Crop irrigation scheduling is conventionally based on any one of (1) soil water balance (SWB)calculations, (2) crop growth simulation models, (3) soil water measurements, (4) sensing ofthe plant's response to water defi cits or, on farmers’ experience.In the fi rst approach, the irrigation schedule is calculated based on reference evaporation anda crop-specifi c empirical crop coeffi cient. There are inaccuracies with this approach, due toassuming that plant growth is solely dependent on calendar time, ignoring the infl uence ofthermal time and water supply on crop development.Crop growth models consist of algorithms that try to mimic the main physiological plantprocesses through a set of assumptions and calibration parameters. One major advantage ofsuch models compared to empirical approaches is their spatial and temporal transferability.They are widely used to support decision making, as well as for yield gap or scenario analyses.Irrigation scheduling based on soil water tension measurements have several advantages:e.g. the soil water tension is closely related to plant stress, these measurements can beprecise and easy to apply, and irrigation can be automated. Diffi culties arise from evaluatingwhere exactly to probe; particularly when high spatial heterogeneity exists in soil.
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