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article in press; In silty soils under no tillage (NT), platy (P) soil structure is widespread and constrains water infiltration. Our objectives were (i) to evaluate how traffic and the presence of crop residues influence P structure developmentin the field and (ii) to characterize changes in soil structure caused by alternation of wetting and drying (w-d) periods for two topsoil layers of a silty soil and two compaction levels in the laboratory. The five-year field experiment was carried out on a Typic Argiudoll under NT and the structure of the A horizon was analyzed using visual soil evaluation (VSE) both before and five years after two traffic levels were applied to four crop sequences. The laboratory experiment of w-d cycles was carried out with two disturbed layers of a Typic Argiudoll, which was repacked to achieve two different bulk densities, and the columns were subjected to 5, 10, or 15 w-d cycles. In the field experiment, the P structure was clearly identified by VSE and corroborated by shear strength and bulk density measurements. The proportion of P structure increased until about 50% of the A horizon after 5 years, irrespective of the traffic or presence of crop residues at the expense of the F structure proportion. In the laboratory, consecutive w-d cycles caused changes in soil volume, cracking of the soil surface, and formation of P structure of variable thickness up to 20 mm, confirming that alternation of w-d periods can cause structural modification of the silty soil, in particular horizontally oriented cracks. The number of w-d cycles increased the thickness of the P structure in the upper layer (R2 = 0.55) and in the compacted treatment (R2 = 0.81). The results obtained constitute important progress in the understanding of the evolution of P structure of silty soils under NT.

article in press; The no-tillage system (NT) is widespread in the silty soils of the Argentine Humid Pampas. The aims of this study were i) to characterize the evolution of the structure of the A horizon in the northern Humid Pampas due to conversion to NT, particularly the presence of platy structure and its developmentthrough time, by taking advantage of a chronosequence since conversion to NT; and ii) to evaluate how platy structure extension in the A horizon relates to characteristics of the crop sequences and runoff in a longterm experiment. Thus, the structure of the A horizon of 25 Argiudolls with different NT history was analyzed using a visual structure evaluation (VSE) method (“le profil cultural”). Fourteen natural-rainfall erosion plots with 3.5% slope were used to analyze the relationship between the soil structural state, the crop sequence and runoff. The VSE method allowed us to understand the structure type organization of silty soils under NT, highlight the regional extent of a platy structure near the soil surface, and study its evolution and impact on runoff. All the sites analyzed exhibited a horizontal platy structure (2–10 cm thick), mainly developing on the soil surface or right under the granular structure on the soil surface. Under the platy structure, a cF structure was observed in all the sites (30–75% of the A horizon). A relationship was found between the number of consecutive years under NT and the proportion of platy structure. This evolution may result from the combination of an initial development of the platy structure and a late development of a cΓ structure from the soil surface. The results obtained during the five-year period analyzed allowed us to prove that platy structure alters the drainage pattern, restricts water entry into the soil and favors surface runoff according to its proportion in the profile of A horizon.

CT2 ; Département BAP; Leaf marker metabolites for low nitrogen stress in maize. Plant Biology Europe EPSO/FESPB 2016

International audience; The complexity of the Life Cycle Assessment (LCA) method requires many subjective choices throughout the procedure, which make decision making difficult and LCA results insecure. Our approach consists in combining life cycle thinking and sensitivity analysis to provide information to the actor of a foreground system within a product's life cycle. For any parameter of a foreground system, the trends and quantified influence on impact categories are systematically compared to determine the most effective action levers for actors controlling the process. This approach has been previously applied to a single actor, the farmer, in a case study of hemp crop production. In this study, we introduce a second life cycle actor: the industrial producer for transformation of hemp straw into insulation products for buildings. The relationships between farming and industrial actors are examined and demonstrate that industrial actors have action levers limited to climate change and energy consumption. Only a joint action of both actors can allow further reduction of climate change and energy consumption impacts. Nevertheless, the farmer action alone can allow reduction of other environmental impacts such as human toxicity or ecotoxicity.

CT3 ; EnjS4 ; Département EA; Can alternative cropping systems mitigate nitrogen losses? Results from a 17-yr experiment in Northern France. European Society of Agronomy 14 congress

CT2 ; EnjS1 ; Département BAP; Adapter la biomasse à de nouvelles valorisations – exemple de quelques graminées. Journée ASF Céréales à Paille : Débouchés alimentaires et non-alimentaires des Céréales

CT 3 ; EnjS 4 ; Département E.A. ; Modèle STICS; Modeling with STICS the effects of no-tillage vs tillage in cropping systems under constrasting pedoclimatic conditions. iCROPM 2016 International Crop Modelling Symposium

