The Sousson drainage basin in the Gers dpt of France

摘要

A study of the relationship between weed control of maize crops and water quality was conducted since 1998 in the Sousson drainage basin, in Southwest France. Measurements of the levels of plant protection product residues in water leaving the ploton three different sites made it possible to compare the effects of a range of weed control programmes and/or plot layout: with or without grassed strips at the lower end of the plot, with or without atrazine, single or mixed weed control (i.e. chemicalcontrol coupled with machine-assisted control). The study produced the following results: (i) transfer to water of a small fraction of herbicides (less than 2% of inputs), mainly during the first run-off of water following application; (ii) concentrations of residues are higher as the time-lapse between application and rainfall leading to run-off is shorter; (iii) grassed strips play a purifying role, leading to a clear reduction in the amount of residues transferring into water; and (iv) difficulties for mixed weed control linked to local conditions (soil, climate and flora). Finally, measurements taken at the mouth of the drainage basin produced comparable results to those taken on water leaving the plot.