ReviewDeficit irrigation as an on-farm strategy to maximize crop water productivity in dry areas
Section snippets
Rationale
To sustain the rapidly growing world population, agricultural production will need to increase (Howell, 2001), yet the portion of fresh water currently available for agriculture (72%) is decreasing (Cai and Rosegrant, 2003). Hence, sustainable methods to increase crop water productivity are gaining importance in arid and semi-arid regions (Debaeke and Aboudrare, 2004). Traditionally, agricultural research has focused primarily on maximizing total production. In recent years, focus has shifted
The concept
Crop water productivity (WP) or water use efficiency (WUE), as reviewed by Molden (2003), is a key term in the evaluation of DI strategies. Water productivity with dimensions of kg m−3 is defined as the ratio of the mass of marketable yield (Ya) to the volume of water consumed by the crop (ETa):ETa refers to water lost either by soil evaporation or by crop transpiration during the crop cycle. Since there is no easy way of distinguishing between these two processes in field experiments,
The concept of deficit irrigation
Deficit irrigation is an optimization strategy in which irrigation is applied during drought-sensitive growth stages of a crop. Outside these periods, irrigation is limited or even unnecessary if rainfall provides a minimum supply of water. Water restriction is limited to drought-tolerant phenological stages, often the vegetative stages and the late ripening period. Total irrigation application is therefore not proportional to irrigation requirements throughout the crop cycle. While this
Modeling as a tool for assessing and developing deficit irrigation strategies
Examining the yield response to different water applications in field and/or controlled experiments is laborious and expensive. Nor can such experiments cover all possible combinations of differential drought stress or all environmental aspects affecting yield. Moreover, differential response to drought stress during different phenological stages can cause considerable scatter in the CWPc function. Against this background, modeling can be a useful tool to study and develop promising DI
Conclusion
Considerable field information is available on the use of deficit irrigation for common and less common crops. In line with the reference works of Hanks et al. (1969), Hanks (1974), Stewart et al. (1977), Doorenbos and Kassam (1979) and Taylor et al. (1983), the relation between crop evapotranspiration and yield is proposed as a framework for evaluating the drought sensitivity of a particular crop during the season or during a specific growth stage. These crop water production functions are
Acknowledgements
Research funded by a PhD grant of the Flemish Interuniversity Council (VLIR) and by the K.U.Leuven Research Fund for post-doctoral fellowships. We extend our gratitude to Maarten Fauvart and the anonymous reviewers for substantial comments on earlier versions of this article and to Kristin Blanpain for considerable language improvements.
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