Glyphosate loss by runoff and its relationship with phosphorus fertilization.

REPETTI, MARÍA ROSA; SASAL, MARÍA C.; DEMONTE, LUISINA; CISLAGHI, ANDREA; GABIOUD, EMMANUEL; OSZUST, JOSÉ; WILSON, MARCELO; BELDOMÉNICO, HORACIO R.

Santiago de Chile

Workshop; 5th Latin American Pesticide Residue Workshop; 2015

FiNet, Facultad de Agronomía e Ingeniería Forestal (Universidad Católica de Chile).

Agrochemicals more widely use in Argentina are nitrogen and phosphorus fertilizers and the herbicide glyphosate almost exclusively associated with the use of transgenic varieties of soybean. In Argentina, the Glyphosate (N-phosphonomethyl glycine) use is not only to control weeds pre and post implementation of a crop, but in the practice of chemical fallow for weed control, and the preservation of soil water content. The glyphosate in soil is adsorbed by phosphate linkages and degraded by microorganisms. This results in low mobility of both glyphosate and its main metabolite, amino methyl phosphonic acid (AMPA). The interaction between phosphorus and glyphosate in field conditions is unknown. The aim of this study was to evaluate the relationship between the application of glyphosate and phosphate fertilizer in their contribution to the contamination of surface water runoff. This study was conducted in an Acuic Argiudol soil (Tezanos Pinto series). Four treatments were raised on three date rainfall simulation of the application of fertilizer and herbicide with a completely randomized design delimiting 36 plots of 1 m2 each one. The soluble phosphorus in runoff water was determined by the colorimetric method of ascorbic acid. For the determination of glyphosate and AMPA a method based on the derivatization with FMOC, solid phase extraction (SPE) clean-up and UHPLC-MS/MS was employed. This study evidenced the competition between phosphorus-glyphosate for sharing sites of the Acuic Argiudol soil under no tillage. The phosphorus fertilizer application resulted in an increased loss of glyphosate by runoff after one day of application. These results suggests the need for further study to understand the interaction phosphorous-glyphosate in soil matrix and to determine appropriate times of applications with the goal of reduce risk of contamination by runoff.