Influence of percolation pattern on the removal of soluble ions in stratified paddy field with rice and the gravel under the plowsole

摘要

We used a model of a stratified paddy field (plow layer, plowsole and subsoil) with the gravel under the plowsole that exist in volcanic ash areas beside flood plains. These models were planted with rice and were fertilized. The models were used to investigate the removal of soluble ions in percolation water under different percolation patterns; the open system percolation and the closed system percolation. The results are as follows. In the case of high drainage levels, plow layer, plowsole and subsoil became the closed system percolation and were made into reduction layers. But in the case of low drainage levels, only subsoil became the open system percolation and were made into a oxidation layer. Concentrations of nitrate ion, nitrous ion, iron ion, manganese ion and dissolved oxygen in water of the closed system percolation increased more than those in the open system percolation. Potassium ion concentrations in plow layer and plowsole increased during the 50 days from the start of examination as compared with its concentration in the subsoil. Concentration of the total nitrogen in drainage was higher than those in inundation during 60 days as well as total phosphorus during 30 days. After these periods, the two concentrations were nearly equal.