Prediction and Control of Salt Accumulation in the Upper Root Zone Under Sub-Surface Drip Irrigation.

We have conducted a greenhouse experiment using two soil tanks in each of which 16 TDR probes were inserted horizontally. Masa loamy sand and Kanto loam were filled into each tank and soybean was sown. After the leaf area became about 300cm2, subsurface drip irrigation from a porous pipe inserted at a depth of 12 cm with 5000 ppm CaCl2 solution was started. When the soil became saline enough to retard transpiration, leaching through the subsurface porous pipe was performed. The wetting front reached to the soil surface and a part of salts presented above the porous pipe was transported to soil surface.
We have also incorporated root water uptake submodel into our numerical model (WASH_2D) for two-dimensional water and solute movement. We have added thermal vapor diffusion by plainly inter/extrapolating measured soil temperature. The numerical solutions by WASH_2D were in fair agreement with the measured water content and salt concentration as well as those distribution at the end.