Geoscience Reference
In-Depth Information
recent Sahara desert or in the large Indian desert Thar running along the border
between India and Pakistan. Isotope studies of layers of the Thar Desert show wet
periods during the last two interglacials. Having mentioned the decrease of the areal
extent of deserts according to paleosol studies, we also note increased areas of des-
ert. Deep drilling in all recent deserts and semideserts shows that the extent of des-
erts was largest about 25,000-20,000 years ago during the coolest period of the last
Wisconsin (or Würm) glacial. During this time period, based primarily on carbon
isotope studies, this cool “peak” occurred in the last glacial with the extreme global
dryness.
Importance of the study of paleosols was discovered in agriculture and ecology,
since the knowledge of local remnants of paleosol enables us to predict the next
change of soil properties due to eventual introduction of new plant types and culti-
vation techniques, or under the infl uence of industrial and generally technological
activity. We have to keep in mind that ongoing increasing or decreasing changes of
contemporary soil fertility cannot be accurately predicted based on only a few years
of measurements or even those observed for a sequence of several decades. To truly
understand the reality of seasonal local weather coupled with global climate
demands that we deal with scales that connect decades with hundreds and thousands
of years. Such changes would be irreversible under natural conditions, and if the
change was in the direction of decreased soil fertility, the amelioration would be
very expensive, even if possible at all. Briefl y saying, the knowledge of the soil his-
tory enables us to understand the recent and future changes.
13.4
Maps of the Soil Distribution
There are two types of soil maps. In a simpler or local case, the map covers a rela-
tively small area with a scale in ranges roughly 1:100 to 1:1,000. It is frequently
ordered by the farmer or by the consortium of several farmers, or by the authority of
a local or regional district. Sometimes when farmers or owners of land need more
specifi c information than is normally displayed on an ordinary small-scale soil map,
they request a soil cartogram that illustrates the geographical presentation of a cer-
tain soil property - like soil pH, soil texture, depth of A horizon, quantities of avail-
able plant nutrients, etc. The elaboration of such a map requires that a soil scientist
has an effective combination of brain and brawn, brawn because strong, agile legs
are needed to walk through the landscape while looking for appropriate locations
into which soil pits are next dug with a shovel using the strength of powerful biceps.
His brain decides the initial number and spacing of the pits. If his brawn is defi cient
or if he gets too tired to dig all of the pits, he depends on younger colleagues to fi n-
ish the digging. After all of the pits are completely dug out, the soil scientist walks
back and forth between each and every pit several times in order to personally make
detailed observations and measurements within each profi le and to remove large
numbers of soil samples that must be analyzed in the laboratory. His brain takes the
next step to identify the geographical distribution of specifi c soil properties based
