Influence of more than 20 years (1988-2010) of reduced tillage (RT) practices on water and pesticide balances and dynamics is analyzed and compared to results from a conventional tillage plot (CT). The field study soils are described as silty clay stagnic luvisol, developed on a low permeable schist layer. A drainage network was set up according to French criteria (0.9 m deep, 10 m space) to avoid soil winter waterlogging. Climate is temperate oceanic and drainage generally occurs from November to March. Data were analyzed at yearly, weekly (pesticides) and hourly (water) time steps. Over the long term, cumulated drainage decreases significantly on RT (3999 mm) compared to CT (5100 mm). This differentiation becomes significant from 1999, 10 years after plowing was stopped. Strikingly, hourly drainage peak flows are higher under RT, especially during the second period (2000-2010), associated with low or no base flow. These results suggest a strong influence of the macropore network under RT practice. In particular, drainage peaks are higher at the beginning of the drainage season (mid-October to December). Consistently, pesticides applied in late autumn, which are the most quantified on this site, are often significantly more exported under RT. For atrazine, applied in spring, fluxes are linked to cumulative flow and are de facto higher under CT. For others pesticides, losses appear to be heterogeneous, with generally low or null export rates for spring application. Generally speaking, higher concentrations are measured on RT plot and explain observed exportation rate differences. Finally, there is no clear evidence of correlation between pesticide losses and long-term impacts of RT on hydrodynamics, pointing the importance of studying the short-term effect of tillage on water and especially solute flow.

The identification of intensive drainage periods is important for determining mitigation strategies for protecting water against pollution with plant protection products (PPPs). Most attempts to estimate the start, duration and the end of a drainage period are based either on mechanistic modelling approaches or on empirical knowledge about tile drainage. Mechanistic modelling requires many parameters, while the empirical approach does not allow for making the simulations and predictions needed for proposing reliable mitigation measures. In order to complement these two approaches, we have used a data-mining approach on data from 25 (1987-2011) agricultural seasons (campaigns) from the experimental station La Jaillière, France. The models for estimating the start and the end of the intensive drainage period for a particular campaign have the form of decision trees and tell us which factors influence these dates the most. The start of a drainage period depends mostly on the cumulative drainage and the cumulative rainfall since the beginning of the campaign and the average air temperature of the last 7 days. For estimating the end of a drainage period, the most important variables are the cumulative rainfall of the last 7 days and the average air temperature of the following 7 days. Copyright © 2015 John Wiley & Sons, Ltd.key words: tile drainage; drainage period; empirical data; data mining; decision trees Received 13 January 2014; Revised 16 January 2015; Accepted 16 January 2015 RÉSUMÉ L'identification des périodes d'écoulement, et plus particulièrement la saison de drainage intense, est importante pour mettre en oeuvre des stratégies de limitation du risque de transfert des produits phytosanitaires dans les eaux. La plupart des démarches appliquées pour estimer le début, la durée et la fin de la période de drainage sont basées sur des modèles mécanistes ou sur la connaissance empirique du fonctionnement des réseaux de drainage. Les modèles mécanistes requièrent généralement de nombreux paramètres, et l'approche empirique ne permet pas de faire des simulations et des prédictions, indispensables pour la mise en place de mesures efficaces d'atténuation du risque. Dans le but de compléter ces deux approches, nous avons utilisé une méthodologie basée sur la fouille de données (data mining), en valorisant les informations recueillies durant 25 campagnes (1987 à 2011) par ARVALIS Institut du végétal sur le dispositif expérimental de La Jaillière à la Chapelle-Saint-Sauveur (Ouest de la France). Les modèles développés pour simuler les dates de début et fin de drainage prennent la forme d'arbres de décision qui hiérarchisent les facteurs ayant le plus d'influence sur la détermination de ces dates. Ainsi, la date de début du drainage dépend principalement de la quantité de pluies cumulées depuis le début de la campagne (1er septembre), mais aussi du cumul d'eau drainée, ainsi que de la température moyenne durant les sept jours précédents. La simulation de la date

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This study was carried out within the framework of a multidisciplinary project for evaluating buffer zones for combating pesticide contamination of surface water. Such areas are effective in removing pesticides transported by run-off; however, little information is available about the fate of the pesticides so intercepted. Two herbicides having contrasting properties (isoproturon, moderately hydrophobic (log Kow = 2.5), diflufenican, strongly hydrophobic (log Kow = 4.9)) and isopropylaniline (an isoproturon metabolite) were used for characterising sorption and desorption from soil having three different land uses: grass buffer strip, woodland and cultivated plot. The experiments were carried out in controlled laboratory conditions using isoproturon labelled with 14C in the benzene ring. The results demonstrated that diflufenican and isopropilaniline retention was more significant than isoproturon in three soils. The three molecules’ Kd values revealed that isoproturon and diflufenicanil retention was more important in woodland soil where carbon content was more significant (ZB 0-2: Kd IPU = 15.1 Ls kg-1; Kd DFF = 169.2 Ls kg-1). Isopropilanilina Kd was higher in grass buffer strip soil (BE 0-2: Kd IPA = 53.1 L kg-1). These differences were related to different organic matter content and nature according to the type of land use.

BACKGROUND Thanks to the changes in aquatic risk assessment within the marketing authorization (MA) process in France, the contamination of surface water through the subsurface drainage network is better accounted for. The measure adopted by risk regulations is to prohibit any use of selected pesticides on drained plots. Herbicide solutions on subsurface‐drained plots are becoming scarce due to a limited number of innovations combined with the re‐approvals process. Autumn weed management then becomes a major issue for winter cropping systems on drained plots. Unlike runoff prevention, few risk management measures are available to prevent the risks associated with drained plots. RESULTS We analyzed data from La Jaillière, an ARVALIS experimental site (nine plots, 1993 to 2017), representative of scenario D5 from the EU FOCUS Group, for four herbicides (isoproturon, aclonifen, diflufenican, flufenacet). Our study demonstrates the relevance of the time application management measure by showing the decreasing trend in the transfer of pesticides in drained plots. In addition, it validates, still on the La Jaillière site, the hypothesis of a management measure based on an indicator of soil profile saturation before drainage flow (soil wetness index, SWI). CONCLUSIONS A conservative measure consisting of restricting pesticide applications during autumn, when the SWI is <85% of saturation, reduces the risk by a factor of 4–12 for quantification above the predicted no‐effect concentration and values of maximum or flow weight average concentrations by 70‐ and 27‐fold, ratio of exported pesticide by 20‐fold, and total flux by 32. This measure based on SWI threshold appears to be more efficient than those using other restriction factors. SWI can be easily calculated by considering the local weather data and soil properties for any drained field. © 2023 Society of Chemical Industry.

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