Sustainable grass cover management of vineyards enhances pesticide sorption

Vine is one of the most treated crops. In the Mediterranean area, vineyards are vulnerable to runoff and erosion, both vectors of pesticide dispersion. The substantial pesticide use along with acute dispersal risk threatens the surrounding water bodies. Pesticide sorption contributes to regulate their dispersal. Identifying sustainable management practices enhancing sorption is key to improve water quality. Vineyard cover cropping regulates runoff and erosion. Yet its influence on the sorption of contrasted pesticides and its variability remains to be characterized. Accordingly, this study evaluated the effects of grass cover management on the sorption of widely used pesticides. The study site was a catchment in Southern France, part of a long-term observatory, where grass cover has been monitored for the past 20 years. Topsoil was sampled from the vine rows and inter-rows of 23 vineyards. These vineyards had diverse soils, slopes, and grass cover rates. The adsorption coefficient of the soils was measured for two herbicides, glyphosate and napropamide, and a fungicide, difenoconazole. This study highlights the heterogeneity in cover cropping strategies. Spontaneous cover cropping dominated, and the most popular pattern was to alternate frequently tilled inter-rows and grassed inter-rows. For most of the vineyards, the rows and the tilled inter-rows had low-medium grass cover rate (0–50%). The majority of the grassed inter-rows had high grass cover rate (50–75%). The sorption coefficients of napropamide, difenoconazole, and glyphosate were similar for the vine rows and tilled inter-rows and significantly greater in grassed inter-rows. This was related to an increase of soil organic carbon from the low to high grass cover class. Other catchment characteristics did not affect pesticide sorption. This is the first study evaluating the influence of vineyard cover cropping on the sorption of pesticides at the catchment scale, and it shows that it is an efficient lever to enhance it.