Evaluation of WatSuit Model for Prediction of Alfalfa's Root Zone Salt Distribution Pattern

When irrigating with saline water, salt distribution pattern within the root zone is affected by leaching fraction and crop water uptake pattern, in addition to the chemical interactions of soil solution. In order to evaluate leaching requirement and sensitivity of alfalfa to salinity, a lysimetric study (cylindrical lysimeters with internal diameters of 40cm and height of 180 cm) was conducted in completely randomized design with 3 levels of irrigation water salinity (3, 7 and 13 dS/m) and 3 levels of leaching fractions (12%, 25%, and 50 %) as a factorial experiment with 4 replications. After packing, soil columns were leached until drainage water salinity reached 3 dS/m and, then, were sown with alfalfa (Yazdi cultivar). To prepare different irrigation water salinity, natural saline water from Sadouq Salinity Research Field with salinity level of 14 dS/m was blended with tap water in different ratios. The amount of applied water was based on crop water consumption in addition to leaching fraction which was carefully weighed. The collected drain water was weighed again after 48 hr in which drain water quality was measured too. The least required irrigation cycles to reach steady state conditions was 12 cycles which increased with increasing salinity level and decreasing leaching fraction. Generally, results showed that implementation of a defined leaching fraction can reduce soil salinity more than WatSuit predictions. Therefore, soil salinity control at a desired level can be obtained with less leaching fraction level. This is especially important for optimum water utilization under saline conditions when irrigation is linked to application of more salts.