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Contact: pare@supagro.inra.fr; International audience; Soil surface characteristics (SSC) influence strongly hydrological processes and are known to vary largely in space and time according to soil characteristics and soil management. Because tillage is a main source of variation, the goal of this study was to present and evaluate a prediction model of the temporal variation of the SSC after tillage at the catchment level. The study focused on bare soils prevailing in spring and summer. A logistic regression approach was used to predict the evolution along three stages, starting from the fresh tillage stage to the crusted soil stage. This method provides the probabilities of occurrence of each stage. The predictor candidates tested were a rainfall characteristic, namely cumulative rainfall depth or cumulative kinetic energy, basic soil properties and tillage features. The results showed that a model based on cumulative kinetic energy since tillage and soil stoniness accurately predicts the dynamics of SSC: the rate of well classified SSC was 91%. However, no significant difference in the prediction performance was found using as predictor either cumulative kinetic energy or cumulative rainfall amount since tillage. In the prediction model, the rainfall characteristic was the most significant predictor for the SSC evolution and the only one during the first stages of crust development since tillage. Stoniness was also shown to influence SSC evolution but only during the last stages of crust development: high stone cover speeds up soil surface evolution. The same approach using logistic regression can be applied elsewhere but will require a re-examination of the most relevant predicting variables. Finally, to be able to predict the soil surface characteristic evolution on an annual scale, weed growth characteristics must be considered in the list of predictor candidates.

Contact: silvio.gumiere@gmail.com; International audience; In this paper, we present MHYDAS-Erosion, a dynamic and distributed single-storm water erosion model developed as a module of the existing hydrological MHYDAS model. As with many catchment erosion models, MHYDAS-Erosion is able to simulate sediment transport, erosion and deposition by rill and interrill processes. Its originality stems from its capacity to integrate the impact of land management practices (LMP) as key elements controlling the sedimentological connectivity in agricultural catchments. To this end, the water-sediment pathways are first determined by a specific process-oriented procedure defined and controlled by the user, which makes the integration of LMP easier. The LMP dynamic behaviours are then integrated into the model as a time-dependent function of hydrological variables and LMP characteristics. The first version of the model was implemented for vegetative filters and tested using water and sediment discharge measurements at three nested scales of a densely instrumented catchment (Roujan, OMERE Observatory, southern France). The results of discharge and soil loss for simulated rainfall events have been found to acceptably compare with available data. The average R(2) values for water and sediment discharge are 0.82 and 0.83, respectively. The sensitivity of the model to changes in the proportion of LMP was assessed for a single rain event by considering three scenarios of the Roujan catchment management with vegetative filters: 0% (Scenario 1), 18% (Scenario 2, real case) and 100% (Scenario 3). Compared to Scenario 2 (real case), soil losses decreased for Scenario 3 by 65% on the agricultural plot scale, 62% on the sub-catchment scale and 45% at the outlet of the catchment and increased for Scenario 1 by 0% on the plot scale, 26% on the sub-catchment scale and 18% at the outlet of the catchment.

Correspondance: saison@supagro.inra.fr; International audience; The availability of pesticides in the soil is one of the factors that determine their mobilization and transport in runoff and groundwaters. In this paper, we aim to better understand the change in pesticide availability with increasing residence time in the soil. The relative contributions of degradation and sorption to the overall fate of molecules were examined, as was the remobilization of residues from the topsoil in water. The experiment was undertaken in undisturbed soil micro-lysimeters under natural climatic conditions for 1 year. We applied 14C-diuron to the soil surface to trace its residues in water-extractable (W), methanol-only-extractable (MO) and non-extractable (N) fractions and in runoff waters. Mass-balance calculations were fitted to the observed data to determine the quantities degraded or transferred within and between each of the compartments studied. Losses of diuron residues in runoff declined exponentially from 473 to 4 µg l−1 in 1 year. After 80 days, sorption of diuron residues in the soil was significant, as was degradation in the W and MO pools. Losses in runoff were small because of sparse rainfall. The following 140 days corresponded to a humid period with increased degradation in both W and MO pools. A redistribution from the MO towards the W pool occurred, probably because of intense rainfall at that time, leading to an apparent desorption of diuron residues. This was the most important result, suggesting that ageing processes should not be considered irreversible over time. The last phase of change, which occurred during winter, was slow. Leaching processes appeared to be of minor importance for diuron, with the surface layer containing more than 84% of diuron residues

Correspondance auteur: Raclot D. raclot@supagro.inra.fr; International audience; Soil erosion surveys and modeling approaches often rely on datasets collected from small experimental plots or fields. Therefore, one important issue is to assess to what extent reference data collected on small areas can be affected by soil tillage practices and extrapolated to larger areas. The objectives of this paper are to discuss: (i) the impact of superficial tillage on the erosion rates at field scale and (ii) the impact of the scale on the erosion rates for areas ranging from small fields to 1 km(2) catchments. We analyzed a dataset of 18 rainfall events including runoff and erosion data from fields of approximately 1200 m(2) and 3200 m(2) consisting of vineyards with two contrasting weeding practices - either superficial tillage or notillage with chemical weeding - and from the outlet of a 0.91 km(2) catchment that was 70% vineyard. Results showed that superficial tillage significantly reduced (4.5 times) soil losses as compared to notillage, with a large event-to-event variability. Considering the natural conditions studied by the authors, no-tillage with chemical weeding is not recommended for the study area. Erosion rates observed at catchment scale were significantly lower than those observed at the scale of individual fields. This trend, which has already been observed by many researchers, confirms that catchment soil loss cannot be estimated by the sum of individual field soil losses. In this context, the scaling transition between the field and the 1 km(2) catchment can be analyzed in terms of the spatial variability of soil management and connectivity between the sediment-producing and deposition areas