Alternative cropping systems such as conservation agriculture and organic farming are expected to decrease negative impacts of conventional systems through sequestration of organic carbon in soil and mitigation of greenhouse gas emissions. We studied soil organic carbon (SOC) dynamics in the long-term (16 years) field experiment “La Cage” (France) which compares four arable cropping systems, free from manure application, under conventional (CON), low input (LI), conservation agriculture (CA) and organic (ORG) management. Bulk densities and SOC concentrations were measured at different dates between 1998 and 2014. SOC stocks were calculated at equivalent soil mass taking into account bulk density variations and SOC redistribution across the different soil layers. We analyzed the evolution of SOC stocks and compared it with outputs of the simulation model AMG. The rate of change in SOC stocks in the old ploughed layer (ca. 0–30 cm) during the 16 years was 0.08, 0.02, 0.63 and 0.28 t ha−1 yr−1 in the CON, LI, CA and ORG systems respectively and significantly differed from 0 in the CA and ORG treatments. The AMG model satisfactorily reproduced the observed evolution of SOC stocks in the old ploughed layer in all treatments. A Bayesian optimization procedure was used to assess the mean and the distribution of the most uncertain parameters: the SOC mineralization rate and the C inputs derived from belowground biomass of cover crops which were fescue (Festuca rubra) and alfalfa (Medicago sativa). The model thus parameterized was able to predict SOC evolution in each block and soil layer (0–10, 10–20 and 20–30 cm). There was no significant difference in SOC mineralization rates between all cropping systems including CA under no-till. In particular, the increased SOC storage in CA was explained by higher carbon inputs compared to the other cropping systems (+1.72 t C ha−1 yr−1 on average). The CA and ORG systems were less productive than the CON and LI systems but the smaller C inputs derived from cash crop residues were compensated by the extra inputs from additional crops (fescue and alfalfa) specifically grown in CA and ORG, resulting in a positive carbon storage in soil. We conclude that alternative arable systems have potential to sequester organic carbon in temperate climate conditions, through higher carbon input rather than by the effect of reduced soil tillage.

L’agriculture est un contributeur important aux émissions de gaz à effet de serre (GES) en France (19 % en 2013). A ce titre, ce secteur est particulièrement sollicité pour participer à la réduction des émissions de GES de 20 % au niveau européen à l’horizon 2020. Des méthodes d’évaluation des émissions et du stockage de carbone (C) adaptées à ce secteur sont nécessaires pour guider les actions d’atténuation du bilan GES agricole. Parmi les principales lacunes actuelles, figurent la non prise en compte de la dynamique du carbone dans les sols agricoles, ainsi que la faible prise en compte de la diversité des situations agronomiques (pédo-climat et pratiques) sur un territoire.

The greenhouse gases CO2 and N2O emissions were quantified in a long-term experiment in northern France, in which no-till (NT) and conventional tillage (CT) had been differentiated during 32 years in plots under a maize–wheat rotation. Continuous CO2 and periodical N2O soil emission measurements were performed during two periods: under maize cultivation (April 2003–July 2003) and during the fallow period after wheat harvest (August 2003–March 2004). In order to document the dynamics and importance of these emissions, soil organic C and mineral N, residue decomposition, soil potential for CO2 emission and climatic data were measured. CO2 emissions were significantly larger in NT on 53% and in CT on 6% of the days. From April to July 2003 and from November 2003 to March 2004, the cumulated CO2 emissions did not differ significantly between CT and NT. However, the cumulated CO2 emissions from August to November 2003 were considerably larger for NT than for CT. Over the entire 331 days of measurement, CT and NT emitted 3160 ± 269 and 4064 ± 138 kg CO2-C ha−1, respectively. The differences in CO2 emissions in the two tillage systems resulted from the soil climatic conditions and the amounts and location of crop residues and SOM. A large proportion of the CO2 emissions in NT over the entire measurement period was probably due to the decomposition of old weathered residues. NT tended to emit more N2O than CT over the entire measurement period. However differences were statistically significant in only half of the cases due to important variability. N2O emissions were generally less than 5 g N ha−1 day−1, except for a few dates where emission increased up to 21 g N ha−1 day−1. These N2O fluxes represented 0.80 ± 0.15 and 1.32 ± 0.52 kg N2O-N ha−1 year−1 for CT and NT, respectively. Depending on the periods, a large part of the N2O emissions occurred was probably induced by nitrification, since soil conditions were not favorable for denitrification. Finally, for the period of measurement after 32 years of tillage treatments, the NT system emitted more greenhouses gases (CO2 and N2O) to the atmosphere on an annual basis than the CT system.

National audience

Agriculture, sylviculture et gaz à effet de serre : observations du réseau Ecosystèmes-Fr de l’infrastructure ICOS. Carbones atmosphériques naturels et anthropiques. Chaire Évolution du climat et de l'océan du Collège de France

Session 2; Stics et exercices internationaux d'inter-comparaison de modeles de culture. 10. Colloque Modèle de culture STICS

Poster Session 3: L3.2 Climate - smart cropping systems; The FACCE-ERA-NET+ project Climate–CAFÉ: Climate change adaptability of cropping and farming systems for Europe. Climate-Smart Agriculture 2015

Effets du travail du sol sur les cycles biogéochimiques de l'azote et du carbone : de la compréhension des mécanismes aux conséquences pour la gestion des pratiques agricoles

National audience; La baisse de la porosité, observée en système avec travail du sol réduit, peut être compensée par des phénomènes de restructuration biologiques et climatiques. Un processus plus lent qu’en conventionnel. Attention cependant aux risques de tassements profonds, peu réversibles, engendrés par des chantiers de plus en plus lourds

Labelling using the stable 15 isotope of nitrogen allows a close monitoring of the fate of the fertilizer applied to arable crops. Because 15N data give direct estimates of nitrogen transformation rates, they also provide more stringent tests for N models than those based on bulk inorganic N dynamics. They may therefore point at flaws in models that had previously gone unnoticed, especially if 15N was monitored on short time steps which capture even rapid processes like nitrification.Here we tested the simple, process-based model SUNDIAL on two such data sets obtained in Northern France under winter wheat and winter rape crops receiving various doses and forms of fertilizer N. In both experiments, microplots (≈ 1 m2 in size) within larger blocks were dressed with 2·0 atom-% enriched labelled 15N, as urea, or ammonium-nitrate as NH+4–15NO3 or 15NH+4–H–NO3. Replicate micro-plots were subsequently sampled on four occasions after fertilizer application, and 15N enrichment was monitored in plant roots and tops, and at several depths in the soil in inorganic and organic forms.Comparison between observed and simulated data showed that, shortly after application, SUNDIAL either underestimated (rapeseed) or overestimated (wheat) the rates of crop uptake. Also, the gradual incorporation of 15N into soil organic matter was too quick in autumn and too slow in spring under the rapeseed crop. The simulation of the rapid depletion of the labelled soil inorganic N pool was correct under wheat, whereas under rape, SUNDIAL predicted an accumulation of nitrate which was not observed.After a longer time interval (1–2 months), the simulated and observed amounts of fertilizer-derived N in the crop and in the soil became more comparable. However, SUNDIAL only accounted for part of the unrecovered labelled N. Additional measurements indicated that denitrification and ammonia volatilization were responsible for most of the losses, with discrepancies occurring because SUNDIAL failed to volatilize ammonia after fertilizer spreading. The other major source of error lay in the simulation of crop demand for nitrogen, which may be improved based on sounder eco-physiological concepts, such as that of a regulation of plant uptake by shoot biomass.

