干旱区生态环境知识资源中心

The objectives of this work were: (i) to document the micromorphological, physical, and chemical properties of soil crusts types; and (ii) to determine the factors that control crust formation. Soil crusts as Av-horizons were studied in three different soil classifications: Typic Calciorthid, Typic Haplargid, and Typic Natrargid. The Av-horizons showed common characteristics such as high silt and low organic matter. contents. The high exchangeable sodium percentage (ESP) is considered the main cause of crust formation in the Av-horizons of the Haplargid and Natrargid. The crusts lying below the desert pavement consist of an upper zone of laminated sands, silts and clays, large vesicles, and a very dense lower zone with few and small vesicles. The size of the vesicles differ greatly among the three studied crusts. The vesicular layers of the Natrargid are more developed than of other soils. The typical shape of vesicles is rough walled on the upper half and smooth at the bottom. The walls of larger vesicles, close to the surface area, are subjected to microerosion and microdeposition by the action of a descending water front. The Av-horizon of the Natrargid seems to be formed by the Bt itself, with a differential development of pores and structure. The papules in the Av-horizons of the Haplargid and Natrargid correspond to residual argillans, strongly fragmented and deformed by stress. Both micromorphological and scanning electron microscope (SEM) observations show evidence of a lateral rather than a vertical transport of material. The main processes responsible for crust formation are considered to be a combination of erosion by raindrop impact and re-deposition by rainwash.