Arid and Desert Soils
Arid Soil range from red to brown in color. They are generally sandy in texture and saline in nature. In some areas the salt content is very high and common salt is obtained by evaporating the water. Due to the dry climate, high temp., evaporation is faster and the soil lacks humus and moisture. The lower horizons of the soil are occupied by kankar because of the increasing calcium content downwards. The kankar layer formation in the bottom horizons restrict the infiltration of water. After proper irrigation these soils become cultivable as has been in the case of western Rajasthan( INDIA ).
The varied geological terrains of the Sonoran Desert provide many different kinds of parent materials in which soils form. Gravelly or stony alluvial fans that spill out of mountain drainages into adjacent basins cover much of the face of the Sonoran Desert ( see the chapter “The Geologic Origin of the Sonoran Desert” ). The sediments transported all the way to the floors of these basins are usually much finer — sands, silts and clays. The mountains themselves possess various rock types, slopes, and exposures that offer a complex array of different soil – forming environments. The monstrous heaps of wind – blown sand in the dune fields of the Gran Desierto in northwestern Sonora and the Cactus Plain east of Parker, Arizona, provide yet another kind of soil parent material. Large, flat areas devoid of vegetation and covered by a layer of tightly packed small stones are conspicuous features of extremely arid landscapes. These desert pavements are rare or absent in the moister parts of the Sonoran Desert, but become increasingly pronounced in the driest parts.
Closeup of tightly packed stones in a desert pavement. The dark stones are varnish – covered pieces of volcanic rhyolite; the white pieces are quartz on which varnish usually does not form. Some of the most extensive and well – developed areas of desert pavements occur on stony alluvial fan deposits flanking the rugged, low mountains in the extremely arid lower Colorado River Valley. Geologically young deposits ( Holocene – aged, less than 11,000 years ) lack the flat – surfaced pavements. Surfaces of these young deposits are typically cluttered with large stones and rocks irregularly piled in elevated bars; these low bars are separated by intervening swales. This stony jumble of bars and swales is the topographic imprint of the surface’s creation by the powerful tumult of moving water laden with rocky debris. Over time, though, this imprint disappears as the vertical relief of these coarse, rocky deposits is leveled out, eventually forming the flat pavement of small stones. The best – developed pavements are those that have formed over the passage of several tens of thousands to a few hundreds of thousands of years.