Evaluation of Assouline–Or Adjusted Model to Express Soil Drainage Curve

The objectives of this research are prediction of soil drainage curve using Assouline and Or (2014) adjusted soil drainage model and comparison of the predicted results with experimental data on small and large scales. This research is conducted for 18 small soil columns under different salinity level of irrigation water using different scenarios. In scenario A, water from saturated water and water of 0.1 (A-1) and 15 (A-2) bar matric head assumed as the mobile water, D∞, and input to Assouline and Or model to estimate weighted average of hydraulic conductivity, Km with fitting. In scenario B, Km is computed using water characteristic curve and D∞ is obtained using fitted model. Finally, in scenario C, D∞ and Km are predicted using fitted model. All experiments were repeated in the presence of plant for small soil columns and columns with 2.7 m depth as well. Results showed that the model prediction is influenced by irrigation water salinity, study time and depth scales. However, soil and water physical properties and their interactions can partially explain the results and the flexibility of Assouline and Or model is appropriate, we suspected to the validity of physical meaning of model parameters and, the certainty of model predictions for the field capacity, FC, concept.