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The mechanisation of forestry operations is too recent in France to have enough perspective and scientific knowledge of the effects on extensively managed soils. Two experimental sites on soils sensitive to compaction (silty acidic soils laying on top of a clayey subsoil) were set in Lorraine (France). A gentle and controlled compaction of these physically very analogous soils was carried out during spring 2007 at the Azerailles site (AZ) and during spring 2008 at the Clermont-en-Argonne site (CA). Immediate changes were observed for all ecosystem physical, chemical and biological functioning indicators. Soil restoration dynamics were followed using continuous monitoring of numerous parameters, including soil moisture and occurrence of a perched water table (PWT) (monitored at a daily time step) and PWT chemistry (monthly time step). Mid-term monitoring (7–8 years) results showed that both soils shifted towards a hydromorphic soil type attested by the increase in PWT frequency and duration, which invaded the soil upper layers, leading to characteristic Fe, Mn and S mobility and a change in organic compounds stability. Though soil types were very similar, the PWT characteristics varied notably between both sites. The mean residence time of the PWT was shown to be a major driver of its geochemistry, but with strong interaction with soil characteristics. A previous study made on both sites suggested that soil clay content and clay mineralogy controls the PWT dynamics through effects on aggregation. From a PWT perspective, seven years of monitoring were insufficient to observe any soil compaction recovery in the richer soil of AZ but a partial recovery was observed for the chemically poorer soil (CA). Compaction durably impacted the two studied soils and the probability that a new compaction event may occur before the complete recovery from the first disturbance must be considered in forest management.

International audience; Le changement d’usage des terres et l’impact de l’anthropisation sur les milieux forestiers tropicaux sont en progression constante sous les tropiques et en Guyane française. Ces changements sont souvent accompagnés de défriches mécanisées qui favorisent la compaction du sol. Notre objectif était de suivre l’évolution de la compaction du sol d’une parcelle de forêt naturelle exploitée (7 ha) soumise à une défriche mécanisée alternative (itinéraire « chop and mulch », couvert herbacé de Stylosanthes guianensis), puis replantée de quatre espèces forestières commerciales. Sur cet espace présentant finalement diverses couvertures de sol (sol nu, mulch, couvert herbacé), nous avons mesuré la densité apparente jusqu’à 30 cm de profondeur et effectué le test d’infiltration simplifié de Beerkan lors de trois campagnes : avant, juste après et neuf mois après la défriche. Avant la défriche, les sols avaient une très bonne capacité d’infiltration (111 cm/h), étaient peu denses à 0-5 cm de profondeur (0,88) et denses à 5-30 cm (1,19 à 1,40). Juste après la défriche, les sols avaient une capacité d’infiltration très réduite (2 cm/h) et leur couche de surface avait été fortement compactée (1,28) contrairement aux couches plus profondes (1,41 à 1,49). Neuf mois après la défriche, les sols avaient retrouvé une très bonne capacité d’infiltration (149 cm/h), particulièrement sous le couvert herbacé de S. guianensis, et leur couche de surface avait retrouvé une densité proche de l’état initial (1,01), contrairement aux couches plus profondes (1,46 à 1,58). De futures recherches sont nécessaires pour expliquer le retour rapide à l’état initial de la couche de surface et estimer la contribution relative de la macrofaune du sol, des racines et de la fissuration.

