Geoscience Reference
In-Depth Information
C. Marbut introduced the idea of soil evolution stemming from Dokuchaev's con-
cept. Marbut gradually extended the Russian system to US environmental and soil
conditions between 1921 and 1935. It is worth mentioning that among his contem-
porary soil scientists bearing PhD degrees, he never bothered to take the fi nal exam
for his PhD at Harvard where he obtained his Master of Arts. In addition to observ-
ing and understanding interconnecting links between various components of natu-
rally occurring soil processes, he was also fl uent in German and was among the soil
scientists preparing the foundation of the International Soil Science Society (ISSS)
at the Prague conference in 1922. ISSS was fi nally established in 1924 at the Fourth
International Conference of Pedology. His contacts with the European soil scientists
enabled him to learn of Glinka's topic that he translated into English in 1927. With
this readily available translation, it was easy for US soil scientists to extend these
new approaches. Indeed until 1935, Marbut himself published several drafts of soil
classifi cation according to his knowledge about the new concepts. At that time the
system's highest taxonomic level designated soils into three soil groups - zonal,
intrazonal, and azonal. It was a unique, meritorious achievement of Marbut that US
soil scientists started to play an important role in soil classifi cation by applying and
extending theoretical taxonomic principles that eventually led to the present-day US
Taxonomic System.
The main objective of this system is to defi ne all factors infl uencing the evolution
of the taxon and its relation to a neighboring taxon. This is achieved by a strict hier-
archical arrangement with fl exibility in grouping taxons. The system recognizes six
descending levels that start at the top level of
orders
and below them sequential
levels of
suborders
,
great groups
,
subgroups
,
family
, and
series
. Each soil has its
name composed of syllables characterizing all levels. For example, soils belonging
to
order
Alfi sol will have the last syllable, or more precisely the formation element
alf
. If it has the udic moisture regime, then its
suborder
name is
Udalf
. The name is
derived from the Latin
udus
which means moist. If the soil is well drained, has a
horizon rich in clay that does not have an abrupt upper boundary, has a relatively
high base saturation, is relatively deep, and has only a weak horizon development,
the soil belongs to the
great group
named
Hapludalf
. The name is derived from the
Greek
haplous
meaning simple. When the soil has cracks in its top horizon and no
other dominant properties of Vertisols, the soil fi ts into
subgroup Vertic Hapludalfs
.
The above example shows that the US Taxonomy created a large number of new
words. A brief, scientifi cally incomplete explanation of the highest taxonomic level
terms,
orders
, will follow together with one example of one
suborder
, one
great
group
, and fi nally one
subgroup
of many others. The aim here is just to show how
new names are formed in each of the orders. The topic
Keys to Soil Taxonomy
elabo-
rated by Soil Survey Staff contains full information needed for appropriate designa-
tion of a fi eld soil. There are also the rules for the identifi cation of families like
particle size classes, soil depth, soil slope classes, etc. Below, we do not review or
explain the two lowest taxonomic levels -
family
and
series
.
But it may be worth noting that the series, the fi eld mapping units, have remained
unchanged in spite of all the shenanigans of innumerable changes in classifi cation
since the establishment of the soil survey under Milton Whitney. This is the genius
