1. [ABSTRACT FROM AUTHOR]