Proisotropic and Proanisotropic Processes
of
Pedoturbation
Randall J. Schaetzl
Because pedoturbation processes
(soil mixing) occur in all soils in varying degrees during the course of their evolution,
mixing processes should be assessed within the larger context of soil
genesis. Soils may be viewed as
evolving along two pedogenic pathways that operate concurrently: a progressive
pathway that includes processes, factors, and conditions that promote ordered,
differentiated and/or deep profiles; and a regressive pathway that promotes
disordered, simplified, rejuvenated, and/or shallow profiles. Pedoturbative processes that disrupt, blend,
destroy, or prevent the formation of horizons, subhorizons, or genetic layers,
such that simplified profiles evolve from more ordered ones, are proisotropic and function within the
regressive pathway. Pedoturbative
processes that form or aid in the formation and maintenance of horizons,
subhorizons, or genetic layers and/or promote increased profile order are proanisotropic and function within the
progressive pathway.
Ten forms of pedoturbation are
recognized. Hypothetical and real
examples of how proisotropic and proanisotropic mixing processes affect soil
profiles are presented. The examples
demonstrate that both the form of
pedoturbation and the texture of the
parent material largely determine whether the ensuing morphology of a soil
expresses order or disorder. A
particular form of pedoturbation may produce a disordered profile in one soil
or polypedon, but a more ordered profile in another. This can be true not only for different soils on a landscape, but
also for the same soil at different times during its evolution. Homogeneous or heterogeneous geologic
deposits may be pedologically organized, or reorganized, via proanisotropic
pedoturbation to express profile order and in certain cases may produce spatial
patterning and microrelief. Surface
stone pavements and armored surfaces, subsurface stone lines and stone zones,
and upper profile biomantles can thus be formed.