Soil is a critical natural resource and the most biologically active compartment of the biosphere. Soils support global agriculture and forestry and they host hydrological processes largely controlling the recharge of the world's groundwater resources. Soil structure or architecture, referring to the binding and arrangement of soil constituents, is an important trait that supports a wide array of soil hydro-ecological functions. Despite its importance, soil structure remains difficult to define and characterize particularly at scales relevant to field applications. Typically, soil structure characterization relies on laboratory measurements on core samples or on episodic small scale field measurements, offering limited perspectives on the spatial and temporal variations of soil structure. The motivation of this thesis rests on the need for characterization techniques that provide soil structure information at relevant spatial scales (e.g., for applications in agricultural operation and management) and can guide strategies to maintain favorable soil structure. Thus, the main objective of this thesis is to evaluate the potential of harnessing geophysical methods to fill the scale-gap in characterization of soil structure and to propose a way forward in using geophysical methods to characterize soil structure directly (via impact of soil pores, transport and mechanical properties on geophysical signals), and indirectly by measurement of surrogate variables (wetness, rates of drainage). First, we identify the geophysical methods that hold the largest potential for characterizing soil structure-related mechanical and hydraulic states. For this, we chose the seismic method for its unmatched sensitivity to the soil mechanical traits and the Direct Current (DC)-resistivity method for its robustness and known sensitivity to the soil water content and pore network characteristics. We present advances on integrative frameworks combining field monitoring and physically-based modeling of seismic and geoelectrical signatures that enable interpretation of measured signals in terms of soil structure. These frameworks were tested at the Soil Structure Observatory (SSO) experimental field site, located in the vicinity of Zürich, Switzerland. The SSO is a long-term experiment designed to study the evolution of soil properties following a compaction event in the spring of 2014. We monitored geophysical data at the SSO focusing on four experimental plots: non-compacted and compacted bare soil and non-compacted and compacted ley. We developed a new pedophysical model to interpret macroscopic seismic properties in terms of soil structure. Based on soil rheology models, our pedophysical model captures subtle soil mechanical signatures by accounting for soil plastic deformation during compaction events. This pedophysical model is used to interpret P-wave velocities monitored in the spring and summer of 2019. The monitored P-wave velocities carried a strong imprint of soil compaction and were roughly 30% higher for compacted soils than for non-compacted soils. The P-wave velocities were well predicted using the contact area between aggregates as the main characterizing feature differentiating soil structure. The model inferred contact areas between aggregates that are 2.9 times larger for compacted than for non-compacted soils. We monitored DC-resistivity data in the spring and summer of 2018. In order to interpret these data, we developed a modeling scheme that combines a new pedophysical model of soil electrical properties and a one-dimensional water flow and heat transfer model. This framework includes a soil-structure specific evaporation model. Raw DC-resistivity data revealed that soil compaction leads to a persistent decrease in soil electrical resistivity (~15%). These differences are well reproduced by our proposed pedophysical model by invoking a reduction of macroporosity and its connectivity by the compaction event. Time-Domain Reflectometry (TDR) and DC-resistivity data revealed that compacted soils (both bare soil and ley) are typically drier (i.e., present greater water losses) than non-compacted soils. To explain this, we invoke differences in evaporation properties to qualitatively reproduce differences in water storage between compacted and non-compacted soils. The monitored seismic and geoelectrical data suggest that soil properties have not yet recovered from compaction. The research reported here is a first step for harnessing geophysical methods to address a long standing challenge of soil structure quantification to inform agronomic activities, diagnose chronic soil degradation (compaction) and help calibrate Land Surface models that rely on currently incomplete soil information. Most importantly, the thesis provides a blueprint for future integration of geophysics and soil research through combined monitoring and modeling., Le sol est une ressource naturelle essentielle et le compartiment biologique le plus actif de la biosphère. Les sols sont les supports de l'agriculture et de la sylviculture, et ils abritent des processus hydrologiques qui contrôlent en grande partie la recharge des eaux souterraines. La structure ou l'architecture du sol, c'est-à-dire, la liaison et la disposition des constituants du sol entre eux, est un paramètre important pour les fonctions hydro-écologiques du sol. Malgré son importance, la structure du sol reste difficile à caractériser, en particulier à des échelles pertinentes pour les applications sur le terrain. Typiquement, la caractérisation de la structure du sol est faite à partir de mesures en laboratoire sur des échantillons de sol ou de mesures ponctuelles épisodiques, ce qui offre des perspectives limitées sur les variations spatiales et temporelles de la structure du sol. La motivation de cette thèse repose sur le besoin en techniques de caractérisation pour fournir des informations sur la structure du sol à des échelles spatiales pertinentes pour l'exploitation agricole et pour guider des stratégies de maintien de structure de sol favorable. Ainsi, l'objectif principal de cette thèse est d'évaluer le potentiel de l'utilisation des méthodes géophysiques pour la caractérisation de la structure du sol, soit directement (via l'impact des pores du sol, du transport et des propriétés mécaniques sur les signaux géophysiques), soit indirectement par la mesure de variables de substitution (humidité, taux de drainage). Premièrement, nous avons identifié les méthodes géophysiques qui présentent le plus grand potentiel pour caractériser les états mécaniques et hydrauliques liés à la structure du sol. Pour cela, nous avons choisi la méthode sismique pour sa sensibilité inégale aux caractéristiques mécaniques du sol et la méthode de résistivité en courant continu pour sa robustesse et sa sensibilité connue à la teneur en eau du sol et aux caractéristiques du réseau poreux. Nous présentons des avancées sur les approches intégratives combinant le suivi de données sur le terrain et la modélisation physique des signatures sismiques et géoélectriques qui permettent l'interprétation des signaux mesurés en termes de structure du sol. Ces systèmes ont été testés sur le site expérimental du Soil Structure Observatory (SSO), situé à proximité de Zurich, Suisse. Le SSO est un site d’études expérimentales sur le long terme conçu pour étudier l'évolution des propriétés du sol après un événement de compactage qui a eu lieu au printemps 2014. Nous avons collecté des données géophysiques au SSO en nous concentrant sur quatre parcelles expérimentales: sol nu non compacté et compacté, sol herbeux non compacté et compacté. Nous avons développé un nouveau modèle pédophysique pour interpréter les propriétés sismiques macroscopiques en termes de structure du sol. Basé sur des modèles de rhéologie du sol, notre modèle pédophysique capture les signatures mécaniques subtiles du sol en tenant compte de la déformation plastique du sol lors des événements de compactage. Ce modèle pédophysique est utilisé pour interpréter les vitesses des ondes P mesurées durant le printemps et l'été 2019. Les vitesses de l'onde P observées portaient une forte empreinte dûe au compactage du sol et étaient environ 30 % plus élevées pour les sols compactés que pour les sols non compactés. Les vitesses de l'onde P ont été bien prédites en utilisant la zone de contact entre les agrégats comme principale caractéristique pour identifier les structures du sol. Le modèle a inféré des zones de contact entre les agrégats qui sont 2,9 fois plus grandes pour les sols compactés que pour les sols non compactés, ce qui indique que les sols ne se sont pas rétabli suite au compactage. Nous avons collecté les données de résistivité au cours du printemps et de l'été 2018. Afin d'interpréter ces données, nous avons développé une approche de modélisation qui combine un nouveau modèle pédophysique de propriétés électriques du sol avec un modèle unidimensionnel d'écoulement d'eau et de transfert de chaleur. Cette approche comprend un modèle d'évaporation spécifique à la structure du sol. Les données brutes de résistivité ont révélé que le compactage du sol entraîne une diminution persistante de la résistivité électrique du sol (~15 %). Ces différences sont bien reproduites par notre modèle pédophysique en invoquant une réduction de la macroporosité et de sa connectivité par le compactage. Les données de réflectométrie temporelle (TDR) et de résistivité ont révélé que les sols compactés (sol nu et sol herbeux) sont généralement plus secs (i.e., ils présentent des pertes d'eau plus importantes) que les sols non compactés. Pour expliquer cela, nous invoquons des différences de propriétés d'évaporation pour reproduire qualitativement les différences de stockage de l'eau entre les sols compactés et non compactés. Ce travail de recherche est une première étape dans l’utilisation des méthodes géophysiques pour relever le défi de longue date qu’est la quantification de la structure du sol, pour pouvoir apporter des informations pour la recherche en agronomie, diagnostiquer la dégradation chronique du sol (compactage) et aider à calibrer les modèles de surface terrestre (Land Surface Model, LSM) qui reposent sur des informations incomplètes. La thèse fournit également un plan pour l'intégration future de la géophysique et de la recherche pédologique grâce au suivi des données combiné à la modélisation.

International audience; Surface mining or other disturbing operations on ultramafic outcrops degrade soil conditions and decrease major ecosystem functions in those habitats. Human disturbances exacerbate the harsh conditions of some ultramafic soils, making recovery more difficult. Recovery of ecosystem functions of disturbed areas may vary from passive to active reclamation measures, depending on the starting situation, available resources and expected outcomes. In this study, three treatments (topsoil application, topsoil + non-compacted, and topsoil + non-compacted + organic amendment), representing a gradient of increasing reclamation effort, were tested for the reclamation of a tropical ultramafic Spolic Technosol in Sabah (Malaysia). Soil treatments were tested at the mesocosm-scale for 12 months, and drainage water fluxes, evolution of soil physicochemical parameters, soil microbial activities and spontaneous plant colonisation, diversity and growth were monitored along the duration of the experiment. The results show that application of topsoil improved the plant biomass and water filtration functions in the non-reclaimed sites, with no additional benefit from lesser compaction. The most intensive treatment (topsoil + non-compacted + organic amendment) gave the best improvements in nutrient cycling and biomass production functions, but with a reduction of water filtration function, due to an increase in soluble concentrations and cumulative fluxes of nickel. Introduced species were dominant in the vegetation colonising the mesocosms, and therefore planting of selected native species will be necessary to create habitats for native biodiversity. This information will be useful to select a strategy for the recovery of degraded tropical serpentinite quarries and dump sites.

