The Organization of Soil Fragments

Kubiëna (1938) was the first to introduce the concept of fabric in soil micromorphology, so this term has been used in soil micromorphology for a long time. The term “fabric” was initially applied to rocks by geologists and petrologists. This type of fabric is defined as the “factor of the texture of a crystalline rock which depends on the relative sizes, the shapes, and the arrangement of the component crystals” (Matthews and Boyer 1976). This definition has been adapted for soil micromorphology and its latest definition has been given by Bullock et al. (1985) as: “soil fabric deals with the total organization of a soil, expressed by the spatial arrangement of the soil constituents (solid, liquid, and gaseous), their shape, size, and frequency, considered from a configurational, functional and genetic view-point”. In conclusion, the soil micromorphologist should consider the fabric as an arrangement and∕or organization of soil constituents.

Observation of Soils: From the Field to the Microscope

As emphasized by W. Kubiëna, “… there exists no other method capable of revealing the nature and complexity of soil polygenesis in so much detail as thin-section micromorphology and at the same time enabling one to follow and explain its formation...”. This sentence, cited by Fedoroff (1971), highlights the aim of soil micromorphology: looking at a soil from the inside and at various scales, from the optical microscope to synchrotron imaging. Soils constitute multiscalar objects by definition, from their soilscape (at the landscape scale), to their profile and its horizons to the atomic interactions between the smallest minerals and organic molecules. Micromorphology enters the soil investigations at the multi-centimetre scale (see “File 3”) at which the thin section is made.

Pedogenic Features

From a historical point of view, soil micromorphology was first used in order to decipher the expressions of pedogenic processes at the microscale (Kubiëna 1938). In the preceding chapters, the Atlas listed a series of descriptive tools to help with the identification of objects. This chapter deals with specific pedofeatures encountered in a large diversity of soils and directly related to pedogenic processes. Pedological features (Brewer 1964) or pedofeatures (Bullock et al. 1985) are “discrete fabric units present in soil materials that are recognizable from an adjacent material by a difference in concentration in one or more components or by a difference in internal fabric” (Stoops 2003, 2021). In Stoops (2003, 2021), pedofeatures are subdivided into two categories: matrix pedofeatures and intrusive pedofeatures. Matrix pedofeatures can be subdivided according to their relationship with the groundmass (depletion, impregnative, and fabric pedofeatures) and to their morphology (hypocoatings, quasicoatings, matrix infilling, intercalation, and matrix nodules). Regarding the intrusive pedofeatures, they include coatings, infillings, crystals and crystal intergrowth, intercalations, and finally nodules. The proposed nomenclature of this chapter is based on the nature and morphology of the pedofeatures, simplified from Bullock et al. (1985).

The Future of Soil Micromorphology

The advancement of technology opens up new opportunities to soil micromorphology. Although a description using an optical microscope of the fabric and the various constituents of soils will be always necessary to investigate soil evolution, the uncovered thin section leaves soil material on which analyses can be performed. Since the 1970s, it was possible to observe thin sections at high resolution with the scanning electron microscope in its backscattered electron mode (see “10.1007/978-3-030-67806-7_1#Sec7”). It was also possible to generate chemical images with electron microprobes. But these conventional techniques, as well as new ones, greatly improve the study of matter interactions in soils, not only by enhancing the spatial resolution with incredible precision but also by providing chemical and mineralogical images, which substantially increased the accuracy of micromorphological diagnostics. By coupling morphological and chemical approaches, including stable isotope imaging in soil material, the future of soil micromorphology will undoubtedly offer new opportunities to solve specific problems, especially in the field of organomineral interactions in soils. It is wise to say that soil micromorphology, with its analytical and holistic approaches, will make it possible to build the necessary solid foundations needed for investigations that are increasingly oriented towards nanoscale objects: it will remind us that the trees should not hide the forest.