Abstract.Land evaluation involves the definition of the comparative marginal value of individual land areas for the uses being considered. For agricultural land evaluation crop yields are the most reliable estimates of comparative marginal values. Yield values can be obtained from field measurements, as well as from productivity indices and empirical and mechanistic crop growth models. This paper reviews the pros and cons of each approach. Mechanistic models of the summary type, that simulate only those processes that are critical to describe an agroecosystem, are the most realistic and practical tools for land evaluation. Criteria for these types of models are given.