Le developpement de l'agriculture sur les iles Loyaute (Nouvelle-Caledonie) conduit a l'utilisation plus intensive de materiel agricole qui est susceptible de modifier les caracteristiques physiques et structurales des sols et d'avoir une incidence sur l'enracinement des cultures. Quatre situations ont ete etudiees : une jachere, une graminee perenne, deux cultures de mais, l'une soumise a un travail classique, l'autre a un travail minimum. Dans chaque cas, une description morphologique, des mesures penetrometriques et des comptages racinaires ont ete realises sur un profil de sol. Les caracterisations des profils culturaux realises dans ces differentes conditions culturales montrent : une modification importante de l'etat structural, notamment dans l'horizon de surface, a la suite de la mise en culture, que le type de travail du sol n'a toutefois pas eu une incidence majeure sur la compacite du sol et l'enracinement des plantes cultivees, et que la diminution de la densite racinaire avec la profondeur ne semble pas liee a l'existence d'horizons compacts ou de zones compactees par le travail du sol. Toutefois, l'effet negatif du travail "leger" sur la croissance du mais reste a expliquer. (Resume d'auteur)

Soil compaction due to traffic is the process whereby soil bulk density is increased. The compaction level depends on the weight of the vehicle, and the soil susceptibility to compaction, which is characterized by its mechanical properties (that is, the stress-strain relationships). The plate penetrometer can be used to quantify the levels of soil compaction in-situ and supply a larger number of information on the control of this phenomenon, in real time. This paper evaluates the use of this tool with data filtering system assistance on semi confined compression assay, for predicting soil compaction in-situ, through parameters pre-compaction stress (spc) and soil compression Index (Cc). The tests were carried out on Experimental Agricultural Engineering Nucleus (NEEA in Portuguese) at West Parana State University - UNIOESTE - Brazil. The sample collection was carried at points along the tire track, 24 h after soil compaction induced by the rear tractor wheel with one, five and ten passages, on the same track. The information system is able to read all data derived from the compression test and carry out a filtering on the data by means of pre-selected parameters, plotting the compression curves and regression equations. The analysis, carried out “in situ”, avoids laboratorial procedures and gives the farmer more agility in the decision process on the management of the agricultural machinery system. Key words: Semi-confined compression test, information system, soil compaction in-situ.

Conservation agriculture (CA) is currently promoted in sub-humid and semi-arid areas of sub-Saharan Africa as a means to increase crop water use efficiency and stabilize yields. In this study, conducted during three consecutive seasons in a semi-arid area of Zimbabwe, the short-term performance of CA and current farming practices (CP) were compared in two multi-locational experiments: (1) unfertilised on-farm trials with a cotton-sorghum rotation during three consecutive seasons, and (2) farmers’ cotton fields receiving fertiliser provided on credit by cotton companies during two consecutive seasons. In both cases, residues for mulch were produced in situ . In addition to biophysical measurements, farmers’ perceptions of the technology were appraised. CA did not affect cotton productivity during the first 2 years of the experiments, which received average or above average rainfall. During the drier 2009–2010 season CA had a negative effect on crop yield both in the on-farm trials (average yield of 730 and 820 kg ha −1 under CA and CP, respectively) and in the farmers’ cotton fields (average yield of 1220 and 1440 kg ha −1 under CA and CP, respectively). There was no difference in water runoff between CA and CP on a relatively fine-textured soil, but significantly more runoff with CA on a coarser-textured soil (14 mm during the wetter 2008–2009 season), due to soil surface crusting and soil compaction. Most soils in the study area fall into this latter category. For this reason, farmers perceived ploughing as necessary during drier years to maximize water infiltration, but perceived CA as beneficial during wetter years as a means to ‘shed water’ and avoid water-logging. This is rather counterintuitive vis-a-vis the common description of CA as a water-harvesting technology. Soil crusting and compaction may be avoided by the production and retention of quantities of biomass greater than what was realised in this study (on average, only 770 kg ha −1 of residues were retained as mulch in the on-farm trials). This may be achieved through better crop management (e.g. adequate fertilisation, timely planting, crop protection) in combination with intercropping. Increasing crop primary productivity (e.g. through adequate fertilisation, timely planting and crop protection) is a pre-requisite for the principles of CA to benefit smallholders under semi-arid conditions. Our results indicate that certain legume intercropping combinations may contribute to such an end.

International audience; Increasingly mechanized timber harvesting and the repeated use of skid trail networks may affect ground vegetation differently at subsequent stages in the forest rotation. At a fine scale, no studies have yet compared the influence of micro-environmental factors and the effects of skid trail disturbance on ground flora diversity. We investigated understory diversity patterns on skid trails in 30-, 50- and 63-year-old oak forests in the northern half of France. Subplots were placed on skid trail center, wheel track, skid trail edge plus an off-trail control. At each subplot, we measured soil moisture, soil compaction (penetration resistance and bulk density) and photosynthetic active radiation and recorded the abundance of all vascular plants. The richness and abundance of ground flora were calculated based on the classification of their life form, seed bank persistence, light preference and moisture requirements. For each ecological group, we found out its best diversity indicator from subplot location, micro-environmental factors (soil moisture and compaction, light) and stand attributes (stand type, basal area), then assessed the magnitude and negligibility of the effect of the best indicator. (1) Higher soil compaction compared to controls was detected on the tracks of skid trails in the 50- and 63-year-old stands. Neither soil moisture nor light varied with subplot location whatever the stand type. (2) The best diversity indicator that showed non-negligible effects included subplot location, and soil moisture or soil compaction. Compared to controls, skid trails in the 50- and 63-year-old stands were richer in tree and short-term seed bank species, while skid trails in the 30-year-old plots had no effect on ground flora. The abundance of tree and shade-tolerant species was also higher on skid trails. Soil moisture was positively correlated with the richness of low- and high-humidity species, shade-tolerant species and transient seed bank species as well as with the abundance of short-term seed bank species. Bulk density positively affected heliophilous species richness, while penetration resistance was positively related to shrub abundance. Skid trails and soil compaction in our research area had either no impact or a positive impact on ground flora diversity. Longer-term studies of skid trail effects are needed to validate these main findings.

International audience; Forest soils host methanotrophic bacterial communities that make them a major methane sink worldwide. Soil compaction resulting from mechanization of forest operations is first affecting soil macroporosity, and thus gas and water transfer within the soil, leading to a reduced oxygenation of the soil. This reduction of soil aeration is expected to reduce the methanotrophic activity leading thus to less CH4 oxidation and more CH4 production, affecting the overall soil CH4budget. Compaction was applied in 2007 and had created linear ruts. We measured continuously since September 2014, in three different situations (compacted-mound, compacted hollow and control), soil CO2 and CH4 effluxes using closed chamber coupled to a cavity ring down spectrometer in an young oak plantation. Since December 2015, in addition to these measurements, we have implanted hydrophobic tubes to measure vertical soil profiles of CH4, O2 and CO2 concentrations in the 3 situations. The soil acts as CH4 sink, with no significant difference in net CH4uptake between control and both hollow and mound in the compacted treatment. However, the uptake of CH4 was significantly lower for the hollows than for the mounds resulting from both a lower diffusion of CH4 within soil and a higher production of CH4 in deeper layer when the soil is water saturated.

