Herbicide behaviour in a boreal forest podzol

• Main Author: Helbert, Sheldon
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1986
• Subjects: Newfoundland
• Online Access: https://research.library.mun.ca/5518/; https://research.library.mun.ca/5518/1/Helbert_Sheldon.pdf; https://research.library.mun.ca/5518/3/Helbert_Sheldon.pdf

Keywords: Herbicide; Distribution; Persistence; Leaching; Forest; Podzol; Soil; 2,4-D; Dicamba; Hexazinone; Tebuthiuron; Picloram. -- There is inadequate information concerning herbicide persistence in soils of the boreal forest. A field study of herbicide behaviour in an Orthic Humo-Ferric Podzol began in the spring of 1983 in northeast central Newfoundland on a south-facing slope near Gambo Pond. 2,4-D, dicamba, hexazinone, tebuthiuron and picloran were applied on 5 test plots within a clear-cut site. Under stringent controls the LF, Ae, Bf, BC and C soil horizons were sampled up to 486 days after application. Residue analyses of samples from the soil horizons show the distribution of herbicides through the profile over time, and indicate each herbicide's propensity to leach and persist. Results show that all herbicides leach to all depths sampled indicating that there is the potential for contamination of lower levels including groundwater. The amounts detected in the lowermost horizon range from 0.9 mg a.i. per m² for picloram to 74.5 mg a.i. per m² for hexazinone (mg active ingredient values are adjusted for recovery, soil moisture, bulk density and horizon thickness). Initial application rates, varied between herbicides and are reflected in the residue concentrations detected. With the exception of tebuthiuron, 90 % of the herbicides disappeared from the soil 5 months after application. With the exception of picloram the herbicides persisted within the range of time intervals suggested by other authorities. Each ecosystem has particular sensitivities which must be buffered by environmental parameters (e.g., bulk density, clay and organic matter content, soil moisture and ambient temperature) limiting the movement and distribution of herbicides in the soil. Thus, herbicide use must be carefully managed to safeguard the natural environment.