charred organic matter in Black Chernozem soils of Saskatchewan. Can. J. Soil Sci. 81: 285-297. A combination of both conventional and novel techniques, such as micromorphology, scanning electron microscopy, and high energy ultraviolet photo-oxidation, have been applied to estimate the proportion of charred organic C in Black Chernozem soils in Saskatchewan. Char was represented by products of incomplete combustion of both arboreal and herbaceous vegetation. Char was found in all particle size fractions of A horizons of Black soils. Char was represented by a variety of forms, from fresh and angular, to rounded and clay-coated particles in the silt fraction. It is likely that the surface area and ability to adsorb clay vary with the size and nature of char particles. Sand-sized char includes particles with various surface properties and adsorptive ability. Generally, younger and lighter char with hydrophobic properties appears to be in the clay-sized fractions, whereas the silt contains heavier char particles coated with clay or containing clay in pores. Ultrasound, used to disperse soils, may fracture larger particles to finer sizes. The proportion of organic C in soils and fractions that is resistant to UV-oxidation was as high as 60%, which, based on published guidelines, indicates a very substantial char component in Black soils. CPMAS 13 C NMR spectra indicate a strong aromatic peak at 130 ppm, also consistent with the presence of char. Results indicate that char particles as fine as silt size are present in significant amounts in Black soils, suggesting that char is an important component, and indicating the need for a new concept of humus formation and storage in Black soils. En combinant diverses techniques classiques et innovatrices comme la micromorphologie, la microscopie électronique à balayage et la photo-oxydation par les rayons ultraviolets à haute énergie, les auteurs ont estimé la quantité de matière organique carbonisée (C) présente dans les tchernozems noirs de la Saskatchewan. Le charbon émane de la combustion partielle de la végétation (arborée et herbacée). Il existe dans toutes les fractions de l'horizon A des sols noirs, peu importe leur granulométrie. Le charbon se présente sous diverses formes : de particules fraîches et anguleuses aux particules arrondies, enrobées d'argile, dans la fraction limoneuse. La surface active et la capacité d'adsorber l'argile varient sans doute avec les dimensions et la nature des particules de charbon. Les particules de la taille d'un grain de sable comprennent des particules dont les propriétés superficielles et le pouvoir d'adsorption varient. En général, on retrouve les particules plus fraîch-es et plus légères de charbon, aux propriétés hydrophobes, dans les fractions argileuses, tandis que le limon renferme des particules plus lourdes, enrobées d'argiles ou aux pores remplis d'argile. Les ultrasons utilisés pour désagréger les sols peuvent fractionner les grosses particules en d'autres, plus petites. Le sol et les fractions qui résistent à l'oxydation ...
