Agriculture Reference
In-Depth Information
many of the Kandiudults have properties more akin to Oxisols than to Ultisols (Beinroth et al.,
1974; Eswaran and Tavernier, 1980).
Another concern is that management-induced soil erosion may selectively remove part of the
Ýne fraction from the surface horizon. The resulting textural differentiation may cause a change in
the classiÝcation from Oxisols to Ultisols or AlÝsols that is anthropogenic rather than pedogenic
in nature (Eswaran et al., 1986). From a management point of view, the low nutrient holding capacity
and absence of a potential to supply some of the nutrients (characteristics of Oxisols) are more
restricting than the small clay increase required by a kandic horizon (Herbillon, 1980). Van
Wambeke (1989) also objected to the use of the kandic horizon in two opposite directions at the
same level in the hierarchical structure, as the rationale is difÝcult to understand: The horizon is
used, on the one hand, to include soils in the Oxisols, and on the other hand, to exclude soils from
the Oxisols.
Although we believe that there were no compelling reasons for introducing the kandic horizon,
it is now a
. Nevertheless, if there was a consensus that the kandic horizon properties
should be diagnostic for Oxisols, they could have been considered more elegantly. It could have
been accomplished by deleting item 5 (clay increase with depth) from the deÝnition of the oxic
horizon, and changing item E in the Key to Soil Orders (Soil Survey Staff, 1999) to read: ÑOther
soils that have an oxic horizon that has its upper boundary within 150 cm of the mineral soil
surface.Ò The Oxisols that have an argillic horizon (as currently deÝned) would become Argi or
Kandi great groups. The AlÝsols and Ulltisols would then have a CEC greater than 16 cmol per
kg clay, and those with CEC between 16 and 24 cmol per kg clay would become Kandi great
groups. Such a change would maintain class purity and the logic of the system. Sys (1968) already
proposed this option.
fait accompli
CONCLUSION
Soil Taxonomy is a dynamic system that must be updated periodically to accommodate new
knowledge and thus to ensure that it can accomplish its stated purpose of Ñmaking and interpreting
soil surveys.Ò However, necessary revisions should only be considered after a thorough review of
adequately documented proposals has conÝrmed their validity. Moreover, as Soil Taxonomy aspires
to be an international system, such reviews should involve the global pedologic community. This
protocol is not always followed, as the recent change in the deÝnition of the iso soil temperature
regimes exempliÝes. Yet to abide by the proper procedures is often easier said than done. This is
particularly true for users of Soil Taxonomy in less-developed tropical countries. They may have
solid qualitative and intuitive evidence for needed changes, but lack the human and capital resources
to document their concern with factual Ýeld and laboratory data.
Regrettably, the USDA Natural Resources Conservation Service, the custodian of Soil Taxon-
omy, cannot provide assistance as it is constrained by its Congressional mandate that requires it to
use allocated funds only for domestic programs. In the past, the Soil Management Support Services,
a project funded by the U.S. Agency for International Development (USAID), provided such
technical assistance and also a forum for discussion of issues of concern. The project was set up
to advance the adoption of Soil Taxonomy in the interest of global communication and agrotech-
nology transfer. In spite of its success, it was terminated by USAID. We consider this unfortunate,
as the new users of Soil Taxonomy are now left without technical support. This may result in
unilateral and haphazard changes to the system. As a consequence, Soil Taxonomy may gradually
lose global relevance and degenerate into a parochial scheme of national applicability. We regret
this development and believe that it would be in the interest of USAID to again contribute to a
process, which will foster the global use and application of the system.
The second edition of Soil Taxonomy, which was published in 1999, is the result of enormous
efforts to improve the system. Nonetheless, the process appears to have been
ad hoc
to some extent,
