Geoderma, 55 (1992) 183-210 183 Elsevier Science Publishers B.V., Amsterdam Towards the quantitative modeling of pedogenesis - a review Marcel R. Hoosbeek and Ray B. Bryant Department of Soil, Crop and Atmospheric Sciences, Cornell University, Ithaca, NY, USA (Received March 3, 1992; accepted after revision June 6, 1992 ) ABSTRACT Hoosbeek, M.R. and Bryant, R.B., 1992. Towards the quantitative modeling of pedogenesis - a review. Geoderma, 55: 183-210. The historical development of our pedogenetic model is reviewed, and trends or directions toward the future are discussed. Pedogenetic models are characterized with respect to relative degree of com- putation, complexity, and level of organization. These three characteristics are used as a framework for classification. Early qualitative models have well served the purpose of soil survey to describe the distribution of soils in landscapes. Further development of qualitative models will contribute to the understanding of soil genesis in areas where soil surveys are not completed. In the developed coun- tries, however, the scientific questions have changed dramatically. Greater interest lies in understand- ing the physical and chemical processes of soil formation acting within relatively short time frames and assessing the interactions between natural processes and environmental change or anthropogenic impacts. Quantification of pedogenetic processes is a life-line to other environmental disciplines, and a mechanistic understanding would, in an ideal situation, describe and predict the behavior of a sys- tem for a limited number of years under changing environmental conditions. A proposed approach to mathematical simulation of the dynamic pedogenetic processes is to inte- grate soil physical, chemical, and other ecological system models into a quantitative pedogenetic model. Models may be developed as research tools in data-intensive studies at the pedon or horizon level, or for the purpose of simulating a soil system at the catena or soil region level. Specific kinds of pedoge- netic models have specific implications with respect to the availability and spatial variability of the data needed for development and testing. INTRODUCTION Scientific knowledge is based on the interaction between observations and the hypotheses that correspond with those observations (Popper, 1959; France and Thornley, 1984). The continual interaction between hypotheses (how we think or expect things to work) and observations (attempts to measure the real world) leads to progress in our scientific knowledge. This scientific Correspondence to: M.R. Hoosbeek, Cornell University, 701 Bradfield Hall, Ithaca, NY 14853, USA. 0016-7061 / 92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.