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Abstract: In tropical humid environments under intensive banana production, pesticide transfer in waters can be of particular concern due to heavy rainfall, steep slopes, and soils with high infiltration capacities. The transfer in percolation and runoff waters of the nematicide cadusafos was investigated during a three month field experiment. The spatial heterogeneity of the banana plantation was taken into account by measuring percolation fluxes both under the banana plants and in the interrows with a specially designed lysimeter device installed at 60 cm depth. At the field scale, 0.34% of the pesticide applied was transferred in percolation, 0.13% in runoff. Forty-nine percent of cadusafos losses occurred by percolation under the banana plants, 23% by interrow percolation, and 28% by runoff. Losses were highest during the three weeks following cadusafos application, and this is also when dissipation in the soil was highest (calculated half-life in the soil: 7d). After this period, losses of cadusafos were low, both in soil and waters. Under the banana plant, saturated fluxes carried most of the pesticide, despite total percolation fluxes being at least five-times higher than saturated ones. Although overall pesticide transfer in water was low (0.5% of applied), it was not negligible due to the frequency of pesticide application in these areas

E-mail addresses: louchart@supagro.inra.fr; International audience; Realistic estimation of sorption parameters is essential to predict long-term herbicide availability in soils and their contamination of surface water and groundwater. This study examined the temporal change of an effective partition coefficient K-d(eff) for the herbicides simazine, diuron, and oryzalin from a 0.12 ha field experiment during 7 vineyard growing seasons. K-d(eff) is the ratio of solvent extractable herbicide concentrations in the top soil (0-2 cm) to the average concentrations in runoff water and is considered to assess the effective availability of herbicides to runoff transfer. K-d(eff) increased largely with aging time since application, from values similar to those of the literature (determined in 24 h batch conditions, K-d(ref)), up to 88, 164, and 30 times these initial values for simazine, diuron, and oryzalin respectively. The seasonal variation of K-d(eff) values between years and compounds could be adequately described by a unique model, taking into account the cumulative rainfall since application and K-d(ref) of each compound. This simple model was able to represent the influence of the soil moisture content and its changes in the different biological and physicochemical processes that may contribute to the (bio)available, sorbed, or entrapped state of any of the studied herbicides with aging time under Mediterranean climate.

Corresponding author. fax: +49 381 498 2159. E-mail address: bernd.lennartz@uni-rostock.de (B. Lennartz).; International audience; This work was initiated to study the effects of climate induced soil water status variations which can reach extreme values under natural conditions on the sorption process of hydrophobic organic compounds. Based on the classical slurry batch methodology an approach is developed that allows the fast and careful complete drying of soil suspensions (microwave technique). Classical adsorption experiments were followed by three desorption steps with and without drying cycles. Drying and re-wetting enhanced the sorption-desorption hysteresis and Freundlich adsorption coefficients increased from 5.9 to 16 and 5.2 to 21 over three drying cycles for diuron and terbuthylazine respectively. Assuming the validity of a dual stage adsorption process, model evaluation suggests that drying is as a shrinking-like process leading to conformational changes of the dominant sorbent (soil organic matter) which restrict the intra-micro-particle diffusion. Rewetting only leads to a partial recovery of the diffusional pore space.

International audience; The assessment of field-like sorption behaviour is critical to predict the fate and transport of organic compounds, especially when long time periods are considered. We compared field-derived sorption isotherms for diuron from a 4-year database collected in a Mediterranean catchment with adsorption and desorption isotherms from classical batch studies. In addition, a new technique of drying the slurry samples in-between various desorption steps was applied in order to reflect the recurrent drying of the topsoil under Mediterranean climate conditions. Our results show first that the field-derived isotherms indicated a larger sorption capacity of the soil at small diuron concentrations (larger Kf and smaller exponent for the Freundlich parameters) than those derived from standard batch experiments. Second, when the soil was dried before desorption, chemical release was reduced by up to 29% as compared with normal desorption, resulting in isotherms that were in line with results from the field experiment. These results suggest that the drying-wetting cycles are a key factor in the long-term adsorption and desorption processes under field conditions. Third, the new approach of batch desorption experiments that allow the fast and careful complete drying of soil suspensions appears to be an appropriate method to assess sorption behaviour of herbicides over a long time period.

The Mediterranean climate is characterized by a hot and dry summer where occasional storm events induce erosion and runoff. The high leaching potential of pesticides to surface waters under such climate conditions are not in relation to the main body of data that originated from summer-rain row-crop scenarios. In this 2-yr study we monitored runoff discharge and concentrations of the two soil applied herbicides diuron [3-(3,4-dichlorphenyl)-1,1-dimethylureal and simazine [6-chloro-N 2 ,N 4 -diethyl-1,3,5-triazine-2,4-diamine] from two field sites-one tilled and one no-till-cropped with grapevine (Vitis vinifera L.; Cinsault and Aramon, respectively). Despite a time lag of 140 d in 1994 between chemical application and first runoff event, diuron concentrations in overland flow exceeded 200 μg L -1 at the no-till site. In 1995 the first strong rainfall-runoff event following application carried >87 and 60% of the respective seasonal simazine and diuron loss at both sites, although it accounted for