Leachability of glyphosate herbicide

Abstract

The main objective of this study was to investigate the leaching behavior of glyphosate and its metabolite aminomethyphosphonic acid (AMPA) with and without the influence of the chemical fertilizer N-P-K [in the ratio of 16:16:16] under rainy season and summer conditions. The specific effects of the chemical fertilizer on the accumulation of glyphosate and its metabolite aminomethyphosphonic acid in soil were determined. The experiment was performed under outdoor conditions by using soil columns. The leaching of glyphosate was monitored for 60 days, after that the residual glyphosate in the soil was evaluated. The amounts of glyphosate leaching influenced by the chemical fertilizer were clearly higher than the leaching that occurred without the influence of the chemical fertilizer. The total amounts of glyphosate leaching influenced by the chemical fertilizer were 6.53 % and 1.92% for rainy season and summer, respectively, while the total amount of glyphosate leaching in the soil columns that were not influenced by the chemical fertilizer was 0.03 % during both the rainy season and summer. The total AMPA leaching from the experimental groups were 2.77% and 1.82 % in the rainy season and summer, while the total AMPA in the rainy control group was 0.09%, the lowest result. In soil, the total accumulation levels of glyphosate influenced by the chemical fertilizer were 6.30 % and 2.39 % for the rainy season and summer, respectively, while the total accumulation of glyphosate when not influenced by the chemical fertilizer was 0.43%. For AMPA, the total accumulation levels of AMPA influenced by the chemical fertilizer were 7.35 % and 7.30 % for rainy season and summer, respectively, while the total accumulation of AMPA when not influenced by the chemical fertilizer was 1.77 %. From the results, the chemical fertilizer was seen to affect the behavior of both glyphosate leaching and accumulation in soil. The phosphorus contained in the chemical fertilizer replaced glyphosate in specific sorption sites by the competition mechanism. The replaced glyphosate then had the opportunity to form complexes with Ca and Mg. Consequently, its complexation was more difficult for the soil microbial organisms to degrade. The amounts of AMPA both in the leachate and soil were found to be related to the amount of glyphosate that remained after undergoing degradation.