Studies on the biodegradation capacity of 14C-labelled glyphosate in vine plantation soils

Glyphosate is among the most widely used broad spectrum herbicides in the world because they are highly efficacious, cost effective, practically non-toxic and degrade readily in the environment. The herbicide is inactivated and biodegraded by soil microbes, degradation rate depends on soil microbial activity and factors that affect this activity. Glyphosate degradation rates vary considerably across a wide variety of soil types and microflora population types. The aim of this paper was to study the biodegradation capacity of glyphosate in soil samples prelevated from vine plantation from Timis county, Romania, belonging to Banat's University of Agricultural Science, Timisoara, in presence of organic and inorganic supplement, at different concentration levels. After addition of glyphosate-phosphonomethyl-C-14-labeled, the accumulated (CO2)-C-14 (as % of total C-14) was monitored during 44 days. Investigated soil shows a high degradation capacity of over 85% of total radioactivity after 44 days from the treatment application. Addition of inorganic supplement causes a decrease of glyphosate biodegradation capacity to 10.77-12.87% of total radioactivity, while in presence of straw the accumulated (CO2)-C-14 (as % of total C-14) during the 44 days ranged between 59.97 and 87.58%. The amount of (CO2)-C-14 released reached the highest level in the first 4 days after herbicide application, both in control and experimental variants with organic and inorganic supplement (from 2.61 to 30.27% of total radioactivity). By glyphosate addition the growth and multiplication of soil microorganisms, whose biomass is digested in the range of 9-12 days of treatment, according to the daily mineralization rate (DMR) values, is stimulated. Our results on the activity of microorganisms showed that glyphosate degradation in soil is mainly performed by micromyces.