On the Decrease of NO3-N Concentration of Flow Water in Paddy Field Plots

Abstract

We continue the long term experiment on nitrate removal in the paddy field plots. Natural water with high nitrate concentration of approximately 20 mg L-1 was supplied to each plot continuously more than ten years. Nitrate removal rates gradually decreased in the first few years, but now they keep the ability of nitrate removal. In this paper, the decrease of nitrate concentration and water temperature in the flow process was measured at 3 hours intervals. Water temperature was lowest in the first block and it gradually increased through flow process (Fig. 2). The values of nitrate concentration decreased linearly and did not change so much by time as shown in Fig. 4. Average nitrate removal rate (R) of non-plant plot was 0.61 g m-2 d-1. The coefficients of nitrate removal rate (a) were calculated by the equation (9) and the average coefficient of nitrate removal rate (a) was 0.038 m d_1. The coefficient of nitrate removal rate of the first block was smaller than the values of other blocks due to low water temperature (Fig. 9).