International audience; This study concludes that, from the soil compaction point of view, using tracks does not confer an advantage, because of irregular contact pressure induced by the roller presence and the overall higher load of the track system. Conversely, tyres distribute uniformly the load on all the contact area and induce overall less stress on the soil.

In perennial crops such as grapevine, there is a considerable risk of soil degradation caused by mechanization. Organic farming may increase traffic and result in more intensive soil structure degradation, especially on wet soil. Soil structure was observed in 69 soil profiles from 12 vineyards (Languedoc-Roussillon, Bordeaux, Provence, Burgundy, Rhone Valley) to study the relationships between permanent soil characteristics (texture, stoniness, waterlogging), cultivation practices (technical operations, traffic, farm equipment) and soil structure. Compaction zones were identified in soil profiles viewed perpendicularly to the grapevine rows. The percentage of compacted area and a score for compaction intensity were assessed in the top 0.5 m of the soil profile in three soil compartments defined by the distance from the grapevine row: (1) 0 to 0.2 m (2) 0.2 m to 0.5 m and (3) 0.5 m to the middle of the inter-row. Most soil profiles exhibited considerable compaction: 75% of the soil profiles were compacted in compartments 2 or 3. Intensity correlated with depth of compaction in compartment 2 – the deeper the compaction, the greater the compaction intensity. Four types of soil profiles could be identified, depending on the location of compacted zones and of their intensity of compaction. The factors that determined the types of soil profiles were as follows: soil vulnerability to compaction, use of moderating practices (practices that limit the risk of compaction) and traffic geometry. A statistical analysis resulted in a decision tree that provides a useful basis to choose cultivation practices that limit damage to or improve soil structure.

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This work was conducted in the framework of the DIGISOIL project, that is financed by the European Commission under the 7th Framework Programme for Research and Technological Development, Area “Environment”, Activity 6.3 “Environmental Technologies”.; International audience; The soil structure -i.e the spatial organisation of soil particles- changes in time and space at the decimetric scale under natural and anthropic pressures (climate, biological activity, tillage, compaction). Usual methods for characterising soil structure are destructive and time-consuming preventing spatial and temporal monitoring. New technological tools are then required. The Electrical Resistivity Tomography method (ERT), which is non-destructive and provides exhaustive description of the soil, has already been demonstrated to be useful for the description of the soil structure. However, the soil electrical resistivity is a physical parameter which depends not only on the soil structure but also on other soil characteristics, including soil water content. Changes in soil structure result in alterations of the soil water system and vice-versa by retroactions. These combined effects of soil properties on resistivity can restrict the interpretation of ERT in term of soil structure variability. The objective of this study was to characterise the spatial and temporal variability of the soil structure by the ERT method from the analysis of soil water-structure interactions on resistivity measurements. 2D ERT time monitoring has been performed for one year, in field on a small plot located in Beauce region (France). The soil was locally compacted by in-field wheel traffic to create structural zones with different bulk densities: compacted zones vs porous zones. The studied area covered both a cultivated zone and a bare soil zone to study different dynamics of water content. ERT consisted in Wenner array which gathered 72 electrodes spaced 0.1m apart. The volumic water content was monitored by TDR probes installed at several depths along the soil profile and in the different soil structural units (compacted and porous). The spatial and temporal variability of the soil structure in the first layer was analysed by i) vertical visual morphological profiles realised at six dates during the electrical resistivity monitoring, and ii) measurements of the bulk density on undisturbed soil cores sampled on the morphological profiles. After a 2D inverse modelling, resistivities were corrected from temperature effect. The analysis of ERT combined with bulk densities and morphological profiles showed relevant structural changes, especially in summer and winter. The porous zones were mainly affected by these changes in accordance with soil moisture variability in space and time. The electrical resistivity allowed to discriminate compacted zones which were less resistant than porous zones and to identify temporal changes in porous zones, especially the formation of cracks during summer. The compacted zones did not significantly evolve during the year, showing the slow resilience of the soil structure after compaction. Nevertheless, the electrical resistivity measurements demonstrated that cracking developed specifically at the contact between compacted clods and porous zones. As a consequence, the electrical resistivity increased in these cracking areas during the drying season due to their higher air content and decreased at the same locations due to preferential infiltration of water in the cracks. The 2D ERT allowed then us to describe the interactions between soil water content and structure.

Nitrous oxide (N2O) emissions comprise the major share of agriculture's contribution to greenhouse gases; however, our understanding of what is actually happening in the field remains incomplete, especially concerning the multiple interactions between agricultural practices and N2O emissions. Soil compaction induces major changes in the soil structure and the key variables controlling N2O emissions. Our objective was to analyse the ability of a process-based model (Nitrous Oxide Emissions (NOE)) to simulate the impact of soil compaction on N2O emission kinetics obtained from field experiments. We used automatic chambers to continuously monitor N2O and CO2 emissions on uncompacted and compacted areas in sugar beet fields during 2 years. Soil compaction led to smaller CO2 emissions and larger N2O emissions by inducing anoxic conditions favourable for denitrification. Cumulative N2O emissions during the crop cycles were 944 and 977 g N ha?1 in uncompacted plots and 1448 and 1382 g N ha?1 in compacted plots in 2007 and 2008, respectively. The NOE model (H´enault et al., 2005) simulated 106 and 138 g N2O-N ha?1 in uncompacted plots and 1550 and 650 g N2O-N ha?1 in compacted plots in 2007 and 2008, respectively, markedly under-estimating the nitrification rates and associated N2O emissions. We modified the model on the basis of published results in order to better simulate nitrification and account for varying N2O fractions of total end-products in response to varying soil water and nitrate contents. The modified model (NOE2) better predicted nitrification rates and N2O emissions following fertilizer addition. Using a fine vertical separation of soil layers of configurable, but constant, thickness (1 cm) also improved the simulations. NOE2 predicted 428 and 416 g N-N2O ha?1 in uncompacted plots and 1559 and 1032 g N- N2O ha?1 in compacted plots in 2007 and 2008, respectively. These results show that a simple process-based model can be used to predict successfully the post-fertilizer addition kinetics of N2O emissions and the impact of soil compaction on these emissions. However, large emissions later on during the cropping cycle were not captured by the model, emphasizing the need for further research. (Resume d'auteur)

Introduction Soil structure i. e. the arrangement of soil particles in space (Guérif, 1987) is one important factor of physic quality of soils. In the agricultural context, this structure is modified at several space and time scales by different constraints or processes: tillage, compaction by traffic, natural effects. We need methods to characterize its in situ state. They already exist but they are destructive and time consuming. Recent works (Besson et al., 2004) have shown that a compacte...

