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

在水田中研究了氮素对水稻土的净化能力。本研究采用盆栽土壤，在有和无循环水的渗滤条件下栽培水稻，连续3个月测定土壤溶液中氮的浓度。对不种植水稻的盆栽土进行了同样的试验。在循环水和非循环水渗流条件下，不种植水稻的盆土中NH_4-N浓度与时间无关，均在2.5mg/L左右。这可能是由于吸附在粘土表面的铵不断溶解所致。水稻盆栽土中NH_4-N的浓度在渗流开始20天后变为零。无论渗透速率如何，这种趋势都是相同的。盆栽土中铵态氮的还原率，水稻土为93 ~ 99%，不水稻土为73 ~ 94%。有水循环和无水循环的盆土，由于渗流速率的差异，水稻的产量差异不大。由此可见，水稻土具有较高的铵离子脱除能力，其脱除能力完全取决于土壤的吸附和水稻的吸附。

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.