Evaluation of the DSSAT Vertical Drainage Model for Vertisols

The increasing competition for water has led to the need for a better water resources management, especially for crops irrigation. A water balance tool in crop models is useful for the determination of the best agricultural water management practices that maximize the crop yield and the water productivity while avoiding the need for costly field experiments. This requires that crop models simulate water balance accurately. Suleiman and Richie (2004) (SR2004) developed a vertical drainage equation which has been incorporated into the Decision Support System for Agrotechnology Transfer (DSSAT) which is the most widely used crop model in the world. The objective of this study is to test the performance of SR2004 in Vertisols of Jordan. A laboratory trial was conducted on three Vertisols columns. The soil water content was measured daily at different soil depths during drainage cycles to test the vertical drainage model. The root mean square difference between the simulated and measured volumetric soil water contents across the three replicates ranged between 0.0039 and 0.0471 cm3/cm3. Excellent estimation was obtained for soil water content during the drainage cycles for columns (1 and 2) at all depths with the nRMSE ranging from 2.6212 to 6.4606 cm^3/cm^3. While for column (3), the soil water content was at an excellent estimated level except at the depths of 12 cm and 16 cm where it was estimated as good. The simulation results obtained revealed that the SR2004 overestimated the soil water content during the drainage cycle, thus, the SR2004 model needs modification to perform better regarding Vertisols.