L'intensification de la récolte de biomasse forestière a des impacts sur la biodiversité des écosystèmes forestiers, sur la physico-chimie des sols et des ressources en eau. Ce chapitre présente les préconisations en l'état des connaissances actuelles pour limiter ces impacts, lors des opérations de récolte du bois, pour la conduite des peuplements (régénération, choix des essences, âges d'exploitabilité) et dans le cas particulier des cultures dédiées (TTCR). / The increase in forest biomass harvesting has an impact on forest biodiversity and natural resources (soils, water). In ordre to limit these impacts, this chapter gives guidelines concerning biomass harvesting, forest stand management (regeneration, objective species, rotation age) as also the particular case of short rotation coppices.

Embora associada à adoção de tecnologias de conservação do solo, a intensificação dos sistemas de produção agropecuária tem induzido a um dos principais problemas enfrentados pelos agricultores, a compactação do solo, seja em sistemas de plantio direto ou em sistemas de plantio convencional e pastagem. Este estudo foi realizado em Rio Verde, GO, em Latossolo Vermelho Amarelo, nos seguintes sistemas: plantio direto há 14 anos (SD14); plantio direto há oito anos (SD8); plantio direto há dois anos (SD2); preparo convencional (PC); pastagem (P) e floresta (F). A resistência à penetração do solo foi determinada utilizando-se o penetrômetro de Impacto Modelo IAA/Planalsucar - Stolf, a partir da superfície do solo até a profundidade de 0,40 m; determinaram-se, também, a densidade do solo e a granulometria. O plantio convencional apresentou menor resistência à penetração, na profundidade 0-0,10 m, enquanto o SD2 indicou maior resistência à penetração até 0,40 m de profundidade. Abaixo da profundidade de 0,15 m não houve diferença significativa entre os tratamentos PC, SD8, SD14. Os dois primeiros anos de adoção do sistema de plantio direto são críticos quanto à resistência a penetração nas camadas superficiais do solo. The intensification of agricultural production systems has caused soil compaction even when soil conservation technologies are adopted. Soil compaction is one of the main problems for farmers, both in no-tillage and in conventional-tillage systems, as well as in pasture. This study was conducted in Rio Verde, (State of Goias), on Red-Yellow Latosol under the following systems: no-tillage for 14 years (SD14); no-tillage for 8 years (SD8); no-tillage for 2 years (SD2); conventional tillage (CT); pasture (P) and forest (F). The soil resistance to penetration was measured by the impact penetrometer Model IAA/Planalsucar - Stolf, from soil surface to the soil depth of 0.40 m. Soil bulk density and granulometry were also determined. Conventional tillage had lower resistance to penetration at the 0-0.10 m depth, whereas SD2 had more resistance up to 0.40 m in depth. There were no significant differences below 0.15 m in depth among treatments CT, SD8, and SD14. The first two years under the no-tillage system are critical, with regard to the resistance to penetration in to the soil surface layers.

E-mail Address: ralisch@uel.br; mfatima@uel.br; graziela_barbosa@iapar.br; eric.scopel@cirad.fr; luizcarlos.balbino@embrapa.br; International audience; The intensification of agricultural production systems has caused soil compaction even when soil conservation technologies are adopted. Soil compaction is one of the main problems for farmers, both in no-tillage and in conventional-tillage systems, as well as in pasture. This study was conducted in Rio Verde, (State of Goias), on Red-Yellow Latosol under the following systems: no-tillage for 14 years (SD14); no-tillage for 8 years (SD8); no-tillage for 2 years (SD2); conventional tillage (CT); pasture (P) and forest (F). The soil resistance to penetration was measured by the impact penetrometer Model IAA/Planalsucar – Stolf, from soil surface to the soil depth of 0.40 m. Soil bulk density and granulometry were also determined. Conventional tillage had lower resistance to penetration at the 0-0.10 m depth, whereas SD2 had more resistance up to 0.40 m in depth. There were no significant differences below 0.15 m in depth among treatments CT, SD8, and SD14. The first two years under the no-tillage system are critical, with regard to the resistance to penetration in to the soil surface layers; Embora associada à adoção de tecnologias de conservação do solo, a intensificação dos sistemas de produção agropecuária tem induzido a um dos principais problemas enfrentados pelos agricultores, a compactação do solo, seja em sistemas de plantio direto ou em sistemas de plantio convencional e pastagem. Este estudo foi realizado em Rio Verde, GO, em Latossolo Vermelho Amarelo, nos seguintes sistemas: plantio direto há 14 anos (SD14); plantio direto há oito anos (SD8); plantio direto há dois anos (SD2); preparo convencional (PC); pastagem (P) e floresta (F). A resistência à penetração do solo foi determinada utilizando-se o penetrômetro de Impacto Modelo IAA/Planalsucar – Stolf, a partir da superfície do solo até a profundidade de 0,40 m; determinaram-se, também, a densidade do solo e a granulometria. O plantio convencional apresentou menor resistência à penetração, na profundidade 0-0,10 m, enquanto o SD2 indicou maior resistência à penetração até 0,40 m de profundidade. Abaixo da profundidade de 0,15 m não houve diferença significativa entre os tratamentos PC, SD8, SD14. Os dois primeiros anos de adoção do sistema de plantio direto são críticos quanto à resistência a penetração nas camadas superficiais do solo

Soil compaction is often studied by comparing virgin sites to commercial fields with a long-term cultivation history. The establishment of a new research farm in a virgin area of the Mpumalanga province in South Africa provided an opportunity to induce compaction to quantify the buffer capacity of a virgin soil against degradation of its soil physical properties. The soil of the trial site is a shallow (±0.4 m) Cambisol with uniform texture (±44% clay), and 3.8% organic matter in the A-horizon, overlying weathered basalt. Row spacings were 1.5 m and 1.8 m, and only haulage vehicles with matching wheel spacings were allowed in the field. Compaction treatments, starting after harvest of the plant crop in 2003, consisted of pressure applied with commercial 30 ton capacity loaded haulage vehicles fitted with either radial tyres or high flotation tyres. After harvest the soil was kept dry in one part of the field and watered elsewhere to create differential water contents at the time of treatment application. Results showed reduced water infiltration rates, increased soil bulk density, increased penetration resistance and reduced root distribution in all the compaction treatments. The treatments with a higher water content were more susceptible to degradation. It is concluded that even a virgin soil in good physical condition will be degraded over the period of a few years to the physical threshold limits. The buffer capacity of this soil against compaction (and therefore of most other soils) degraded over a period of only three years. Permanent traffic lanes should therefore be considered essential in most agricultural systems to protect the productive areas of fields. Proper spacing of interrows and the use of low pressure high flotation tyres on all axles should be considered as additional measures to achieve this goal.

