W8 AM Agrochemicals and Pesticides
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in 337-338

(EDG-1117-731686) Sorption/desorption of 14C-Glyphosate on Plant Residues and Soil.

Edgar Ariel, Rampoldi¹, Susana, Hang¹, Enrique, Barriuso², ¹ Facultad de Cs Agropecuarias Universidad Nacional de Córdoba, Argentina, Argentina² UMR INRA-INA PG EGC Versailles-Grignon, Francia, Francia

ABSTRACT- In non-tillage systems the mulch developed is the first barrier before glyphosate (N-phosphonomethylglycine) reaches the soil. There is little information in relation to the magnitude and stability of the glyphosate-plant residues (PR) interactions. 14C-glyphosate sorption/desorption was studied on soybean and maize PR, on soil and on plant residue-enriched soil (to simulate the soil organic matter stratification) by means of batch equilibration method. Four different agroclimatic and pedologic regions of Córdoba, Argentina were selected. The glyphosate retention process on PR was limited (5 to 14% of 14C-glyphosate initially applied) and reversible. The Kfads values for maize-PR were higher than that of the soybean-PR, but the high parameter value dispersion suggest that is needed to consider the intrinsic variability of each PR. On soils, the percentage of 14C-glyphosate sorbed ranged from 72 to 93 % of it initial applied. Soils under soybean-maize (SM) rotation had higher glyphosate sorption and hysteresis, than soils with continuous soybean (SS). In relation to the geographic region, it was detected that sorption parameters decreasing from SE to NW direction and this is related to the granulometry of the soils, (sand content increase to NW); to the climate, (precipitation decrease SE to NW), and to increasing altitude towards NW. On soil+PR glyphosate behavior followed a pattern similar to that observed for soils though small variations due to PR origin were observed. It is possible in the long time crop situation these differences are expanded. The lowest glyphosate retention capacity and higher reversibility of the process on soils with continuous soybean suggests that the soil properties affected by soybean monoculture could be related to the capacity of the soil to retention glyphosate.

Key words: Glyphosate, No-tillage systems, Sorption/desorption, Plant residues