Assessing crop water productivity from field to regional scale

As previous co-workers of Dr. Jans Wesseling, who headed the Department of Water Management of the Institute for Land and Water Management Research, i.e. the ‘Instituut voor Cultuurtechniek en Waterhuishouding’ (ICW), Wageningen from 1959 to 1987, we have written the present review article. We start with a short description of the hydrological problems, with a particular focus on groundwater, that affect agriculture in humid and temperate climates such as that of the Netherlands as well as in semi-arid climates. We then describe the highlights of the scientific career of Dr. Wesseling, who inspired us and colleagues that have worked with soil water flow under both saturated and unsaturated conditions in relation to the creation of optimal conditions for plant growth and yield. This is followed by an overview of the transient flow modeling of water and solute flow in heterogeneous soil–root systems under a variety of boundary conditions with a focus on the linkage between water use by the crop, and daily crop growth and crop yield, i.e. the so-called ‘water productivity’ relationship. Then the agreement between long-term predictions made with dynamic land capability models and field measurements are discussed in the context of model utility to establish design criteria for drainage systems for both humid as well as for semi-arid areas.