Characterisation of soit structure within the tilled layer of cultivated fields is crucial because the importance of this soil characteristic on the biological, chemical and physical properties of the soil and its repercussions on water cycle, root growth and functioning. We present in this paper a method for field characterisation of soil structure. This method, practised since the 1970s, was designed for field diagnosis of the effects of cropping systems on soil structure. It is based on a stratification of the observation face of a pit dug perpendicular to the direction of tillage and traffic: spatial compartments are distinguished, according to the nature of the mechanical stresses they have been submitted to during tillage and crop management. Characterisation of soil structure is performed on a morphological basis, using two criteria, each of them addressing a specific organisation level of the soil: firstly, clods size distribution, proportion of fine soil and the way the clods are brought together are considered; then, secondly, the clods are classified in three types, on the basis of the importance and the origin of their internal structural porosity. Physical measurements (bulk density, compaction test, and water retention) are presented, which demonstrate that physical behaviour is different between clod types. These results justify the use of the method to model changes with time in soil structure, under the effects of the main factors affecting soil structure dynamics in tilled fields: compaction, fragmentation, climate and biological activity. A model which simulates at the field scale the changes overtime of the proportion of compacted clods within the tilled layer is presented. In this model, the tilled layer is represented as a set of 1 cm2 pixels, regularly located on a square grid. Each pixel is defined by its co-ordinates and a specific structure, compacted or non compacted. The pixel co-ordinates are modified during ploughing, for which the model calculates the lateral and vertical displacement of the soil. The structure of any individual pixel can be changed, depending on the soil condition and the operation type. This model was evaluated by comparing its outcomes to measurements obtained from a long term field experiment designed to study soil structure dynamics. (Resume d'auteur)

La culture de la canne à sucre est introduite dans le système de culture des producteurs de bananes de la région de Capesterre afin de réduire l'utilisation polluante et onéreuse des pesticides. Ce travail présente l'étude de l'effet des racines de cannes à sucre sur la structure dégradée des sols de cette région. Nous avons réalisé des observations macroscopiques de l'état du profil cultural dans des situations caractéristiques de culture de cannes et de bananiers et caractérisé "in situ" la géométrie des systèmes racinaires correspondants. Nous avons démontré qu'il existe une relation étroite entre le travail des racines de canne et la restructuration des sols. La canne à sucre représente un moyen d'améliorer la structure des sols à condition de modifier les itinéraires techniques actuels.

Les problèmes d'érosion au Brésil ont conduit les agriculteurs à adopter, au cours des vingt dernières années, des techniques de cultures moins agressives. Le semis direct constitue, à ce titre, une alternative intéressante en termes de faisabilité et de durabilité. Pour étudier l'influence de cette technique de culture à long terme, le CIRAD mène, depuis 1998, un projet de caractérisation et de modélisation grace a des parcelles expérimentales et à des analyses chez des agriculteurs, en partenariat avec le CNPAF de Goiânia (Etat du Góias, Brésil). Ce rapport présente les premiers résultats en milieu réel. A partir d'observations, de mesures et de prélèvements de sol non remanié, sur un ensemble de parcelles au passé différencié (semis directs ayant subi des labours aux disques à des dates différentes, technique conventionnelle de labour aux disques lourds tractés), nous avons tenté de dégager des pistes de recherche et de définir la pertinence de certains outils pour la caractérisation des propriétés physiques, chimiques et biologiques du sol. Cette étude a mis en évidence des différences de densité apparente entre les traitements, avec une compacité inférieure sous "labour", même en profondeur et une modification à long terme, sous semis direct, du spectre poral. Cependant, de nombreuses mesures ne montrent pas de différences significatives en faveur d'un traitement (infiltration, rétention en eau). Les bonnes qualités physiques et chimiques de ce type de sol (sol ferralitique sur basalte) n'ont, sans doute, pas permis d'exprimer les effets attendus du semis direct.

For coarse-textured soils of high subsoil permeability, research has demonstrated the benefits of subsoil compaction for improved water and nutrient-use efficiency in rainfed lowland rice (Oryza sativa L.). To better define soil conditions suited to this subsoil compaction, on-farm experiments were carried out on soils varying in subsoil clay content. In 1993 and 1994 rice (cv. KDML105) was grown in main plots comparing shallow dry tillage without compaction, shallow dry tillage with subsoil compaction, and deep dry tillage with subsoil compaction. Soil was compacted in seven farmers' fields in the south of Ubon Ratchathani Province, with 10 passes of a vibrating road roller on 19 and 23 May 1993. The effects of subsoil compaction on changes in soil physical and hydrological properties differed according to subsoil clay content, which ranged from 1.4% to 12.0%. Subsoil compaction decreased soil hydraulic conductivity sufficiently for fields with subsoil clay content greater than 2%. When subsoil clay content was higher than 10%, the justification for using relatively costly subsoil compaction was questionable, as the hydraulic conductiviy was already low and the gains in water-storing capacity seemed limited. Based on these results, proportions of soils with subsoils of 10% day were mapped using geographic information systems for an area of about 40,000 ha within the Ubon Ratchathani Land Reform Area. About 40% of the mapped area had subsoils with clay % between 2 and 10, suggesting that substantial areas could be suitable for subsoil compaction. More investigations are needed to assess its economic and social acceptability, to better understand variability and probability of response, and to further refine soil suitability in relation to clay type, clay content and groundwater changes at the toposequence level.

The study was carried out in a high yielding field (HYF) and a lower yielding field (LYF). Soil samples were collected in an increment of 15 cm down to 75 cm during the growing season (moist) and after harvest (dry) and from a virgin site. The bulk densities (BD) of LYF under the ridge are higher than those of HYF whereas the BD under the furrow in HYF are higher than those of the LYF The study shows that under dry soil conditions the BD values under the ridge are lower than those of the virgin land in the top 30 cm whereas below 30 em the BD of the cultivated land are higher than those of the virgin land. Under moist soil conditions and below 15 cm, BD under the ridge of cultivated land are lower than those of the virgin land. Under furrow BD of cultivated land are lower than those of the virgin land. Available water capacity of the cultivated land is about 12% while that of the virgin land is 19%. Soil moisture curves show some variability in water retention of these two fields while in virgin land the curves cluster around a narrow range for any pF level reflecting uniformity of pore size.

