Proisotropic and Proanisotropic Processes
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.