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- S = f(cl, o, r, p, t, …)
- S is for soil
- cl (sometimes c) represents climate
- o organic activity
- r relief
- p parent material
- t time
There are two principal methods that the state equation may be solved: first in a theoretical or conceptual manner by logical deductions from certain premises, and second empirically by experimentation or field observation. The empirical method is still mostly employed today, and soil formation can be defined by varying a single factor and keeping the other factors constant. This led to the development of empirical models to describe pedogenesis, such as climofunctions, biofunctions, topofunctions, lithofunctions, and chronofunctions. Since Hans Jenny published his formulation in 1941, it has been used by innumerable soil surveyors all over the world as a qualitative list for understanding the factors that may be important for producing the soil pattern within a region.
The term clorpt is mainly used for empirical quantitative prediction with the purposes of making digital soil maps. In this approach, the state-factor equation was put explicitly into a spatial framework and the factors were also observed in the same spatial domain. Some people have termed the approach environmental correlation, associated with using stratigraphy, digital terrain models and gamma radiometric surveys, to predict and map soil properties.
- Amundson, Jenny (January 1991). "THE PLACE OF HUMANS IN THE STATE FACTOR THEORY OF ECOSYSTEMS AND THEIR SOILS.". Soil Science: An interdisciplinary approach to soil research. Retrieved 30 November 2015.
- Johnson; et al. (March 2005). "Reflections on the Nature of Soil and Its Biomantle.". Annals of the Association of American Geographers. Retrieved 30 November 2015.