International audience; A technique based on progressive fumigation was used to reduce soil microbial biodiversity, and the effects of such reductions upon the stability of key soil processes were measured. Mineral soil samples from a grassland were fumigated with chloroform for up to 24 h and then incubated for 5 months to allow recolonisation by surviving organisms. The diversity of cultivable and non‐cultivable bacteria, protozoa and nematodes was progressively reduced by increasing fumigation times, as was the number of trophic groups, phyla within trophic groups, and taxa within phyla. Total microbial biomass was similar within fumigated soils, but lower than for unfumigated soil. There was no direct relationship between biodiversity and function. Some broad‐scale functional parameters increased as biodiversity decreased, e.g. thymidine incorporation, growth on added nutrients, and the decomposition rate of plant residues. Other more specific parameters decreased as biodiversity decreased, e.g. nitrification, denitrification and methane oxidation. Thus specific functional parameters may be a more sensitive indicator of environmental change than general parameters. Although fumigation reduced soil microbial biodiversity, there was evidence to suggest that it selected for organisms with particular physiological characteristics. The consequences of this for interpreting biodiversity – function relationships are discussed. The stability of the resulting communities to perturbation was further examined by imposing a transient (brief heating to 40°C) or a persistent (addition of CuSO4) stress. Decomposition of grass residues was determined on three occasions after such perturbations. The soils clearly demonstrated resilience to the transient stress; decomposition rates were initially depressed by the stress and recovered over time. Resilience was reduced in the soils with decreasing biodiversity. Soils were not resilient to the persistent stress, there was no recovery in decomposition rate over time, but the soils with the highest biodiversity were more resistant to the stress than soils with impaired biodiversity. The study of functional stability under applied perturbation is a powerful means of examining the effects of biodiversity.

International audience; L'objectif de l'article est l'analyse probabiliste du rapport coût-efficacité des pratiques agricoles encouragées par l'Union européenne pour réduire la pollution nitrique. La méthode utilisée consiste à évaluer, via une modélisation intégrée, les impacts environnementaux et économiques de différents scénarios de pratiques. Ce modèle prend en compte l'incertitude de rendement et la variabilité climatique, en vue de déterminer un scénario optimal (forte probabilité d'atteindre la norme de 50 mg/l au moindre coût). Le rapport coût-efficacité est calculé pour un bassin versant du Nord-Est de la France, pour différentes années climatiques et sous différentes hypothèses décrivant le contexte économique. Les résultats montrent que la mise en oeuvre des pratiques recommandées par l'UE ne permet pas de satisfaire rapidement la norme européenne de concentration en nitrates. Par contre, à long terme, certaines de ces pratiques permettraient une réduction significative de la pollution. Dans le cas étudié, le scénario optimal, quel que soit le contexte économique envisagé, consiste à combiner une fertilisation raisonnée et l'introduction de cultures intermédiaires pièges à nitrates. Les résultats obtenus soulignent notamment l'importante efficacité des cultures intermédiaires qui, en réduisant fortement la variabilité de la concentration de l'eau drainée, réduisent le risque de dépasser la norme environnementale. Plus largement, ils débouchent sur des recommandations afin de mieux concevoir la politique agro-environnementale.

In agriculture, differences between the kinetics of crop requirements and the rate of soil mineralization are known to affect wheat yield and quality. The high cost of organic nitrogen fertilizer may result in nitrogen availability being a limiting factor during the crop cycle. It is therefore necessary to improve fertilizer application conditions, to limit losses, to ensure that grain quality exceeds a certain threshold, and to optimize economic efficiency. The aim of this study was to improve nitrogen management in organic winter wheat crops by optimizing spring fertilization. We validated and used the Azodyn model [Eur. J. Agron. 10 (1999) 129] to determine the effect of various fertilization strategies on winter wheat production under N constraints. We first adapted the Azodyn model by constructing an organic fertilizer submodel. The resulting Azodyn–Org model was tested under several sets of conditions for the rate and timing of organic fertilizer applications, in three experiments. Preliminary results confirmed that the Azodyn model accurately predicted N soil availability in a wide range of conditions. We assessed the performance of the Azodyn–Org model for predicting grain yield, grain protein content and mineral N in the soil. We found that grain yield was correctly predicted whereas grain protein content was slightly overestimated. Thus, the Azodyn–Org model has potential for use as a decision-making tool for managing spring N fertilization in organic wheat crops.

