Descriptions of crop water uptake/transpiration are of widely varying complexity and employ considerably different approaches. This paper examines simple approaches that could be used in crop growth simulation models for application in land use systems analysis. Many apparently conceptual differences stem from different interpretations of averaged or generalised data, and the dogmatic use of pragmatic ad hoc choices. Proliferation of terms has perhaps contributed more to mystification than to clarification of the problems involved. Simplified theoretical descriptions based on physical laws have their merits, e.g. for educational purposes or for practical assessments if they are properly tested throughout their range of application. However, they can only be applied in practice using "default parameters" and/or "surrogate" input data. In this way, models that are intended to explain may degenerate and there is no reason why they would be more appropriate than empirical approaches. For empirical approaches, it is concluded that using, e.g. "soil water depletion fraction" or "soil water potential" to indicate the limit of readily available soil water is an arbitrary choice. Most water uptake models were originally designed and tested for irrigated crops with a closed canopy. Adaptations to different conditions rely heavily on intuitive interpretations. Models suited to rain fed conditions must be able to handle situations where wet and dry parts of the soil occur side by side and an "average soil water status" seems meaningless. Field experiments to test alternative approaches are scarce. Therefore, many uncertainties persist, that call for further research. Land use systems studies should attempt to quantify these uncertainties by numerical analyses as a routine activity.
- land use
- crop yield
- soil water
- plant water relations
van den Berg, M., & Driessen, P. M. (2002). Water uptake in crop growth models for land use systems analysis. I. A review of approaches and their pedigrees. Agriculture, Ecosystems and Environment, 92, 21-36. https://doi.org/10.1016/S0167-8809(01)00285-7