Agriculture Reference
In-Depth Information
practical requirement in natural bodies with wide textural ranges, as in some cases found by
Turner (2000). Another question is how confusing it is going to be to the users of soil information
if series are not mutually exclusive and overlap partially in regard to something such as texture.
Reactivation of a soil classiÝcation working group was started toward the end of 1996 by
the Soil Science Society of South Africa (SSSSA). This was stimulated by the WRB workshop
in South Africa in September 1996. A small steering committee met in February 1997 to set
things in motion. The two most important recommendations by the steering committee from an
international perspective are these:
¤
That the other countries from the Southern African Development Community (SADC) should also
be included, and that the activities of the working group should not be limited to South Africa.
Unfortunately this has not yet materialized.
¤
That greater liaison and coordination with the World Reference Base for Soil Resources (WRB)
Working Group must be encouraged.
It was emphasized that the working group must strive to satisfy the needs of our clients (land
users, students, consultants, etc.) and not alienate them. The working group met just after the
SSSSA congress in July 1999 to get some points on the agenda, and held a fruitful workshop
just before the SSSSA congress in January 2001. Progress is slow because there is no funding
for the working group, and no institution has been given the responsibility to drive its activities.
The 2001 workshop was encouraging because a number of deÝnite proposals were discussed in
depth. These included the creation of new forms for soils with new diagnostic horizon sequences
that have been found. At last someone has been assigned the task of coming up with a deÝnite
proposal for a concept deÝnition for what we want soil series to be, as previously discussed.
From an international perspective, the two most relevant points handled at the workshop are:
¤ The deÝnition and classiÝcation of soils with vertic properties. The WRBÔs decision to deÝne the
vertic horizon as a subsurface horizon caused quite a stir, and the question was whether South
Africa should go the same way, instead of having a Vertic A horizon. In South Africa, there are
many Prismacutanic B and Pedocutanic B horizons with vertic properties, i.e., strong swell-shrink
properties and perfect slickensides. The vast majority of soils with these horizons have relatively
sandy topsoils with no swell-shrink properties and no structure. It was decided to keep the Vertic
A horizon, because the classical Vertisol is not only a soil with a clayey topsoil, but which is
distinguished from other structured clayey topsoils (Melanic A horizons) on the basis of its strong
swell-shrink properties. The swell-shrink properties of the topsoil cause it to have speciÝc land-
use problems and to have special management requirements. From an engineering point in partic-
ular, it is important to map out soils with vertic subsoils. Thus it was decided to also recognize
vertic properties in subsoils, and to probably make provision for these at family level in the soils
with Prismacutanic B and Pedocutanic B and G horizons.
¤How
diagnostic horizons/properties should be handled in the classiÝcation system.
No provision is made for these in the 1991 classiÝcation system. The need for attention to them
was expressed by WRB Working Group members during the 1996 workshop in South Africa. Soils
with gypsiferous horizons are found in the extreme aridic western part of the country (Ellis, 1988).
Salic soils are found in various parts of the semiarid and arid regions. Ellis was given the task of
drawing up proposals for their handling in the classiÝcation system. My proposal was that the
handling of these in the WRB system should be used as a starting point, and adapted for South
African conditions.
gypsic
and
salic
THE ROAD AHEAD
It seems that the approach and structure for the deÝnition of diagnostic horizons and the
classiÝcation of soil forms seem well accepted and do not have to be changed. New diagnostic
horizons (e.g., gypsic and salic) and new forms can be added as new information becomes