One part of the collected bottle glass cannot be recycled because small fragments cannot be separated from organic matters and metal residues. One possible way of getting rid of this unrecycled glass is to incorporate it into the ploughed layer of the soil. The incorporated glass fragments will alter the physical state of the soil, particularly the seedbed. We studied the consequences of such a change in soil physical properties on sugar beet emergence in laboratory experiments and using a model for estimating the effects on emergence under more realistic sowing conditions. We examined the effects of fine (

Herbage yield of alfalfa (Medicago sativa L.) depends on forage management or environmental conditions that change C and N resource acquisition, and endogenous plants factors such as root organic reserves and number of active meristems. The aim of this work is to study the influence of two sowing dates in summer (12 July or 9 August), N fertilization (0 or 100 kg ha � 1 ) anduor irrigation applied during the first year of alfalfa establishment on (i) the accumulation of N organic reserves (soluble proteins and more specifically vegetative storage protein) in taproots during autumn, (ii) the number of crown axillary meristems present at the end of winter and (iii) the dynamics of spring shoot growth. Delaying the sowing date for one month reduced root growth and root N storage, especially vegetative storage proteins (VSP) during autumn. Irrespective of sowing dates, N fertilization did not affect root biomass, number of crown buds, total root N, root soluble protein or VSP concentrations. By contrast, water deficiency during alfalfa establishment in the early summer reduced both root growth and N reserve accumulation. When spring growth resumed, there is a significant linear relationship between leaf area development and soluble protein and VSP concentrations in taproots, and also the number of crown buds. The results showed that an early sowing date and adequate water status during the summer allowed alfalfa plants to accumulate N reserves by increasing taproot mass and soluble protein concentrations, especially VSPs. This resulted in rapid shoot regrowth rates the following spring.

Functional traits distribution as causal link between environmental pressure (local climate and cropping systems) and soil invertebrate abundance. The 1st Global Soil Biodiversity Initiative conference (GSBI)

Amongst the biodiversity components of agriculture, weeds are an interesting model for exploring management options relying on the principle of ecological intensification in arable farming. Weeds can cause severe crop yield losses, contribute to farmland functional biodiversity and are strongly associated with the generic issue of pesticide use. In this paper, we address the impacts of herbicide reduction following a causal framework starting with herbicide reduction and triggering changes in (i) the management options required to control weeds, (ii) the weed communities and functions they provide and (iii) the overall performance and sustainability of the implemented land management options. The three components of this framework were analysed in a multidisciplinary project that was conducted on 55 experimental and farmer’s fields that included conventional, integrated and organic cropping systems. Our results indicate that the reduction of herbicide use is not antagonistic with crop production, provided that alternative practices are put into place. Herbicide reduction and associated land management modified the composition of in-field weed communities and thus the functions of weeds related to biodiversity and production. Through a long-term simulation of weed communities based on alternative (?) cropping systems, some specific management pathways were identified that delivered high biodiversity gains and limited the negative impacts of weeds on crop production. Finally, the multi-criteria assessment of the environmental, economic and societal sustainability of the 55 systems suggests that integrated weed management systems fared better than their conventional and organic counterparts. These outcomes suggest that sustainable management could possibly be achieved through changes in weed management, along a pathway starting with herbicide reduction.

Acyrthosiphon pisum Harris (Aphididae: Hemiptera), the pea aphid, is an important pest in organic farming systems. In this work, the objective was to gather empirical field data on the associational resistance of durum wheat–winter pea intercrops towards the pea aphid, compared with pure stands of winter pea. Our results showed that intercropping winter pea with durum wheat significantly decreased A. pisum abundance in all the situations. Moreover, it was systematically observed that pea grew bigger in pure than in intercropped stands but after considering pea dry mass as a covariate, it appeared that the durum wheat–winter pea intercrop was still significantly less attacked by pea aphids than the sole crop. Intercrop sowing designs had an incidence on infestation levels: substitutive diversification systems of different types are more effective in decreasing the level of aphid infestation than does the additive system. In addition, substitutive row intercrop is significantly less infested than substitutive mixture. These results suggest that a mechanism related to the resource concentration hypothesis may explain the associational resistance of the IC of durum wheat–winter pea towards A. pisum.

La structure du sol : impact du travail du sol. Faut t’il travailler le sol ?

International audience; An experimental and modelling study of source-sink interactions in Vitis vinifera L., cv. Cabernet Sauvignon, rooted cuttings under non-limiting environmental conditions with a 12 h photoperiod is presented here. After 4 h, measured photosynthesis, stomatal conductance and leaf carbohydrate content reached maximum values. Over the remainder of the photoperiod, photosynthesis and stomatal conductance decreased continuously, whereas leaf carbohydrate content remained relatively constant. Because the experiment took place in a non-limiting environment, the results suggest that stomatal regulation of photosynthesis was mediated by an internal factor, possibly related to sink activity. A simple I-source, 2-sink model was developed to examine the extent to which the data could be explained by a hypothetical sink-to-source feedback mechanism mediated by carbohydrate levels in either the mesophyll, the source phloem or the phloem of one of the two sinks. Model simulations reproduced the data well under the hypothesis of a phloem-based feedback signal, although the data were insufficient to elucidate the detailed nature of such a signal. In a sensitivity analysis, the steady-state response of photosynthesis to sink activity was explored and predictions made for the partitioning of photosynthate between the two sinks. The analysis highlights the effectiveness of a phloem-based feedback signal in regulating the balance between source and sink activities. However, other mechanisms for the observed decline in photosynthesis, such as photoinhibition, endogenous circadian rhythms or hydraulic signals in the leaf cannot be excluded. Nevertheless, it is concluded that the phloem-based feedback model developed here may provide a useful working hypothesis for incorporation into plant growth models and for further development and testing.