Erosion et environnement sont des sujets sensibles aux Antilles. Les rivières torrentielles qui dévalent les montagnes volcaniques provoquent des crues spectaculaires et leurs eaux brunâtres traversent les plantations, envasent les anses maritimes et polluent les côtes touristiques. Cependant, quand on parcourt les bananeraies qui couvrent les mornes de Martinique, les indices d'érosion ne sont pas nombreux : on observe des zones de tassement de la surface du sol, quelques rigoles sur les pentes de plus de 20%, de profondes ravines qui drainent les flancs des collines, mais aucune croûte de battance. Localement, le long des routes et des torrents, on apperçoit des glissements de terrain sur des pentes très raides (supérieures à 50%). Sur les terres travaillées fréquemment, on peut observer des talus (hauteur dépassant un mètre en une dizaine d'années), conséquences de l'érosion mécanique sèche provoquée par les outils de travail du sol. Les pluies se répartissent de façon très hétérogène sous bananeraie ; on a observé une zone de concentration des eaux le long des faux troncs et sur le glacis dénudé autour des souches (où sont concentrés les engrais et les nématicides), puis une zone protégée par la canopée en forme de parapluie et enfin, une zone pilonnée par de grosses gouttes qui se concentrent au bout des feuilles, découpent des agrégats et creusent de petites dépressions. Au-delà de 15% de pente, on observe quelques griffes d'érosion qui concentrent les eaux de ruissellement dans l'interrang, mais les vieilles feuilles et autres résidus de culture ralentissent les eaux de surface et limitent très efficacement l'érosion linéaire. L'étude (par la méthode des points quadrats) des états de surface du sol sous bananeraie établie a montré que la canopée couvre 64% de la surface, les souches et les glacis peu perméables occupent 18%... (D'après résumé d'auteur)

Two-factor field experiments during 1993 and 1994 with sharply contrasting wet seasons were carried out for in situ water conservation and nutrient use in rainfed lowland rice (Oryza sativa L.) grown on a sandy soil. The main plots compared subsoil compaction with shallow dry tillage (C1), subsoil compaction with deep dry tillage (C2), and shallow dry tillage without compaction (C0). Five mineral fertilization techniques were used as subplot treatments: no fertilizer (control, F0), 40-13-25 kg NPK/ha in two applications of conventional fertilizer (F1), 40-13-25 kg NPK/ha using slow-release fertilizer (F2), 80-26-50 kg NPK/ha in two applications of conventional fertilizer (F3), and 80-26-50 kg NPK/ha using slow-release fertilizer (F4). Soil was compacted with 10 passes of a vibrating road roller on 15 May 1993. Rice seedlings (cv. RD6) were transplanted in all plots. Compaction increased total weeks with surface water accumulation from 3.7 and 2.4 wk in C0 to 11.0 and 14.3 wk in C1, and 11.7 and 14.9 wk in C2 for the 1993 and 1994 wet seasons, respectively. Because three irrigations were applied during the 1993 WS, drought stress was far more severe during the nonirrigated 1994 WS. With the single exception of the effect on rice grain weight in the 1994 WS, no significant interaction between the main factors (compaction) and subfactors (fertilization) was observed. Although the highest grain production was also harvested in compacted plots in the 1993 WS, grain yield increase because of subsoil compaction was found to be significant (P

Un modèle d'évolution d'un indicateur de l'effet à long terme des systèmes de culture sur l'état structural de parcelles labourées est présenté. La méthode de description morphologique du profil cultural proposée par Manichon (1982) est utilisée, avec un niveau de description de l'état structural, l'état interne des éléments structuraux, comprenant trois modalités entre lesquelles il existe des termes de passage à travers les effets de compactage et de fragmentation liés à la pratique du système de culture. L'une de ces modalités, appelée D, représente un état de compacité limite des mottes, résultant de compactages sévères en conditions humides. Nous proposons de simuler l'évolution de la proportion d'éléments d'état interne D, indicateur du solde du bilan entre compactages et décompactages subis par le profil. La méthode de simulation proposée repose sur une représentation de la couche labourée par une matrice de points répartis sur une maille carrée de deux cm, chaque point étant défini par ses coordonnées et un état interne D ou non D. Un programme informatique évalue, à chaque intervention culturale le devenir de chacun de ces points : déplacement sans changement d'état lors du labour, forçage à l'état non D dans l'horizon de surface pour simuler l'action de fragmentation intense des outils de reprise et du climat dans l'horizon superficiel et forçage à l'état interne D des points situées sous les passages de roues lorsque ceux-ci ont lieu en conditions humides. La modélisation proposée permet ainsi de simuler l'évolution de la répartition spatiale au sein du profil des éléments tassés et non tassés, sur plusieurs années. On a obtenu une bonne concordance entre les résultats de cette simulation et l'observation de l'état structural de deux parcelles expérimentales différant par la fréquence des tassements exercés sur le profil

Dans les conditions tropicales humides de la culture mécanisée de canne à sucre à la Réunion, la traficabilité du sol est déterminante au moment de la récolte annuelle, caractérisée par le passage d'engins lourds et par des problèmes de compaction. Les opérations de replantation sont moins fréquentes (5 à 8 ans), mais sont souvent réalisées en conditions humides. Dans un premier temps, on examine la traficabilité sous l'angle de la sensibilité au tassement. Un seuil de teneur en eau critique (38 g.cm-3) est mis en évidence par le test Proctor modifié, dont l'énergie mise en jeu correspond aux conditions de culture (140 kJ.m-3). Les performances d'un tracteur au labour sont ensuite mesurées au champ, selon différentes conditions de teneur en eau initiale dans la couche superficielle. On met en évidence ainsi une teneur en eau critique, identique à la précédente, et déterminante sur le fonctionnement de la cellule motrice (glissement, dépense énergétique). Ce seuil semble donc déterminer à la fois la traficabilité, au sens restreint de la sensibilité au tassement du sol, et l'efficience d'intervention des matériels. On note qu'il représente près de 95% de la teneur en eau à la capacité au champ, valeur souvent retenue par la littérature comme seuil de traficabilité. Dans un second temps, un modèle d'évolution climatique de la teneur en eau dans la couche superficielle (0-20 cm) est élaboré [...]

