2002 年 25 巻 9 号 p. 565-570
An investigation on water quality was conducted in a small catchment of a tea field for three years, and runoff loads of total nitrogen (T-N), total phosphorus (T-P) and chemical oxygen demand (COD) were estimated. Runoff quantity was estimated using a water-balance equation. The annual runoff loads of T-N were estimated to be 61.0 kg·ha-1 for the first year, 193 kg·ha-1 for the second year, and 88.1 kg·ha-1 for the third year, and the average load for the three years was 114.1 kg·ha-1. The ratio of the nitrogen load to the amount of applied nitrogen fertilizer was 17.1%, being much lower than in previous studies. The main reason for the low ratio obtained in this study was the lower concentration of nitrogen. The annual runoff loads of T-P and COD were estimated to be 0.68 kg·ha-1 and 59 kg·ha-1, respectively, and both were affected by the flushing effect on rainy days. This result suggests the importance of monitoring of phosphorus and COD as well as nitrogen in upland fields.