A high-temperature catalytic oxidation (HTCO) method was evaluated and compared with the Kjeldahl method for determining total dissolved N (TDN) in 0.025 M K 2 SO 4 soil extracts used to assess soil microbial biomass nitrogen. First the HTCO method was evaluated for routine analysis for TDN in K 2 SO 4 solutions. Nitrogen recoveries measured by HTCO exceeded 98% for compounds containing organic and inorganic N and for concentrations up to 10 mg N l −1 . The proposed indirect injection of sample into the furnace safeguards the catalyst and quartz combustion tube. In these conditions, the drift of signal sensitivity during sequence analysis was negligible implying that HTCO can be used for the routine analysis of samples in a 0.025 M K 2 SO 4 matrix. The HTCO and Kjeldahl methods were then compared for determining soil microbial biomass nitrogen in different types of soil using the fumigation-extraction method. The TDN concentrations in K 2 SO 4 soil extracts measured with both methods were well correlated. Some discrepancies however, were, observed for TDN concentrations >10 mg N l −1 due to a probable underestimation of N in the soil extracts with the Kjeldahl method. The calculated extractable microbial biomass values resulting from the difference in TDN between control and fumigated soils were in good agreement for both methods. HTCO thus provides a very rapid and reliable method for measuring TDN in K 2 SO 4 soil extracts used to determine soil microbial biomass nitrogen.

There is considerable discussion about the influence of soil management techniques on soil erosion, water use and conservation, and more recently carbon dioxide sequestration and waste disposal. The soil–atmosphere interface, particularly the seed bed layer is of particular concern to agronomists and soil scientists because it is the focus of the physical processes affecting crop establishment and biological activity. This paper evaluates the current knowledge (1) in modeling seedling emergence and residue decomposition, (2) seedbed structure and its resulting physical conditions, and (3) tillage operations affect on seedbed structure and residue distribution.

A model predicting seedling emergence is described and applied to sugarbeet (Beta vulgaris L.). The input variables are the soil surface texture, soil temperature, rainfall, aggregate size distribution and position in the seedbed, sowing depths, characteristics of the seeds (initial seed mass distribution, germination time, and hypocotyl elongation distributions). A three-dimensional seedbed layer is created where the aggregates and seeds are placed. Soil water content is assumed not to limit sugarbeet emergence (sowing conditions in northern Europe). The time needed to reach the soil surface is calculated using germination thermal time, soil temperature, the presence or absence of aggregates, and the hypocotyl elongation function. The ability of seedlings to break through the soil surface is a function of crust development and moisture. The seedling growth after emergence is calculated with reference to seed mass distribution, emergence delay, and the presence or absence of mechanical obstacles. The emergence prediction was tested in field experiments with four seedbeds, from fine earth to cloddy structure, and a sowing depth of 17 to 35 mm. The predicted number and sizes of clods encountered by seedlings and the calculated hypocotyl length were not significantly different from measured ones. Predicted germination times were longer than the observed ones (differences

Because of their high content in heavy metals, Fe–Mn concretions present in soils can be a source of release of trace metals in the environment. Metal-rich concretions were isolated from a top horizon of a Rendzic Lithosol developed on limestones in France. The distribution of metallic elements (Cr, Co, Ni, Cu, Zn, Pb) was studied at different scales: field sampling, isolated concretions, and individual particles. Methods of investigation combined bulk chemical analysis, optical microscopy, X-ray diffraction (XRD) and microanalysis using scanning and transmission electron microscopes. The concretions are constituted by concentric rings and contain quartz, feldspars, kaolinite, mica, goethite, and Ti oxide as crystalline phases. A strong heterogeneity in the chemical composition is evidenced at all different scales. The total composition of different populations of Fe–Mn concretions depends on field sampling. Metals are detected at the micrometer and nanometer scales with variable frequencies, occurrences reflecting the abundance of metal-bearing components and the size of metal clusters. Statistical treatments of microanalytical data show marked trends. A strong positive correlation of Mn (and to a lesser extent of Ca) with Ni, Zn, (and to a lesser extent with Co and Cu) indicates trace metals to be associated with poorly crystallized Mn–Ca-rich areas. The correlation of Pb with Fe and P suggests its incorporation in an Fe-rich phosphate component. No correlation of metals with well crystallized silicates, Fe-sesquioxides or sulfate minerals is established. Cr was diffusely distributed.

The isotopic composition of lead: a useful tool to estimate the distribu- tion of exogenous and natural lead in soils. Pb isotopic ratios were analysed in soil horizons and in grain size fractions of two soils, with contrasting pedogenesis. For an andosol, the results highlighted a progressive distribution of exogenous Pb with depth and, at the scale of the soil constituents, an increasing incorporation of exogenous Pb with decreasing particle size. For a podzol, the distribution of exogenous Pb was linked to the dynamics of the organic matter. In the BPh horizon, the 100-200 µm fraction was found to be a predominant soil compartment accumulating exogenous Pb ascribed to the precipitation of Pb on organic compounds around quartz grains. © 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS

International audience; Irrigation non-uniformity is a key factor in reducing water and N efficiency and increasing N leaching. This study simulates the impact of non-uniform irrigation on crop growth and associated nitrogen fluxes. Simulations were applied to a travelling gun irrigation system on a maize crop over a 21-year period. Cropping and intercropping periods were analysed for two fertilisation rates (180 and 280 kg N$\cdot$ha$^{-1}$). The spatial coefficients of variations over a period of 21 years were below 37, 8, 25 and 34% , for N uptake, mineralised N, inorganic N left in the soil at harvest and leached N, respectively. Simulations with or without reinitialization every year of inorganic N and water content at sowing gave similar results, except in specific years. Differences between high and low fertilisation treatments showed up especially for leaching. Other irrigation and fertilisation strategies should be further analysed to provide more general conclusions.; Modélisation des conséquences agronomiques et environnementales d'une irrigation non uniforme sur une culture de maïs. I. Bilan azoté. L'hétérogénéité de l'irrigation est un facteur important de réduction de l'efficience de l'eau et de l'azote, et d'augmentation du lessivage. Ce travail simule l'impact de l'hétérogéneité de l'irrigation sur la croissance et les flux azotés d'une culture de maïs irriguée au canon. L'analyse porte sur 21 ans et sépare les périodes de culture et d'interculture. Deux niveaux de fertilisation sont analysés (180 and 280 kg N$\cdot$ha$^{-1}$). Les coefficients de variation spatiaux sur les 21 années sont inférieurs à 37 % , 8 % , 25 % , et 34 % , pour l'azote absorbé, l'azote minéralisé, le reliquat azoté à la récolte, et l'azote lixivié. La réinitialisation ou non du stock d'eau et d'azote au semis d'une année à l'autre a peu d'effets, sauf pour 2 années particulières. Des différences existent entre les 2 niveaux de fertilisation, notamment pour l'azote lessivé. D'autres stratégies d'irrigation et de fertilisation devraient être analysées pour tirer des conclusions générales.

During the drainage season, significant quantities of suspended matter can be exported from a drain collector. Their nature has been determined with a methodology linking chemical analysis, X-ray diffraction, and electronic microscopy associated with image analysis. The majority of these particles are smaller than 200 nm. They are composed of 2:1 phyllosilicates and iron particles usually in amorphous form. 137 Cs, phosphorus and organic matter clearly demonstrate the superficial origin of these particles. Drainage modifies natural leaching of soil by exporting definitively particles from the soil profile.

In temperate environments, the total dry matter (TDM) of a crop is closely related to the amount of photosynthetically active radiation absorbed (ΣPARa), as long as other factors (water, nutrients, . . .) are non-limiting. For oilseed rape crops, many authors have shown that the radiation use efficiency (RUEa) varies within a wide range, from 1 to 4 g MJ−1 of ΣPARa according to developmental stage and environmental conditions. In order to explain this variability, effects of N and temperature on RUEa were investigated during a 1-year field experiment involving three N treatments (N fertilisation rates: 0, 135 and 270 kg ha−1). Leaf, flower, and pod surface areas, as well as the DM and N content of the various plant parts were measured every 2–4 weeks for 17 sampling dates from emergence to harvest. RUEa was calculated from total generated DM (shoot and root DM, plus that of dead leaves fallen to the ground). Daily PARa was calculated using a 3-layer model taking into account leaf and pod absorption and reflection of PAR by flowers and soil. The N nutrition index (NNI) proposed by Lemaire and Gastal (1997) was used to evaluate the N effect on RUEa. NNI was significantly higher than the critical N value (meaning that N was non-limiting) for the N270 treatment from emergence to pod formation, but N deficiency occurred with N0 at the 12-leaf stage and later with N135 at flowering. The maximum possible RUEa (RUEamax) was assumed to be the value obtained with the treatment N270, where N was non-limiting. The N deficiencies which occurred for N0 and N135 significantly reduced the green LAI and PAI, and consequently ΣPARa. To remove any effect other than N on the RUEa, the ratio of actual to maximum RUEa (RUEa/RUEamax) proposed by Belanger et al. (1992) was calculated for each developmental stage of oilseed rape. A linear regression fit well (R2=0.919; 8 d.f.) the response of RUEa/RUEamax versus N deficiency, for values of NNI lower than 1. The resulting equation was the following: RUEa/RUEamax=0.74×NNI+0.23. RUEamax was also significantly affected by developmental stage. Whereas the corresponding changes in RUEamax from the 6-leaf stage to the end of flowering could be related to air temperature, there was evidence of a developmental effect in the other stages. RUEa was lower in the early stages (emergence to 5–6 leaves), and from pod formation until ripening; the latter decrease could be attributed to the high energy cost of lipid biosynthesis.

Investigations have been initiated to develop a sufficiently good separation of both major and minor organic acids and inorganic anions present in grape musts using a Dionex As11 column, a sodium hydroxide gradient elution and a suppressed conductivity detection. Separation was complicated in aqueous mobile phase by co-elutions and selectivity was optimized using organic modifiers that alter ion-exchange selectivity for hydrophobic ions. In this study, the influence of three different solvents (methanol, ethanol and acetonitrile) on the efficiency of column was compared. The best separation of all ions in a synthetic solution was achieved with an eluent containing 13% (v/v) methanol and 13% (v/v) ethanol in water, the run during only 20 min. This method was next applied to grape juices with success and has shown sensitivity and reproducibility. Moreover, sample preparation was a simple 20-fold dilution with 0.45 microm filtration and direct injection without prior sample clean-up.

The objective of this study was to compare the effects of different dewatering processes on the phosphorus (P) availability of an FeCl3-precipitated and lime-conditioned sludge having an initial dry matter content (DMC) of 4%. The sludge was dewatered by either drying (D), freezing/ thawing (FT) or centrifugation (C) until a DMC of about 15% was reached. Thereafter the FT and D sludges were gently dried to obtain a DMC increasing up to 50 to 60%. The plant-available sludge P was assessed by the change in the isotopic dilution of P taken up by ryegrass (Lolium perenne [L]) after sludge amendments to one soil. After the plant experiment, the soil-to-solution transfer of P ions and bicarbonate-and ammonium lactate-extractable P were determined in selected soil samples. The amount of plant-available P (L-value) and the contribution of sludge P to plant nutrition (% Pdfsl) in soil amended with non-dewatered sludge (ND) were not significantly different from the L and percentage Pdfsl values of soils amended with FT, D and C sludges. Nor did the subsequent drying of D and FT sludges significantly change the L and percentage Pdfsl values. Hence, the dewatering processes did not significantly alter the initial sludge P availability. The soil-to-solution transfer of P ions and the chemically extracted P did not significantly differ between the different sludge-amended soil samples. The percentage Pdfsl values can be predicted by percentage Δ E1, since the overall average relative increase (%Δ E1) in the immediate soil-to-solution transfer of P ions did not significantly differ from the percentage Pdfsl values.

