Twenty-five years modeling irrigated and drained soils: State of the art.

Half of the world food production originates from irrigated and drained soils. Advanced soil water flow simulation models have the potential to contribute to the solution of relatively complex problems in irrigation and drainage science and management, provided that field data are available to calibrate and run them. Besides providing a literature review, this paper emphasizes on calibration and mathematical optimization procedures using GIS and remote sensing techniques. Unfortunately, the required level of expertise of integrated GIS, remote sensing and models make the application of sophisticated tools highly dependent on modeling experts. This is one of the chief reasons that soil water flow models have a low operational focus, especially in less developed countries with irrigation systems where they are most needed. The gap between the supply of various advanced models and the application by the irrigation and drainage community needs to be closed. The likelihood of adoption by a broader model user community will increase if models become more user and data-friendly (or -tolerant) and heterogeneity-aware. During the next 10 years, simulation model development and application should focus on agricultural water savings, understanding recycling of water in the basin context, increase crop water productivity, bring groundwater-overexploitation to a halt and control the build up of soil salinity.