Geoscience Reference
In-Depth Information
15
Desert soils, paleosols and duricrusts
Excellent soil scientists for some kinds of research, including detailed
soil surveys, fail utterly in reconnaissance soil mapping. They may be
unable to visualize large and complex patterns and become mentally
harassed by indecision in the face of vague and apparently
conflicting evidence.
U.S. Department of Agriculture
Soil Survey Manual , Agricultural Handbook 18
(1951, pp. 437-438)
15.1 Introduction
The three most important natural resources in all drylands (and, indeed, in less arid
areas) are water, soils and vegetation. Soils in the arid world differ from their humid
counterparts in being generally low in organic matter. In addition, they are often saline
and/or alkaline (Williams, 1968b ; Amit and Yaalon, 1996 ). Both of these factors limit
plant growth and constrain human use of desert soils. The broad distribution of such
soils is reasonablywell-known both globally (FAO, 1991 ; IUSSWorkingGroupWRB,
2007 ), on a continental scale (e.g., McKenzie et al., 2004 ;SoilSurveyStaff, 2010 )
and on a national scale (e.g., Chinese Soil Taxonomic Classification, 1991 ), although,
of course, all soils mapping is provisional, as new methods of remote sensing and
geochemical mapping improve apace.
Within the drylands, not all soils are currently active and in balance with the present-
day bioclimatic environment. Scattered across many deserts, there are sporadic
remains of former soils, as well as more resistant formations cemented with car-
bonate, iron, silica or gypsum that are termed duricrusts . The relict soils are variously
referred to as fossil soils, or paleosols , implying that they are no longer forming
(Yaalon, 1971 ; Birkeland, 1999 ; Retallack, 2001 ). The presence of such soils in hyper-
arid areas indicates that the climate was once wetter than it is today (Khadkikar et al.,
2000 ), because soils need both moisture and biological activity in order to develop.
258
Search WWH ::




Custom Search