International audience

A practical model of the soil structure dynamics in ploughed fields can be a powerful aid to farmers attempting to optimise their management practices. This paper describes a compartmental model that simulates the changes over several years in an indicator of the effects of cropping systems on soil structure. This indicator, the proportion of severely compacted clods in the ploughed layer, was measured in two plots at the INRA Experimental Centre at Grignon (Yvelines, France), where two cropping systems produced very different compaction conditions in a silt loam. The ploughed layer was considered to be a set of elementary compartments delimited by the wheel tracks and actions of tillage tools. The percentage of severely compacted clods in each elementary volume changed with time due to transfer between compartments during mouldboard ploughing, compaction and fragmentation. The proportion of severely compacted clods changed exponentially until it reached a plateau, after about 8 years. The equilibrium values of the indicator were very similar to.those measured in the experimental plots. The model was very sensitive to the rate at which severely compacted clods were lost, probably because the vertical distribution of these clods in the soil profile was not taken into account in this compartmental model. The model in its present state can be used to compare the effects on soil structure of various technical changes.

In this study, the implications of water loading into the central channel of the plasma were considered when an ultrasonic nebulizer (USN) associated with desolvation was used in axial-view inductively coupled plasma atomic emission spectrometry. The effects have been characterised during cadmium analysis in the presence of various environmental matrix types. Interferences occurred as a result of changes in the sample introduction system. Signal suppression was observed for the highest water loading. Conversely, signal enhancement occurred for the lowest water loading. The desolvation of aerosols in USN saved the plasma a lot of energy but influenced the excitation conditions by changing the thermal environment of the plasma. From the results shown in this paper, it was clear that the behaviour of a solvent removal system depended on the operating conditions used (concentration of matrix, temperature heating and cooling and especially carrier gas flow rate). Under a rigorous choice of these factors according to the nature of the sample matrix, the interferences could be minimised. The plasma characteristics dependent on the concentration of water have also been evaluated with the diagnostic MgII/MgI line intensity ratio, which confirm the previous results.

This paper discusses the time-dependent mechanical response of poly(methyl methacrylate) (PMMA) and polystyrene (PS) subjected to a shallow indentation made by a 750 µm radius steel ball at 25 °C. The penetration depth was measured as a time-response to a prescribed loading history of the indenter. The tests were performed in the intermediate elastic-plastic regime, which is of paramount importance when dealing with the mechanics of a multicontact interface between rough bodies. The creep characteristics under constant load were analysed with an Eyring law relating the average stress and the strain rate in the deformed volume. The results were compared to data obtained by a standard uniaxial compression test on the bulk material. We have deduced a simple empirical rule which accounts for the heterogeneous stress and strain fields under the indenter and reduces the intricate problem of elastic-plastic indentation creep to an effective scalar rule.

Amorphous aluminosilicates were synthesised at two different initial reagent concentrations. Depending on the concentration used, the final reaction products were identified as either imogolite or allophane. In millimolar medium (millimolar Al initial concentration and Al/Si=2), imogolite precursors are synthesised during hydrolysis and condensed by heating to build up imogolite tubes. In decimolar medium, precursors with varying local structures are synthesised and condense upon heating to build up allophanes spheroids aggregates. In each medium, silica gel coprecipitated in proportions less than 10% in mass, which seems to have only a weak influence on aluminosilicate synthesis. The zero point of salt effect of suspensions of imogolite, allophane and their respective precursors were determined, and the affinity of these four products towards Cd 2+ , Cu 2+ and Pb 2+ was studied. For imogolite and for both precursors, Cu 2+ and Pb 2+ adsorption can be described as specific, whereas Cd 2+ adsorption is only electrostatic. The three metallic cations display specific adsorption towards allophane suspensions.

We report an extensive study of dynamic friction at nonlubricated multicontact interfaces between nominally flat bodies, rough on the micrometer scale, made of identical polymer glasses. This work, which complements a previous study of static friction on the same systems, has been performed at temperatures ranging from $20\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ to close below the glass transitions. The data are analyzed within the framework of the Rice-Ruina state- and rate-dependent friction model. We show that this phenomenology is equivalent to a generalized Tabor decomposition of the friction force into the product of an age-dependent load-bearing area and of a velocity-strengthening interfacial shear stress. Quantitative analysis of this latter term leads to associate velocity strengthening with thermal activation of basic dynamical units of nanometer dimensions. We interpret our results with the help of a model due to Persson, in which shear is localized in a nanometer-thick interfacial adhesive layer, pinned elastically at a low shear level. Sliding proceeds via uncorrelated depinning of ``nanoblocks'' which constitute the layer. It is the competition between the drive-induced loading of these blocks up to their depinning stress and the thermally activated premature depinning events which leads to the velocity-strengthening contribution to the interfacial strength. In our interpretation, friction therefore appears as the localized elastoplastic response of a confined amorphous interfacial layer.

cept light was severely reduced so that root growth was finally reduced. Effects on leaf growth, biomass accumulation and root morphogenesis associated with the establishment of Key words: Zea mays L., maize, phosphorus, root, root phosphorus (P) deficiency were studied on maize in morphogenesis. order to test the hypothesis that the root system response can be accounted for by the effect of P

