The STEP-AWBH model provides a conceptual framework for modeling of soil properties and classes. It is one of the most comprehensive soil-factorial models that accounts for spatial and temporal variations of soil-environmental factors. The model is described in detail in these slides.
This article describes the STEP-AWBH model:
Grunwald S., J.A. Thompson and J.L. Boettinger. 2011. Digital soil mapping and modeling at continental scales – finding solutions for global issues. Soil Sci. Soc. Am. J. (SSSA 75th Anniversary Special Paper) 75(4): 1201-1213. (pdf)
This article provides an application of the STEP-AWBH model:
Xiong X., S. Grunwald, D.B. Myers, J. Kim, W.G. Harris and N.B. Comerford.. 2014. Holistic environmental soil-landscape modeling of soil organic carbon. Environmental Modeling and Software J. 57: 202-215. (pdf)