SOLUTE TRANSPORT THROUGH HARD PANS OF PADDY FIELDS .1. EFFECT OF VERTICAL TUBULAR PORES MADE BY RICE ROOTS ON SOLUTE TRANSPORT

We simulated non-sorbed Br- transport through hard pans of paddy fields by using a coaxial cylindrical model. In the model, only one parameter was used. The model was adapted to 4 kinds of hard pans. All calculated values were close to the measured values. The results proved that vertical tubular pores made by rice roots whose radii were less than 1 mm had as significant an effect on solute transport as transmission pores in the hard pans. When the mean velocity in the pores was faster, solute discharged rapidly through them before diffusing well into the soil matrix. On the other hand, when the mean velocity in the pores was slower, solute discharged slowly while sufficiently diffusing into the soil matrix.