A dynamic soil–crop model was developed to predict the date on which N deficiency occurs for winter wheat crops in the temperate climate of Northwest Europe. It is based on the daily simulation of soil N supply and crop N requirement for the period during which N-fertilizer is usually applied to wheat crops, the end of winter until flowering. The soil sub-model was derived from the `balance-sheet method' used in France for nitrogen fertilization recommendations. It describes the net mineralization of various sources of organic matter (soil humus, crop residues, organic products). The crop sub-model simulates crop biomass production and its nitrogen content using a radiation use efficiency model and a critical dilution curve for nitrogen content. Both soil and crop sub-models require few parameters and inputs, most of which are readily available on commercial farms, together with daily climatic data. The model tested with various rates and timings of N application in three experiments accurately simulated the date on which nitrogen deficiency began in wheat crops. The interest in using the model for tactical and strategic approaches is discussed.

Within the framework of the GCTE Soil Erosion Network the Limburg Soil Erosion Model (LISEM) has been tested and validated in two catchments in South-Limburg (the Netherlands) and Zululand (South Africa). The calibration and validation of the Green–Ampt version of the LISEM model using 10 storms from the Catsop catchment in the Netherlands shows that differences in measured and simulated hydrographs and sediment loads can be large. These differences may be caused by the sensitivity of the model to some of the input variables, such as saturated hydraulic conductivity and the initial soil moisture content. Given the uncertainty in the input maps of these variables and a limited number of point data that is used to create these maps, a large part of the differences between measured and simulated data can be explained by these uncertainties. Thus, it is clear that detailed process-based models such as LISEM require very detailed and high-resolution input data in order to produce quantitative reliable results. The runoff processes in the Zululand catchment appeared to be dominated by slow throughflow and groundwater flow, which are processes that are not incorporated in LISEM.

Summary The capacitance probe is an attractive device for monitoring soil moisture automatically. However, its sphere of influence is rather small (a few cubic centimetres only). We have analysed the possibility of monitoring moisture at the field scale using only a few probes (≤3). We calibrated each probe by establishing a direct relation between the field average soil moisture θf and the signal given by the probe. As in earlier studies, we found that a linear relation is generally suitable. A classical statistical analysis was performed to assess the error of a single probe. When replicate probes were installed, we obtained replicate estimates of θf. We proposed an estimator θf that combines all replications optimally. Three experiments each lasting several months were carried out on bare tilled fields to evaluate the probe against gravimetric measurements. Our results show that the calibrations differ significantly from one probe to another. Once calibrated, the capacitance probe provided accurate soil moisture measurements (70% of the calibration relations had residual standard deviations < 0.02m3m−3), but it is advisable to have at least two replicate probes. Soil water storage was well estimated by combining four to seven probes to establish the moisture profile, despite the error induced by each probe. Moreover, the temporal variations in water storage were accurately measured by the probes. We found an error of 0.6 mm day−1 (standard deviation) in daily variation of the water storage, which partly involved the error made on the reference measurements (gravimetric method).

ˇ and organic N). This fit validated the compartmental model and enabled calculation of six N fluxes: mineralisation (m), ammonium immobilisation (ia), nitrate immobilisation (in), nitrification (n), volatilisation (v) or denitrification (d) and remineralisation of recently immobilised N (r). Sensitivity analysis indicated that the classical assumptions of exclusive ammonium immobilisation (in=0) and absence of N remineralisation (r = 0) had to be rejected. NH4 immobilisation appeared to be dominant when ammonium and nitrate were both present, but was not exclusive: a Langmuir-type relationship could be established between the immobilisation ratio ia/(ia+in) and the molar ratio of soil N concentrations NH4 + /(NH4 + +NO3 ˇ ). Remineralisation of N occurred simultaneously with immobilisation during wheat straw decomposition and represented 7‐18% of gross immobilisation. Taking into account small gaseous losses, volatilisation or denitrification, allowed a better fit to be obtained between observed and simulated N and 15N pools. Nitrification was better described by first order than by zero order kinetics. The eventuality of direct assimilation of organic N by microbial biomass or N humification could not be determined but had no significant influence on the calculation of other fluxes. When FLUAZ was applied to a single treatment (NH4 labelled), it also gave a good fit but only m, i (=ia+in), n, v or d could be determined. The mineralisation and immobilisation rates were slightly lower than those found with the paired treatments: this diAerence was mainly due to the hypothesis r = 0 and disappeared when r was fixed at the value

In winter crops, leaf area is a major determinant of the final yield, and is substantially affected by losses occurring during vegetative growth. Here, we propose and test a submodel simulating the development of leaf area and pod area, along with leaf senescence, for winter oilseed rape (Brassica napus L.), which was included in a CERES-type model for rape adapted from CERES-N Maize. This crop model, called CERES-Rape, has components for crop phenology, net photosynthesis, N uptake, and assimilate partitioning. As a new feature compared to previously published work, the leaf area submodel includes senescence from shading due to competition for light in the canopy, and from leaf N deficiencies. The model has been developed and parameterised on a 1-yr-long experiment with three fertilizer N treatments in northeastern France, during which measurements of senescing parts allowed calibration of the equations for leaf area index (LAI) senescence and total generated LAI. The leaf area submodel, once coupled to the CERES-Rape model, was tested against two additional experiments from Denmark and northern France. This process-oriented submodel proved accurate for the simulation of actual LAI whether in the calibration or in the validation phase, with an overall Root Mean Square Error (RMSE) of 0.496 m2 m−2, falling close to the mean experimental standard deviation. Extrapolation did not require any further adjustment, although a different cultivar was involved.