In Reunion Island and other areas where mechanised sugar cane production is practised under wet tropical conditions, soil trafficability is decisive at the time of the annual harvest and post harvest works which involve the use of heavy machines causing compaction problems. Problems relating to the planning of harvest operations are predominant. Operators are faced with two types of question : i) what is the risk involved, and what are the probable results of an operation undertaken at a given period ? How and when can problems of compaction be remedied if they arise (decompaction after harvest) ?; and complementary to this, for planning purpose, ii) which is the period, or which are the days best suited for the operation in a given area ? First, trafficability is examined from a compaction susceptibility viewpoint. A critical threshold for moisture content is evidence by way of the modified Proctor test. Then, a model for climatic evolution of moisture content on the upper layer of the soil is developed. It is calibrated and takes into account the specific characteristics of cane growing and certain decision criteria used by operators. From the moisture content threshold determined, the model can coonstitute a decision system, i) at particular moment using recent climatic data, ii) prospectively on virtual scenario and, iii) for yearly planning purpose, from frequencial analysis of occurence of trafficable days

Dans les conditions tropicales humides de la culture mécanisée de canne à sucre à la Réunion, la traficabilité du sol est déterminante au moment de la récolte annuelle, caractérisée par le passage d'engins lourds et par des problèmes de compaction. Dans un premier temps, on examine la traficabilité sous l'angle de la sensibilité au tassement. Un seuil de teneur en eau critique (38 g.cm-3) est mis en évidence par le test Proctor modifié, correspondant aux conditions de culture (140 kJ.m-3). Les performances d'un tracteur au labour sont mesurées au champ, selon différentes conditions de teneur en eau initiale dans la couche superficielle. On définit ainsi une teneur en eau critique, identique à la précédente, déterminante sur les états structuraux résultants, et sur le fonctionnement de la cellule motrice. Ce seuil semble déterminer à la fois la traficabilité, au sens restreint de la sensibilité au tassement du sol, et l'aptitude au labour, au sens de l'efficience d'intervention des matériels. Dans un second temps, un modèle d'évolution climatique de la teneur en eau dans la couche superficielle (0-20 cm) est élaboré. Il est calibré lors d'expérimentations et prend en compte des caractéristiques culturales de la canne à sucre. A partir du seuil de teneur en eau critique déterminé, le modèle peut constituer un outil d'aide à la décision en temps réel sur des données climatiques récentes, prospectif, sur des scénarios virtuels, ou pour la planification annuelle, à partir d'analyse fréquentielle de l'occurence de jours traficables.

Dans les conditions tropicales humides de la culture mécanisée de canne à sucre à la Réunion, les producteurs évoquent souvent les problèmes de traficabilité, en terme de risques agronomiques liés au tassement des sols. La traficabilité du sol est déterminante au moment de la récolte, caractérisée par de nombreux passages d'engins lourds, et par des problèmes de compaction. L'aptitude au labour intéresse les opérations moins fréquentes de replantation, mais qui sont souvent réalisées en conditions humides. Une zone d'étude a été choisie. Des expérimentations préalables ont permis, de mettre en évidence un seuil de teneur en eau critique, à la fois en terme de risque de tassement, d'évolution des structures sous travail du sol, et de performances des cellules motrices. Un modèle d'évolution climatique de la teneur en eau dans la couche superficielle est élaboré. Il est calibré lors d'expérimentations spécifiques et prend en compte des caractéristiques culturales de la canne à sucre. A partir du seuil de teneur en eau critique déterminé, le modèle peut apporter des informations (i) en temps réel sur des données climatiques récentes, (ii) à caractère prospectif, sur des scénarios virtuels, (iii) ou pour la planification annuelle, à partir d'analyse fréquentielle de l'occurence de jours traficables. Sa confrontation avec les aspects organisationnels constitue une piste intéressante

Une dégradation de la fertilité des sols dans les systèmes intensifs de monoculture bananière est observée actuellement aux Antilles françaises. Cette dégradation provient de replantations fréquentes et de la mécanisation de nombreuses opérations culturales. Pour un travail du sol de qualité en bananeraie industrielle, la rotobêche est préconisée par le CIRAD. Cet outil évite les tassements, lissages et compactage et la formation de semelle de labour; il permet une préparation du sol correcte y compris en sols collants; il est utilisable en destruction de bananeraie et il présente un effort de traction limité. Quatre schémas comparatifs montrent un profil cultural après passage de disques lourds, après sous-solage suivi d'un sillonnage classique, après labour, et enfin, après passage de la rotobêche

Cette mission, suscitée et financée par le MSIRI, avait pour objet d'apporter un appui technique opérationnel à la Division "Mécanisation" et à l'activité "physique des sols" de la Division "Irrigation", - concernant les expérimentations en cours ou à mettre en place en matière de préparation des sols, ainsi que sur des problèmes de métrologie embarquée, - concernant le programme de travail d'un chercheur rattaché à la Division "Irrigation" mais qui développe des actions en matière d'étude et gestion physique des sols, en collaboration avec la Division "Mécanisation", notamment sur la compaction des sols sous canne mécanisée. Le présent rapport s'articule en deux parties. Il s'attache tout d'abord à identifier et à reformuler les problèmatiques telles qu'elles ont été présentées par les chercheurs rencontrés. Viennent ensuite des observations relatives aux dispositifs, aux méthodes appliquées, ainsi que des propositions d'ordre technique, organisationnel, notamment en regard des expérimentations prévues

Nous étudions expérimentalement les interactions sol/machine dans la réalisation de labours en conditions réelles sur des sols ferrallitiques sous couvert de canne à sucre. Différentes conditions initiales du sol ont été choisies : humidité de la couche superficielle du sol variable, hétérogénéité parcellaire due au système de culture canne. La caractérisation des conditions initiales et résultantes du milieu nous permet d'apprécier l'impact des pratiques culturales sur ce type de sol. La métrologie embarquée nous renseigne sur le comportement du matériel lors de la réalisation du labour. La mise en oeuvre de cette technique précise les modalités de la méthodologie qui lui est associée. Le système de culture de la canne à sucre étudié génère une hétérogénéité parcellaire en ce qui concerne la répartition de la fertilité du sol. Les capteurs associés à la cellule motrice rendent bien compte de son fonctionnement et possèdent une bonne fiabilité. Ceux associés à l'outil donnent des résultats avec une grande variabilité rendant difficile la mise au point de modèles déterministes. Les conditions initiales du sol ont un impact direct sur le fonctionnement du matériel. Le labour ne corrige pas l'hétérogénéité de répartition de la fertilité sur la parcelle

La compacité du sol a des répercussions sur le développement du bananier au champ. Elle provoque une diminution de la taille du plant et de son régime, un retard de floraison et une réduction du nombre de rejets émis. Des facteurs autres que la compacité du sol sont susceptibles d'agir sur le développement des racines (parasitisme tellurique, drainage). Dans l'expérimentation effectuée sur des andosols en Guadeloupe, le compactage du sol s'est surtout traduit par une réduction de l'aération du sol et il a produit des asphyxies racinaires, mais il a eu aussi d'autres effets sur l'enracinement : diminution du nombre de racines, augmentation de leur diamètre et accroissement sensible de la masse racinaire. La compacité du sol entraîne également des perturbations de la nutrition du bananier : réduction de l'absorption de N, P, K et Ca, absorption massive de Mn.