Abstract
We intend to use rice straw as a organic substance for denitrification to remove nitrogen from soil percolate, and examined its feasibility by column experiments. We prepared the soil columns of 52 mm inner diameter with rice straw put in as a mono-layer, and supplied 20 mg-N per litter potassium nitrate solution to them from the upper surface at the rate of 24, 47 or 94 mm per day. Nitrate hardly was observed in the effluent from the column supplied at 94 mm per day for 114 days, and nitrate nitrogen removal during the period was 490 mg-N, which was roughly 5% of the amount of rice straw. Other columns fed at lower rate exhibited much lower nitrogen removal, the decrease in nitrogen concentration did not observed after 40 days of operation in these columns.
From the fact that the column fed at the largest flow rate showed the largest amount of denitrification, and from the examination of mass balance of nitrogen in soil and rice straw, we concluded that the removal of nitrogen by the column fed at 94 mm per day was mainly due to denitrification.
We conclude that we can use rice straw as a organic material source for denitrification to remove nitrate from soil percolate. The anoxic condition at the place where rice straw should be put in is essential to the effective use of rice straw.
