Structure (pédologie)

En pédologie, la structure est la façon selon laquelle s’arrangent naturellement et durablement les particules élémentaires du sol, en formant ou non des agrégats. L’agrégat est le résultat de l’organisation naturelle des constituants, ce en quoi il est fondamentalement différent d’un fragment, lequel résulte de la brisure d’un objet préexistant. Tous les mécanismes et processus de la pédogenèse (actions physiques, chimiques et biologiques) concourent à transformer des matériaux à structure lithologique (roche et dépôts) en matériaux à structure pédologique. Structures prédéfinies Des grands types de structures sont prédéfinies : ; Sans structure : Aucune agrégation visible ni disposition ordonnée et définie autour des lignes naturelles de faible résistance. ; Structure lithique (ou lithologique) : Absence d’agrégats, structures non pédologiques héritées de la roche-mère. ; Structure massive (ou continue) : Absence d’agrégats, horizon cohérent, pouvant être plus ou moins

Optimization of drip irrigation using a sensor network in Sahel Region (Burkina Faso) - Analysis of soil water and plant dynamics in the framework of project Info4Dourou 2.0

Tom Müller

The research project Info4Dourou 2.0 's main goal is to improve agriculture in semi-arid regions by developing a support system that optimizes agricultural production and water consumption based on continuous soil humidity measurements using a sensor network. In this context, the main purpose of the study was to give more scientific support to the agronomic model on which the sensor network is based. In particular the research aims at understanding the soil water and plant dynamics in order to give recommendations on the system design. The main feature of the system is to indicate when irrigation must be triggered and in which soil moisture conditions. The thesis developed a numerical model based on the software HYDRUS 2D to acquire a precise knowledge on the soil water dynamics and was calibrated and coupled with field experiments on two vegetable crops of eggplant and cabbage in Burkina Faso using drip kit irrigation systems. A great focus was given on the plant response to different irrigation schedules and to water stress, considering aerial biomass development, root distribution and final yields. Water stress was linked to continuous measurements of the soil matrix potential at different depth and locations. The field experiments showed that a daily irrigation frequency resulted to better canopy development during the first part of the growth but that great water savings are possible by optimizing the schedule. Water stress was difficult to track precisely by following daily sap flow behaviour which suggested that plant stress occurs before transpiration reduction, especially when biomass is building up. The adaptability of the root distribution was demonstrated and was clearly correlated with the wetted zone which depended on the irrigation schedule. From the numerical model, it was shown that using one sensor at a depth of about 10 cm was most appropriate in order to pilot irrigation during the whole crop growth. The analysis showed that most of the water savings could be achieved at relatively high threshold values and that low thresholds mainly resulted to transpiration reduction which was not advisable. A threshold of -20 kPa was proposed for the beginning of the growth stage which then decreases to a value of -50 kPa at full canopy development. These thresholds are believed to be adequate for most vegetable crops since they allow keeping the soil matrix potential in the root zone at values that are tolerated by most plants. An analysis of the influence of the soil texture also showed that similar values seem to perform well for most soils, if assuming an adaptation of the root distribution to the wetted zone. The study focused mainly on water stress but more research could be done on the impact of the irrigation system on nutrients availability for example.

2015

Coupling X-ray computed tomography and freeze-coring for the analysis of fine-grained low-cohesive soils

Claire Guenat, Renée-Claire Le Bayon, Adrien Francis Olivier Liernur, Andreas Cedric Schomburg, Pascal Turberg

This paper presents the coupling of freeze-core sampling with X-ray CT scanning for the analysis of the soil structure of fine-grained, low-cohesive soils. We used a medical scanner to image the 3D soil structure of the frozen soil cores, providing X-ray CT data at a millimetric resolution over freeze-cores that are up to 62.5 cm long and 25 cm wide. The obtained data and the changes in gray level values could be successfully used to identify and characterize different soil units with distinctly different physical properties. Traditional measurements of soil bulk density, carbon and particle size analyses were conducted within each of the identified soil units. These observations were used to develop a 3D model of soil bulk density and organic matter distribution for five freeze-cores obtained at a restored floodplain in Switzerland. The millimetric X-ray CT scanning was applied to detect the impact of freeze-coring on the soil structural integrity. This allows identifying undisturbed zones, a critical precondition for any subsequent assessment of soil structure. The proposed coupling is thought to be applicable to a wide range of other low-cohesive soil types and has a large potential for applications in hydrogeology, biology or soil science.

Elsevier Science Bv2017

Optimization of drip irrigation using a sensor network in Sahel Region (Burkina Faso) - Analysis of soil water and plant dynamics in the framework of project Info4Dourou 2.0

Tom Müller

2015

Optimization of drip irrigation using a sensor network in Sahel Region (Burkina Faso) - Analysis of soil water and plant dynamics in the framework of project Info4Dourou 2.0

Coupling X-ray computed tomography and freeze-coring for the analysis of fine-grained low-cohesive soils

Influence of some physicochemical and biological parameters on soil structure in alluvial soils

Optimization of drip irrigation using a sensor network in Sahel Region (Burkina Faso) - Analysis of soil water and plant dynamics in the framework of project Info4Dourou 2.0

Influence of some physicochemical and biological parameters on soil structure in alluvial soils

Coupling X-ray computed tomography and freeze-coring for the analysis of fine-grained low-cohesive soils