Soil structure

Summary

In geotechnical engineering, soil structure describes the arrangement of the solid parts of the soil and of the pore space located between them. It is determined by how individual soil granules clump, bind together, and aggregate, resulting in the arrangement of soil pores between them. Soil has a major influence on water and air movement, biological activity, root growth and seedling emergence. There are several different types of soil structure. It is inherently a dynamic and complex system that is affected by different factors. Overview Soil structure describes the arrangement of the solid parts of the soil and of the pore spaces located between them (Marshall & Holmes, 1979). Aggregation is the result of the interaction of soil particles through rearrangement, flocculation and cementation. It is enhanced by: the precipitation of oxides, hydroxides, carbonates and silicates; the products of biological activity (such as biofilms, fungal hyphae an

Official source

https://en.wikipedia.org/wiki/Soil_structure

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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

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

Géraldine Michèle Bullinger, Jean-Michel Gobat, Claire Guenat, Renée-Claire Le Bayon

2007

2015