Removal of nitrogen and phosphate by the circulation of percolated water and paddy rice growth

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Purification capability of nitrogen for paddy soil has been studied in the paddy field. In the present study, paddy rice was cultivated in pot soil under the percolation of water with and without circulation, and the concentration of nitrogen in the soil solution has been measured for three months. The same experiments were conducted for the pot soil without paddy rice. The concentration of NH_4-N in the pot soil without paddy rice showed about 2.5mg/L irrespective of time under both circulated and uncirculated water percolation. This could be attributed to the continuous dissolution of ammonium adsorbed on the clay surface. The concentration of NH_4-N in the pot soil with paddy rice became zero after twenty days since the percolation started. This tendency was the same irrespective of the percolation rate. The reduction rate of ammonium in the pot soil was 93 to 99% for the soil with paddy rice, and 73 to 94% for the soil without paddy rice. The crop of rice showed a little difference between the pot soil with and without water circulation, and due to the difference of percolation rate. Thus, the paddy soil exhibited high ammonium removal capability and this capability entirely depended on the adsorption by soils and the absorption by paddy rice.