Visualization of the three-dimensional water-flow paths in calcareous soil using iodide water tracer

In this paper we modified a spray method to visualize iodide water tracer in calcareous soil with high pH, and developed a process to combine multiple soil horizontal sections to establish three-dimensional (3-D) visualization modeling for water-flow paths in soil. In the modified spray method, pH adjuster was misted onto the soil surface to lower soil pH after starch solution with oxidizer (ferric ion) had been sprayed onto the soil profile irrigated by iodide-labeled water. The acidic condition accelerated the distinct purple-blue color of iodine-starch. When images of multiple soil horizontal sections stained by iodine-starch complex were captured by digital camera, the iodine-starch color stained pattern on the soil surface was outlined using software ImageJ (developed at the US National Institutes of Health). After all 3-D coordinates were outlined with dots, 3-D visualization modeling for water-flow paths in soil was established using software Surfer 8.0 (Golden Software Inc.) as an alternative method for studying water infiltration and distribution behavior in soil.