II. DESERT SOILS
61
area of chloride and sulfate accumulations. The foothills and low mountains would constitute the general areas of carbonate and silicate concentration. Although this may be a general concept for broad desert flats,
narrow desert valleys may appear as exceptions and may or may not
collect salts depending on local conditions. Much of the Chilean Atacama
Desert, for example, is entirely barren of plants (Cameron et al., 1965).
Salts have accumulated in many places as borax "lakes," saline "dry lakes,"
and nitrate deposits which have provided exports.
Parent materials markedly influence the salt relationships in the arid
soils of Western United States. In general, the parent materials contain
moderate to high levels of alkaline-earth carbonates and soluble salts. Salts
accumulate in these soils in or below the horizons of maximum carbonate
accumulation. Carbonates, however, are found well distributed throughout
the soil profile. The Gobi Desert is an example of a desert devoid of gypsum but fairly high in lime. At the other end of the central Asian Desert,
Turkestan Desert soils accumulate gypsum. The difference is claimed to
be due to differences in sulfate composition of parent materials. The broad
processes affecting salt in desert soils are weathering and the transportation
and accumulation of weathered products.
VII. Desert Soils as a Medium for Plants
A. MOISTURE
Moisture is the single most limiting factor for plant growth in desert
soils. Water the soil and "the desert shall blossom as the rose" has been
predicted many times in history (Thorne, 1951). Because water in arid
climates is so limiting, an unusual amount of attention has been focused
on soil-water-plant relationships.
Desert soils differ from most other soils with respect to their ability to
take up or infiltrate rainwater. Many desert soils are dry and hard. Some
are crusted. These characteristics markedly reduce the water infiltration
rate. The beating action of raindrops on barren or near barren soils compacts the surface, reducing porosity. Raindrop action also keeps the surface
layer dispersed. No matter how thin the dispersed layer is, it acts as a
barrier to water infiltration. Certain salts, especially those containing sodium, cause soils to disperse, resulting in a low rate of water penetration
and movement in the profile. As a consequence of many such factors,
much of the rain that falls on sloping desert land runs off into low places
and collects in basins where evaporation further concentrates salts in an
already salty soil.
Clearing of the land of vegetation accelerates water runoff, reduces the
61
area of chloride and sulfate accumulations. The foothills and low mountains would constitute the general areas of carbonate and silicate concentration. Although this may be a general concept for broad desert flats,
narrow desert valleys may appear as exceptions and may or may not
collect salts depending on local conditions. Much of the Chilean Atacama
Desert, for example, is entirely barren of plants (Cameron et al., 1965).
Salts have accumulated in many places as borax "lakes," saline "dry lakes,"
and nitrate deposits which have provided exports.
Parent materials markedly influence the salt relationships in the arid
soils of Western United States. In general, the parent materials contain
moderate to high levels of alkaline-earth carbonates and soluble salts. Salts
accumulate in these soils in or below the horizons of maximum carbonate
accumulation. Carbonates, however, are found well distributed throughout
the soil profile. The Gobi Desert is an example of a desert devoid of gypsum but fairly high in lime. At the other end of the central Asian Desert,
Turkestan Desert soils accumulate gypsum. The difference is claimed to
be due to differences in sulfate composition of parent materials. The broad
processes affecting salt in desert soils are weathering and the transportation
and accumulation of weathered products.
VII. Desert Soils as a Medium for Plants
A. MOISTURE
Moisture is the single most limiting factor for plant growth in desert
soils. Water the soil and "the desert shall blossom as the rose" has been
predicted many times in history (Thorne, 1951). Because water in arid
climates is so limiting, an unusual amount of attention has been focused
on soil-water-plant relationships.
Desert soils differ from most other soils with respect to their ability to
take up or infiltrate rainwater. Many desert soils are dry and hard. Some
are crusted. These characteristics markedly reduce the water infiltration
rate. The beating action of raindrops on barren or near barren soils compacts the surface, reducing porosity. Raindrop action also keeps the surface
layer dispersed. No matter how thin the dispersed layer is, it acts as a
barrier to water infiltration. Certain salts, especially those containing sodium, cause soils to disperse, resulting in a low rate of water penetration
and movement in the profile. As a consequence of many such factors,
much of the rain that falls on sloping desert land runs off into low places
and collects in basins where evaporation further concentrates salts in an
already salty soil.
Clearing of the land of vegetation accelerates water runoff, reduces the