Systems approach to water productivity assessment using cropping system Models

Irrigation management of crops in Egypt is characterized by the application of more water than the crops require. In fact, large amounts of water are supplied without any estimates of the soil water content at the root zone. The rationale for doing so is the assumption that more irrigation water means a greater yield. So, eliminating the use of this unnecessary irrigation water could help save the resource, provided that this can be done with low yield losses.
The estimation of soil water reserves in the root zone area is essential for the best irrigation management. This management can be done by modeling water depletion from the root zone under the application of different amounts of irrigation water (Khalil et al., 2007). Models that simulate crop growth and water flow in the root zone can be powerful tools for extrapolating findings and conclusions from field studies to conditions not tested (Smith et al., 2000). Therefore, using these types of models to predict the effect of applying deficit irrigation on the yield of several crops could be an ultimate solution to conserving irrigation water.
Deficit irrigation, while it may result in a yield reduction, in general increases water productivity and has the added benefit that the irrigation water saved can be used in new lands. However, testing these deficit irrigation practices in the field is expensive. Therefore, simulation models could partially substitute for experiments to test different deficit irrigation scenarios and be used to develop recommendations for the conservation of irrigation water and the minimizing of yield losses. Three models were selected for that purpose, CROPWAT, Yield-Stress and CropSyst. Our objective was to use these models to assess the effects of different deficit irrigation scenarios on the yields of crops planted in the field trials.