Models are an important means to improve our understanding through the testing of different hypotheses and scenarios. We will integrate our knowledge of the physics, chemistry and biology of soils derived both in this WP3.1 and others (particularly WP 4) into computer simulation models. In order to facilitate objective evaluation of models and hypotheses we intend to develop methodology to discriminate between alternative models using Bayesian techniques. Specifically we intend to develop a new dynamic model of the strength of soils and integrate this with models of the formation and fate of dissolved organic carbon and nitrogen in soil coupled to our existing models of nutrient cycling. WP3.1 seeks to improve our understanding of the interaction between mechanical impedance to root growth and changes in the moisture characteristics and we will explore the interactions of these physical processes with DOC and nutrient cycling in soils and their combined effects on plants. This research has direct parallels to that in the Scottish MRP WPs 3.3, 3.4 and 3.2, in particular with the Macaulay Institute through a 'root-level' understanding of processes, especially water movement, and root growth and development and SCRI objective 1.72: "Physical constraints to plant and microbial processes" as part of workpackage 1.7 "Sustainable crop systems" Alignment of SoilCIP and Scottish MRP research will facilitate the development of fully interacting models of biogeochemical cycles that explain complex process and systems level behaviour.