Persistence and Degradation of Pyrazon in Soil

Publisher Website
Google Scholar
Abstract
Based on bioassays of soil samples from field plots, the rate of disappearance of 5-amino-4-chloro-2-phenyl-3 (2H)-pyridazinone (pyrazon) was estimated with a multiple regression equation. Within a limited geographic region, pyrazon residues were directly related to the organic matter content of soil and inversely related to rainfall during the growing season. The bacteria population increased with the presence of pyrazon in soil at soil temperatures ranging from 4.5 to 29.5 C, indicating a wide capability of microbiological utilization of the herbicide in soil. There was no evidence that soil bacteria or actinomycetes were adversely affected by pyrazon. Thin layer chromatography of ethanol extracts of soil containing 3H-phenyl-labeled and 14C-pyridazinone-labeled pyrazon revealed that pyrazon is dephenylated to 5-amino-4-chloro-3-pyridazinone. In a sandy loam soil, less than 10% of the herbicide was degraded to 5-amino-4-chloro-3-pyridazinone after 10 weeks at 21 C.